@misc{bremser_dauelsberg_strauch_2005, title={Method for depositing in particular crystalline layers, and device for carrying out the method}, volume={6,972,050}, number={2005 Dec. 6}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Bremser, M. and Dauelsberg, M. and Strauch, G. K.}, year={2005} } @misc{davis_nam_zheleva_bremser_2003, title={Gallium nitride semiconductor structures including lateral gallium nitride layers}, volume={6,570,192}, number={2003 May 27}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Davis, R. F. and Nam, O.-H. and Zheleva, T. and Bremser, M. D.}, year={2003} } @misc{davis_nam_zheleva_bremser_2003, title={Methods of fabricating gallium nitride semiconductor layers by lateral overgrowth}, volume={6,602,763}, number={2003 Aug. 5}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Davis, R. F. and Nam, O.-H. and Zheleva, T. and Bremser, M. D.}, year={2003} } @article{pozina_edwards_bergman_monemar_bremser_davis_2001, title={Time-resolved photoluminescence in strained GaN layers}, volume={183}, number={1}, journal={Physica Status Solidi. A, Applications and Materials Science}, author={Pozina, G. and Edwards, N. V. and Bergman, J. P. and Monemar, B. and Bremser, M. D. and Davis, R. F.}, year={2001}, pages={151–155} } @article{pozina_edwards_bergman_paskova_monemar_bremser_davis_2001, title={Time-resolved spectroscopy of strained GaN/AlN/6H-SiC heterostructures grown by metalorganic chemical vapor deposition}, volume={78}, ISSN={["0003-6951"]}, DOI={10.1063/1.1350421}, abstractNote={Temperature-dependent time-resolved photoluminescence measurements were performed on GaN film/AlN buffer/6H–SiC substrate heterostructures grown by metalorganic chemical vapor deposition. The overlying GaN layers were under tension, as estimated from the free A exciton (FEA) position. The recombination lifetimes were determined for the FEA and for the neutral-donor-bound exciton (D0X). We observed that the recombination lifetime for the FEA has the same value of 40–50 ps in all the layers, whereas the recombination time for the D0X varies for different samples. We observed that the recombination lifetimes for D0X have a clear dependence on the position of FEA, i.e., the recombination lifetime increases with decreasing strain in the layers. We discuss the results in term of the hole states involved in the donor-bound exciton recombination.}, number={8}, journal={APPLIED PHYSICS LETTERS}, author={Pozina, G and Edwards, NV and Bergman, JP and Paskova, T and Monemar, B and Bremser, MD and Davis, RF}, year={2001}, month={Feb}, pages={1062–1064} } @misc{davis_nam_zheleva_bremser_2000, title={Gallium nitride semiconductor structures including a lateral gallium nitride layer that extends from an underlying gallium nitride layer}, volume={6,051,849}, number={2000 Apr. 18}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Davis, R. F. and Nam, O.-H. and Zheleva, T. and Bremser, M. D.}, year={2000} } @article{edwards_bremser_batchelor_buyanova_madsen_yoo_welhkamp_wilmers_cobet_esser_et al._2000, title={Optical characterization of wide bandgap semiconductors}, volume={364}, ISSN={["0040-6090"]}, DOI={10.1016/S0040-6090(99)00903-7}, abstractNote={Our work primarily concerns the characterization of wide-gap III-V nitride semiconductors, nondestructively and at variable temperature, with spectroscopic ellipsometry (SE) and reflectometry in the spectral range from 1.5 to 6 eV. In the case of GaN, there are three main concerns associated with such data: (a) the quantification of the dispersion of the index of refraction with energy, (b) the removal of surface overlayers in real-time, and (c) the determination of the variation of valence bands with biaxial stress and the quantification of residual stress in thin films. The SE and reflectance capabilities provide (1) broadband spectra from 1.5 to 6 eV, which yield information about (a) below the bandgap and (b) above it, and (2) high resolution spectra (less than 1 meV at 3.4 eV) in the vicinity of the gap (3.3-3.6 eV), which enables (c). Here we will discuss issues concerning the relation of (c) to GaN material and growth parameters, though similar data for other wide bandgap materials will be discussed where relevant. Specifically, optimal heterostructure design for potential valence band engineering applications will be discussed in the context of trends in residual stress as a function of film thickness, growth temperature and substrate orientation for GaN/AlN/6H-SiC heterostructures. Standard heterostructures are mostly compressive for samples less than about 0.7 µm thick, are tensile up to about 2 µm and then abruptly become less tensile with stress values near 1 kbar thereafter. Additionally, these trends can be circumvented for moderately thick (approximately 2 µm) GaN layers (normally>2 kbar, tensile) by the introduction of a `buried interface' approach, namely, a strain mediating layer (SML) above the standard high-temperature AlN buffer layer designed to yield a range of compressive stresses from 0 to 2 kbar. The strain characteristics but also the growth rates of subsequently deposited nitride layers can be modulated by changing the growth parameters of the SML. This is achieved by in situ techniques during crystal growth without degrading the optical and structural properties of the deposited layer, as confirmed by XRD, SEM, PL, and AFM data taken on the overlying GaN layers. These results are interpreted in terms of coefficient of thermal expansion data for the layers and data concerning the planarization of GaN layers and growth behavior in non-(0001) directions.}, number={1-2}, journal={THIN SOLID FILMS}, author={Edwards, NV and Bremser, MD and Batchelor, AD and Buyanova, IA and Madsen, LD and Yoo, SD and Welhkamp, T and Wilmers, K and Cobet, C and Esser, N and et al.}, year={2000}, month={Mar}, pages={98–106} } @article{buyanova_wagner_chen_edwards_monemar_lindstrom_bremser_davis_amano_akasaki_1999, title={Electronic structure of the 0.88-eV luminescence center in electron-irradiated gallium nitride}, volume={60}, number={3}, journal={Physical Review. B, Condensed Matter and Materials Physics}, author={Buyanova, I. A. and Wagner, M. and Chen, W. M. and Edwards, N. V. and Monemar, B. and Lindstrom, J. L. and Bremser, M. D. and Davis, R. F. and Amano, H. and Akasaki, I.}, year={1999}, pages={1746–1751} } @article{skierbiszewski_suski_leszczynski_shin_skowronski_bremser_davis_1999, title={Evidence for localized Si-donor state and its DX-like properties in AlGaN: Errata (vol 74, pg 3833, 1999)}, volume={75}, number={20}, journal={Applied Physics Letters}, author={Skierbiszewski, C. and Suski, T. and Leszczynski, M. and Shin, M. and Skowronski, M. and Bremser, M. D. and Davis, R. F.}, year={1999}, pages={3225A} } @article{skierbiszewski_suski_leszczynski_shin_skowronski_bremser_davis_1999, title={Evidence for localized Si-donor state and its metastable properties in AlGaN}, volume={74}, ISSN={["0003-6951"]}, DOI={10.1063/1.124195}, abstractNote={Transport studies of AlxGa1−xN (0.5 4 kbar, tensile) of moderately thick (∼2 μm) GaN based structures grown on 6H-SiC to a range 0 to -2 kbar of compressive stresses by introducing a strain-mediating layer (SML) above the standard high-temperature AlN buffer layer. The strain characteristics of subsequently deposited nitride layers can be modulated by changing the growth parameters of the SML layer. This is achieved by in-situ techiniques during crystal growth without degrading the optical and structural properties of the deposited layers.}, number={G3.78}, journal={MRS Internet Journal of Nitride Semiconductor Research}, author={Edwards, N. V. and Batchelor, A. D. and Buyanova, I. A. and Madsen, L. D. and Bremser, M. D. and Davis, R. F. and Aspnes, D. E. and Monemar, B.}, year={1999} } @article{bidnyk_little_schmidt_cho_krasinski_song_goldenberg_yang_perry_bremser_et al._1999, title={Stimulated emission in GaN thin films in the temperature range of 300-700 K}, volume={85}, ISSN={["1089-7550"]}, DOI={10.1063/1.369325}, abstractNote={We report the results of an experimental study on stimulated and spontaneous emission from high-quality single-crystal GaN films grown on 6H-SiC and (0001) sapphire substrates in the temperature range of 300–700 K. We observed edge-emitted stimulated emission (SE) at temperatures as high as 700 K for samples grown on both SiC and sapphire substrates. The energy position of the SE and spontaneous emission peaks were shown to shift linearly to longer wavelengths with temperature and empirical expressions for the energy positions are given. We demonstrate that the energy separation between the spontaneous and SE peaks gradually increases from 90 meV at 300 K to 200 meV at 700 K indicating that an electron-hole plasma is responsible for the SE mechanism in this temperature range. The temperature sensitivity of the SE threshold for different samples was studied and the characteristic temperature was found to be 173 K in the temperature range of 300–700 K for one of the samples studied. We suggest that the unique properties of SE in GaN thin films at high temperatures could potentially be utilized in optoelectronic devices.}, number={3}, journal={JOURNAL OF APPLIED PHYSICS}, author={Bidnyk, S and Little, BD and Schmidt, TJ and Cho, YH and Krasinski, J and Song, JJ and Goldenberg, B and Yang, W and Perry, WG and Bremser, MD and et al.}, year={1999}, month={Feb}, pages={1792–1795} } @article{bremser_perry_nam_griffis_loesing_ricks_davis_1998, title={Acceptor and donor doping of AlxGa1-xN thin film alloys grown on 6H-SiC(0001) substrates via metalorganic vapor phase epitaxy}, volume={27}, ISSN={["0361-5235"]}, DOI={10.1007/s11664-998-0392-9}, number={4}, journal={JOURNAL OF ELECTRONIC MATERIALS}, author={Bremser, MD and Perry, WG and Nam, OH and Griffis, DP and Loesing, R and Ricks, DA and Davis, RF}, year={1998}, month={Apr}, pages={229–232} } @article{perry_bremser_davis_1998, title={Cathodoluminescence studies of the deep level emission bands of AlxGa1-xN films deposited on 6H-SiC(0001)}, volume={83}, ISSN={["0021-8979"]}, DOI={10.1063/1.366716}, abstractNote={A comprehensive study of the sub band-edge emission bands of AlxGa1−xN (0.06⩽x⩽1) thin films deposited on vicinal and on-axis 6H–SiC(0001) substrates is presented. At 4.2 K strong band-edge emission, ascribed to donor-bound excitons, shallow donor-shallow-acceptor pair emission, and a deep emission band associated with the “yellow” band of GaN, were observed via cathodoluminescence. The energy shift of the shallow donor-shallow-acceptor pair band with respect to the peak of the donor-bound excitons peak exhibited a less than one-to-one correspondence with increasing Al mole fraction due the increasing localization of either the shallow donor and/or shallow acceptor. The yellow band was observed for all compositions and exhibited a similar energy shift with respect to both the donor-bound excitons and the shallow donor-shallow-acceptor pair bands as the Al mole fraction increased, except for a brief decrease at x≈0.5. This decrease was attributed to a donor oxygen level which entered the band gap at approximately this composition. A strong, broad emission band observed at 3.25 eV at 295 K in AlN and commonly associated with oxygen impurities was shown to be closely related to the yellow band of GaN.}, number={1}, journal={JOURNAL OF APPLIED PHYSICS}, author={Perry, WG and Bremser, MB and Davis, RF}, year={1998}, month={Jan}, pages={469–475} } @article{king_barnak_bremser_tracy_ronning_davis_nemanich_1998, title={Cleaning of AlN and GaN surfaces}, volume={84}, ISSN={["0021-8979"]}, DOI={10.1063/1.368814}, abstractNote={Successful ex situ and in situ cleaning procedures for AlN and GaN surfaces have been investigated and achieved. Exposure to HF and HCl solutions produced the lowest coverages of oxygen on AlN and GaN surfaces, respectively. However, significant amounts of residual F and Cl were detected. These halogens tie up dangling bonds at the nitride surfaces hindering reoxidation. The desorption of F required temperatures >850 °C. Remote H plasma exposure was effective for removing halogens and hydrocarbons from the surfaces of both nitrides at 450 °C, but was not efficient for oxide removal. Annealing GaN in NH3 at 700–800 °C produced atomically clean as well as stoichiometric GaN surfaces.}, number={9}, journal={JOURNAL OF APPLIED PHYSICS}, author={King, SW and Barnak, JP and Bremser, MD and Tracy, KM and Ronning, C and Davis, RF and Nemanich, RJ}, year={1998}, month={Nov}, pages={5248–5260} } @article{kaminska_piotrowska_jasinski_kozubowski_barcz_golaszewska_bremser_davis_1998, title={Interfacial microstructure of Ni/Si-based ohmic contacts to GaN}, volume={94}, ISSN={["0587-4246"]}, DOI={10.12693/APhysPolA.94.383}, abstractNote={Development of low-resistance, thermally stable ohmic contacts is one of the big challenges for the progress in the GaN device technology. We have recently reported on novel Ni/Si-based metallization systems providing ohmic contacts on GaN [1]. We have adopted the idea of Sands et al. [2] of the incorporation of a dopant into the semiconductor subcontact region by solid-phase dissolution and regrowth (SPR). To produce contacts to p-type GaN, Mg dopant is added to the Ni/Si metallization; for n-type GaN, Si is the intended donor dopant [1]. We have shown that these contacts exhibit ohmic behavior after annealing at temperatures ranging from 400 to 600°C, with resistivities of about 1 x 10 -3 Ω cm2 at p-type (p 3 x 10 17 cm-3) and n-type (n 2 x 10 17 cm-3) GaN. The preliminary characterization using Rutherford backscattering spectrometry (RBS), secondary ion mass spectrometry (SIMS), and X-ray diffraction (XRD) indicated that several thermally activated solid-phase processes take place during the formation of ohmic contacts. However, a full understanding of these processes and their influence on the metal/GaN interface properties is still lacking. This study will focus on microstructure of Ni/Si-based contacts. In order to investigate structural properties such aS interface abruptness, phase composition, and defects in the contact region we have applied crosS-sectional tran8mission}, number={3}, journal={ACTA PHYSICA POLONICA A}, author={Kaminska, E and Piotrowska, A and Jasinski, J and Kozubowski, J and Barcz, A and Golaszewska, K and Bremser, MD and Davis, RF}, year={1998}, month={Sep}, pages={383–386} } @article{shan_fischer_hwang_little_hauenstein_xie_song_kim_goldenberg_horning_et al._1998, title={Intrinsic exciton transitions in GaN}, volume={83}, ISSN={["0021-8979"]}, DOI={10.1063/1.366660}, abstractNote={Intrinsic excitonic transitions in GaN have been studied using a variety of spectroscopic measurements. Sharp spectral structures associated with intrinsic free excitons could be observed in photoluminescence, reflection, and absorption spectra. The energy positions of excitonic transitions in GaN epitaxial layers were found to be influenced by the residual strain resulting from lattice-parameter and thermal-expansion mismatches between the epilayers and the substrates. The values of the four principal deformation potentials of wurtzite GaN were derived by using the strain tensor components determined by x-ray measurements. The observation of spectral features involving the emission of LO phonons in absorption and photoluminescence excitation spectra at energies above exciton resonances indicate that a phonon-assisted indirect excitation process, which simultaneously generates a free exciton and a LO phonon, is a very significant and efficient process in GaN. The lifetime of the free excitons is found to be longer than the relaxation time of LO-phonon emission but much shorter than that of acoustic-phonon emission.}, number={1}, journal={JOURNAL OF APPLIED PHYSICS}, author={Shan, W and Fischer, AJ and Hwang, SJ and Little, BD and Hauenstein, RJ and Xie, XC and Song, JJ and Kim, SS and Goldenberg, B and Horning, R and et al.}, year={1998}, month={Jan}, pages={455–461} } @article{wisniewski_knap_malzac_camassel_bremser_davis_suski_1998, title={Investigation of optically active E-1 transversal optic phonon modes in AlxGa1-xN layers deposited on 6H-SiC substrates using infrared reflectance}, volume={73}, ISSN={["1077-3118"]}, DOI={10.1063/1.122273}, abstractNote={We report an investigation, performed in the full composition range x=0–1, of the change in infrared reflectivity spectra of AlxGa1−xN layers deposited on 6H–SiC substrates. We have found two different transverse E1(TO) phonon frequencies that can be assigned to AlN-like and GaN-like modes. The composition dependences of these frequencies can be well approximated by linear functions and the oscillator strengths scale like the corresponding Al and Ga mole fractions, respectively. On a purely experimental basis, this establishes evidence of a two-mode behavior for this controversial alloy system. The frequencies of the impurity mode of Ga in AlN (622 cm−1) and of the impurity mode of Al in GaN (643 cm−1) were determined.}, number={13}, journal={APPLIED PHYSICS LETTERS}, author={Wisniewski, P and Knap, W and Malzac, JP and Camassel, J and Bremser, MD and Davis, RF and Suski, T}, year={1998}, month={Sep}, pages={1760–1762} } @article{nam_zheleva_bremser_davis_1998, title={Lateral epitaxial overgrowth of GaN films on SiO2 areas via metalorganic vapor phase epitaxy}, volume={27}, ISSN={["0361-5235"]}, DOI={10.1007/s11664-998-0393-8}, number={4}, journal={JOURNAL OF ELECTRONIC MATERIALS}, author={Nam, OH and Zheleva, TS and Bremser, MD and Davis, RF}, year={1998}, month={Apr}, pages={233–237} } @article{dalmer_restle_sebastian_vetter_hofsass_bremser_ronning_davis_wahl_bharuth-ram_1998, title={Lattice site location studies of ion implanted Li-8 in GaN}, volume={84}, ISSN={["1089-7550"]}, DOI={10.1063/1.368463}, abstractNote={The lattice sites of ion implanted Li atoms in GaN were studied as a function of implantation temperature between room temperature and 770 K. We measured the channeling and blocking patterns of α-particles emitted in the radioactive decay of implanted Li8 ions to determine the Li lattice sites. Below 700 K Li atoms occupy mainly interstitial sites in the center of the c-axis hexagons at positions c/4 and 3c/4, where c is the lattice constant in c-axis direction. Around 700 K Li starts to diffuse and presumably interacts with vacancies created in the implantation process. This leads to the formation of substitutional Li above 700 K. An activation energy of about 1.7 eV for interstitial Li diffusion was determined.}, number={6}, journal={JOURNAL OF APPLIED PHYSICS}, author={Dalmer, M and Restle, M and Sebastian, M and Vetter, U and Hofsass, H and Bremser, MD and Ronning, C and Davis, RF and Wahl, U and Bharuth-Ram, K}, year={1998}, month={Sep}, pages={3085–3089} } @misc{stutz_mack_bremser_nam_davis_look_1998, title={Photoelectrochemical capacitance-voltage measurements in GaN}, volume={27}, ISSN={["0361-5235"]}, DOI={10.1007/s11664-998-0182-4}, number={5}, journal={JOURNAL OF ELECTRONIC MATERIALS}, author={Stutz, CE and Mack, M and Bremser, MD and Nam, OH and Davis, RF and Look, DC}, year={1998}, month={May}, pages={L26–L28} } @article{edwards_yoo_bremser_horton_perkins_weeks_liu_stall_kuech_davis_et al._1998, title={Spectroscopic ellipsometry and low-temperature reflectance: complementary analysis of GaN thin films}, volume={313}, ISSN={["0040-6090"]}, DOI={10.1016/S0040-6090(97)00815-8}, abstractNote={Abstract We report spectroscopic ellipsometry (SE) and low-temperature reflectance data on epitaxial GaN thin-film samples covering the widest range of tensile and compressive stress (−3.8 to 3.5 kbar) thus far. SE allows us to assess the preparation of smooth and abrupt GaN surfaces by chemical treatments in real time, and, coupled with the reflectance data, the E d n /d E contribution to dispersion, which is important for laser action. The reflectance data explicitly show the non-linear behavior of the B-A and C-A splittings vs. the energy of the A exciton. Lineshape ambiguities that hindered previous interpretations have been resolved with reciprocal space analysis, allowing us to obtain band parameters such as Δ SO =17.0±1 meV and Δ CF =9.8±1 meV with increased confidence.}, number={1998 Feb.}, journal={THIN SOLID FILMS}, author={Edwards, NV and Yoo, SD and Bremser, MD and Horton, MN and Perkins, NR and Weeks, TW and Liu, H and Stall, RA and Kuech, TF and Davis, RF and et al.}, year={1998}, month={Feb}, pages={187–192} } @article{edwards_bremser_davis_batchelor_yoo_karan_aspnes_1998, title={Trends in residual stress for GaN/AlN/6H-SiC heterostructures}, volume={73}, ISSN={["1077-3118"]}, DOI={10.1063/1.122597}, abstractNote={We discuss trends in residual stress as a function of film thickness, growth temperature, and substrate orientation for GaN/AlN/6H–SiC heterostructures. Films are mostly compressive for samples less than about 0.7 μm thick, are tensile up to about 2 μm, then abruptly become less tensile with stress values near 1 kbar thereafter. We interpret this as a successive relief of lattice mismatch and thermal stresses culminating in a catastrophic relief by unknown mechanisms at moderate thicknesses. These data indicate that relaxation processes in these heterostructures are not as well understood as previously supposed.}, number={19}, journal={APPLIED PHYSICS LETTERS}, author={Edwards, NV and Bremser, MD and Davis, RF and Batchelor, AD and Yoo, SD and Karan, CF and Aspnes, DE}, year={1998}, month={Nov}, pages={2808–2810} } @article{zheleva_nam_bremser_davis_1997, title={Dislocation density reduction via lateral epitaxy in selectively grown GaN structures}, volume={71}, ISSN={["0003-6951"]}, DOI={10.1063/1.120091}, abstractNote={The microstructure and the lateral epitaxy mechanism of formation of homoepitaxially and selectively grown GaN structures within windows in SiO2 masks have been investigated by transmission electron microscopy (TEM) and scanning electron microscopy. The structures were produced by organometallic vapor phase epitaxy for field emission studies. A GaN layer underlying the SiO2 mask provided the crystallographic template for the initial vertical growth of the GaN hexagonal pyramids or striped pattern. The SiO2 film provided an amorphous stage on which lateral growth of the GaN occurred and possibly very limited compliancy in terms of atomic arrangement during the lateral growth and in the accommodation of the mismatch in the coefficients of thermal expansion during cooling. Observations with TEM show a substantial reduction in the dislocation density in the areas of lateral growth of the GaN deposited on the SiO2 mask. In many of these areas no dislocations were observed.}, number={17}, journal={APPLIED PHYSICS LETTERS}, author={Zheleva, TS and Nam, OH and Bremser, MD and Davis, RF}, year={1997}, month={Oct}, pages={2472–2474} } @article{davis_weeks_bremser_tanaka_kern_sitar_ailey_perry_wang_1997, title={Growth of AlN and GaN thin films via OMVPE and gas source MBE and their characterization}, volume={41}, ISSN={["1879-2405"]}, DOI={10.1016/S0038-1101(96)00152-9}, abstractNote={Thin films of AlN and GaN are deposited primarily via the common forms of organometallic vapor phase epitaxy (OMVPE) and molecular beam epitaxy (MBE). Sapphire is the most common substrate; however, a host of materials have been used with varying degrees of success. Both growth techniques have been employed by the authors to grow AlN and GaN primarily on 6H-SiC(0001). The mismatch in atomic layer stacking sequences along the growth direction produces inversion domain boundaries in the AlN at the SiC steps; this sequence problem may discourage the nucleation of GaN. Films of AlN and GaN grown by MBE at 650°C are textured; monocrystalline films are achieved at 1050°C by this technique and OMVPE. Donor and acceptor doping of GaN has been achieved via MBE without post growth annealing. Acceptor doping in CVD material requires annealing to displace the H from the Mg and eventually remove it from the material. High brightness light emitting diodes are commercially available; however, numerous concerns regarding metal and nitrogen sources, heteroepitaxial nucleation, the role of buffer layers, surface migration rates as a function of temperature, substantial defect densities and their effect on film and device properties, ohmic and rectifying contacts, wet and dry etching and suitable gate and field insulators must and are being addressed.}, number={2}, journal={SOLID-STATE ELECTRONICS}, author={Davis, RF and Weeks, TW and Bremser, MD and Tanaka, S and Kern, RS and Sitar, Z and Ailey, KS and Perry, WG and Wang, C}, year={1997}, month={Feb}, pages={129–134} } @article{davis_bremser_perry_ailey_1997, title={Growth of AlN, GaN and AlxGa1-xN thin films on vicinal and on-axis 6H-SiC(0001) substrates}, volume={17}, ISSN={["0955-2219"]}, DOI={10.1016/S0955-2219(97)00077-0}, abstractNote={Monocrystalline GaN(0001) thin films were grown at 950 °Con AlN(0001) buffer layers previously deposited at 1100 °C on α(6H)-SiC(0001)si substrates via metallorganic chemical vapor deposition (MOCVD). Films of AlxGa1 − xN (0 ≤ x ≤ 1) were grown directly on the same SiC surface at 1100 °C. X-ray rocking curves for the GaN(0004) reflection for 1.4 μm films revealed FWHM values of 58 and 151 arc sec for materials grown on on-axis and offaxis substrates, respectively. Cathodoluminescence exhibited strong near band-edge emission for all materials. Controlled n- type Si-doping in GaN and AlxGa1 − xN (for x ≤ 0.4) was achieved with net carrier concentrations ranging from approximately 2 × 1017 cm− 3 to 2 × 1019 (AlxGa1 − xN) or to 1 × 1020 (GaN) cm− 3. Mg-doped, p-type GaN and AlxGa1 − xN (for x ≤ 0.13) was achieved with nA − nD ≈ 3 × 1017 cm− 3.}, number={15-16}, journal={JOURNAL OF THE EUROPEAN CERAMIC SOCIETY}, author={Davis, RF and Bremser, MD and Perry, WG and Ailey, KS}, year={1997}, pages={1775–1779} } @article{nam_bremser_ward_nemanich_davis_1997, title={Growth of GaN and Al0.2Ga0.8N on patterened substrates via organometallic vapor phase epitaxy}, volume={36}, ISSN={["0021-4922"]}, DOI={10.1143/JJAP.36.L532}, abstractNote={ The selective growth of GaN and Al0.2Ga0.8N has been achieved on stripe and circular patterned GaN/AlN/6H-SiC(0001) multilayer substrates. Growth morphologies on the stripe patterns were a function of the widths of the stripes and the flow rate of triethylgallium. No ridge growth was observed along the top edges of the truncated stripe patterns. Smooth (0001) top facets formed on stripes ≥5 µ m wide. Uniform hexagonal pyramid arrays of undoped GaN and Si-doped GaN were successfully grown on 5 µ m circular patterns. Field emission measurements of a Si-doped GaN hexagonal pyramid array exhibited a turn-on field of 25 V/µ m for an emission current of 10.8 nA at an anode-to-sample distance of 27 µ m. }, number={5A}, journal={JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS}, author={Nam, OH and Bremser, MD and Ward, BL and Nemanich, RJ and Davis, RF}, year={1997}, month={May}, pages={L532–L535} } @article{bremser_perry_zheleva_edwards_nam_parikh_aspnes_davis_1997, title={Growth, doping and characterization of AlxGa1-xN thin film alloys on 6H-SiC(0001) substrates}, volume={6}, ISSN={["0925-9635"]}, DOI={10.1016/S0925-9635(96)00626-7}, abstractNote={Thin films of AlxGa1 − xN (0.05≤x≤0.96) having smooth surfaces were deposited directly on both vicinal and on-axis 6H-SiC(0001) substrates. Cross-sectional transmission electron microscopy of Al0.13Ga0.87N revealed stacking faults near the SiC/nitride alloy interface and numerous threading dislocations. Energy dispersive analysis, Auger electron spectroscopy (AES) and Rutherford backscattering were used to determine the compositions. These were paired with their respective cathodoluminescence (CL) near band-edge emission energies. A negative bowing parameter was determined. The CL emission energies were similar to the bandgap energies obtained by spectroscopic ellipsometry. Field emission AES of the initial growth of Al0.2Ga0.8N revealed an Al-rich layer near the interface. N-type (Si) doping was achieved for AlxGa1 − xN for 0.12≤x≤0.42.}, number={2-4}, journal={DIAMOND AND RELATED MATERIALS}, author={Bremser, MD and Perry, WG and Zheleva, T and Edwards, NV and Nam, OH and Parikh, N and Aspnes, DE and Davis, RF}, year={1997}, month={Mar}, pages={196–201} } @article{smith_wolden_bremser_hanser_davis_lampert_1997, title={High rate and selective etching of GaN, AlGaN, and AlN using an inductively coupled plasma}, volume={71}, ISSN={["0003-6951"]}, DOI={10.1063/1.120463}, abstractNote={The etching behavior of gallium nitride (GaN), aluminum gallium nitride (AlxGa1−xN), and aluminum nitride (AlN) has been systematically examined in an inductively coupled plasma (ICP) using Cl2 and Ar as the reagents. Etch rates were strongly influenced by ICP power and dc bias, while relatively insensitive to pressure, flow rate, and gas composition. Maximum etch rates of 9800 Å/min for GaN, 9060 Å/min for Al0.28Ga0.72N, and 7490 Å/min for AlN were attained. The etch profiles were highly anisotropic over the range of conditions studied. The dc bias had to exceed certain voltages before significant etch rates were obtained. These values were <−20 V for GaN, −40 V for Al0.28Ga0.72N, and >−50 V for AlN. As such, increasing selectivity for GaN over Al0.28Ga0.72N and AlN was achieved at dc biases below −40 V. At −20 V, the GaN etch rates were 38 times greater than AlN and a factor of 10 greater than Al0.28Ga0.72N. These results demonstrate the importance of ion bombardment in the etching of these materials.}, number={25}, journal={APPLIED PHYSICS LETTERS}, author={Smith, SA and Wolden, CA and Bremser, MD and Hanser, AD and Davis, RF and Lampert, WV}, year={1997}, month={Dec}, pages={3631–3633} } @inproceedings{rossow_edwards_bremser_kern_liu_davis_aspnes_1997, title={In-plane optical anisotropies of Al(x)Ga(1-x)N films in their regions of transparency}, DOI={10.1557/proc-449-835}, abstractNote={ABSTRACT}, booktitle={III-V nitrides: symposium held December 2-6, 1996, Boston, Massachusetts, U.S.A. (Materials Research Society symposia proceedings ; v. 449)}, publisher={Pittsburgh, Pa.: Materials Research Society}, author={Rossow, U. and Edwards, N. V. and Bremser, M. D.. and Kern, R. S. and Liu, H. and Davis, R. F. and Aspnes, D. E.}, year={1997}, pages={835–840} } @article{parikh_suvkhanov_lioubtchenko_carlson_bremser_bray_davis_hunn_1997, title={Ion implantation of epitaxial GaN films: Damage, doping and activation}, volume={127}, ISSN={["0168-583X"]}, DOI={10.1016/S0168-583X(97)00076-1}, abstractNote={Monocrystalline GaN films grown on AlN buffer layers previously deposited on 6HSiC(0001) wafers and having dislocation densities on the order of 107 cm/cm3 beyond 0.5 μm from the initial growth interface have been achieved via chemical vapor deposition (CVD). The absence of low angle grain boundaries invariably extant in GaN films deposited on sapphire substrates and the relatively low dislocation densities and absence of stacking faults and twinning in the implantation regions of the films make them the best materials available for the study of implantation doping. In our initial study, 160 keV Si (n-type) and 120 keV Mg (p-type) with projected range ∼ 110 nm and fluences of 1e14, 5e14 and 1e15 cm−2 were implanted at both room temperature and 550°C. The samples were characterized by Rutherford backscattering (RBS)/channeling and photoluminescence (PL) techniques before and after implantation. RBS/channeling results of virgin and as-implanted GaN for 120 keV Mg at 550°C and 1e15 cm−2 fluence showed that even at this comparatively high dose the implantation damage is very little. However the characteristic PL signal which was present before the implantation disappeared even for the lowest dose (1e14 cm−2). These samples were annealed in a rapid thermal annealing furnace at 1000°C, and damage recovery and dopant activation were measured by PL, RBS/channeling and Cross-Sectional TEM (XTEM).}, journal={NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS}, author={Parikh, N and Suvkhanov, A and Lioubtchenko, M and Carlson, E and Bremser, M and Bray, D and Davis, R and Hunn, J}, year={1997}, month={May}, pages={463–466} } @article{nam_bremser_zheleva_davis_1997, title={Lateral epitaxy of low defect density GaN layers via organometallic vapor phase epitaxy}, volume={71}, number={18}, journal={Applied Physics Letters}, author={Nam, O.-H. and Bremser, M. D. and Zheleva, T. S. and Davis, R. F.}, year={1997}, pages={2698–2640} } @article{kaminska_piotrowska_barcz_ilka_guziewicz_kasjaniuk_dynowska_kwiatkowski_bremser_davis_1997, title={Ohmic contacts to GaN by solid-phase regrowth}, volume={92}, ISSN={["0587-4246"]}, DOI={10.12693/APhysPolA.92.819}, abstractNote={Ni/Si-based contact schemes based on the solid-phase regrowth process have been developed to form low-resistance ohmic contacts to GaN with a minimum contact resistivity of 1 x 10 -3 Ω cm2 and 1 x 10 -2 Ω cm2 to GaN:Si (n 2 x 10 17 cm-3) and GaN:Mg (p 3 x 1017 cm-3 ).The solid-phase regrowth process responsible for the ohmic contact formation was studied using X-ray diffraction, secondary ion mass spectrometry and Rutherford backscattering spectrometry.}, number={4}, journal={ACTA PHYSICA POLONICA A}, author={Kaminska, E and Piotrowska, A and Barcz, A and Ilka, L and Guziewicz, M and Kasjaniuk, S and Dynowska, E and Kwiatkowski, S and Bremser, MD and Davis, RF}, year={1997}, month={Oct}, pages={819–823} } @article{bergman_bremser_perry_davis_dutta_nemanich_1997, title={Raman analysis of the configurational disorder in AlxGa1-xN films}, volume={71}, ISSN={["0003-6951"]}, DOI={10.1063/1.119367}, abstractNote={Raman analysis of the E2 mode of AlxGa1−xN in the composition range 0⩽x⩽1 is presented. The line shape was observed to exhibit a significant asymmetry and broadening toward the high energy range. The spatial correlation model is discussed, and is shown to account for the line shape. The model calculations also indicate the lack of a long-range order in the chemical vapor deposition alloys. These results were confirmed by x-ray scattering: the relative intensity of the superlattice line was found to be negligible. The line broadening of the E2 mode was found to exhibit a maximum at a composition x≅0.5 indicative of a random disordered alloy system.}, number={15}, journal={APPLIED PHYSICS LETTERS}, author={Bergman, L and Bremser, MD and Perry, WG and Davis, RF and Dutta, M and Nemanich, RJ}, year={1997}, month={Oct}, pages={2157–2159} } @article{edwards_yoo_bremser_zheleva_horton_perkins_weeks_liu_stall_kuech_et al._1997, title={Spectral analysis of above-, below-, and near-bandedge phenomena in GaN thin films}, volume={50}, ISSN={["0921-5107"]}, DOI={10.1016/s0921-5107(97)00151-7}, abstractNote={We report spectroscopic ellipsometry (SE) and low-temperature reflectance data on epitaxial GaN thin film samples covering the widest range of tensile and compressive stress (−3.8–3.5 kbar) thus far. SE allows us to assess the preparation of smooth and abrupt GaN surfaces by chemical treatments in real time, and, coupled with the reflectance data, the E dn/dE contribution to dispersion, which is important for laser action. The reflectance data explicitly show the nonlinear behavior of the B–A and C–A splittings versus the energy of the A exciton. Lineshape ambiguities that hindered previous interpretations have been resolved with reciprocal space analysis, allowing us to obtain band parameters such as ΔSO=17.0±1 meV and ΔCF=9.8±1 meV with increased confidence.}, number={1-3}, journal={MATERIALS SCIENCE AND ENGINEERING B-SOLID STATE MATERIALS FOR ADVANCED TECHNOLOGY}, author={Edwards, NV and Yoo, SD and Bremser, MD and Zheleva, T and Horton, MN and Perkins, NR and Weeks, TW and Liu, H and Stall, RA and Kuech, TF and et al.}, year={1997}, month={Dec}, pages={134–141} } @article{sowers_christman_bremser_ward_davis_nemanich_1997, title={Thin films of aluminum nitride and aluminum gallium nitride for cold cathode applications}, volume={71}, DOI={10.1063/1.120052}, abstractNote={Cold cathode structures have been fabricated using AlN and graded AlGaN structures (deposited on n-type 6H-SiC) as the thin film emitting layer. The cathodes consist of an aluminum grid layer separated from the nitride layer by a SiO2 layer and etched to form arrays of either 1, 3, or 5 μm holes through which the emitting nitride surface is exposed. After fabrication, a hydrogen plasma exposure was employed to activate the cathodes. Cathode devices with 5 μm holes displayed emission for up to 30 min before failing. Maximum emission currents ranged from 10–100 nA and required grid voltages ranging from 20–110 V. The grid currents were typically 1 to 104 times the collector currents.}, number={16}, journal={Applied Physics Letters}, author={Sowers, A. T. and Christman, J. A. and Bremser, M. D. and Ward, B. L. and Davis, R. F. and Nemanich, R. J.}, year={1997}, pages={2289–2291} } @article{edwards_yoo_bremser_weeks_nam_davis_liu_stall_horton_perkins_et al._1997, title={Variation of GaN valence bands with biaxial stress and quantification of residual stress}, volume={70}, ISSN={["0003-6951"]}, DOI={10.1063/1.119089}, abstractNote={Low-temperature reflectance data on epitaxial GaN thin-film samples covering the widest range of tensile and compressive stress (−3.8–3.5 kbar) thus far explicitly show the nonlinear behavior of the B–A and C–A splittings versus the energy of the A exciton. Lineshape ambiguities that hindered previous interpretations have been resolved with reciprocal-space analysis, allowing us to obtain band parameters such as ΔSO=17.0±1meV with increased confidence.}, number={15}, journal={APPLIED PHYSICS LETTERS}, author={Edwards, NV and Yoo, SD and Bremser, MD and Weeks, TW and Nam, OH and Davis, RF and Liu, H and Stall, RA and Horton, MN and Perkins, NR and et al.}, year={1997}, month={Apr}, pages={2001–2003} } @inproceedings{edwards_yoo_bremser_horton_perkins_weeks_liu_stall_kuech_davis_et al._1997, title={Variation of GaN valence bands with biaxial stress: quantification of residual stress and impact on fundamental band parameters}, DOI={10.1557/proc-449-781}, abstractNote={ABSTRACT}, booktitle={III-V nitrides: symposium held December 2-6, 1996, Boston, Massachusetts, U.S.A. (Materials Research Society symposia proceedings ; v. 449)}, publisher={Pittsburgh, Pa.: Materials Research Society}, author={Edwards, N. V. and Yoo, S. D. and Bremser, M. D. and Horton, M. N. and Perkins, N. R. and Weeks, T. W. and Liu, H. and Stall, R. A. and Kuech, T. F. and Davis, R. F. and et al.}, year={1997}, pages={781–786} } @article{kisielowski_kruger_ruvimov_suski_ager_jones_lilientalweber_rubin_weber_bremser_et al._1996, title={Strain-related phenomena in GaN thin films}, volume={54}, number={24}, journal={Physical Review. B, Condensed Matter and Materials Physics}, author={Kisielowski, C. and Kruger, J. and Ruvimov, S. and Suski, T. and Ager, J. W. and Jones, E. and Lilientalweber, Z. and Rubin, M. and Weber, E. R. and Bremser, M. D. and et al.}, year={1996}, pages={17745–17753} }