@article{kirste_wagner_schulze_strittmatter_collazo_sitar_alevli_dietz_hoffmann_2010, title={Optical properties of InN grown on templates with controlled surface polarities}, volume={207}, ISSN={["1862-6300"]}, DOI={10.1002/pssa.201026086}, abstractNote={Abstract}, number={10}, journal={PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE}, author={Kirste, Ronny and Wagner, Markus R. and Schulze, Jan H. and Strittmatter, Andre and Collazo, Ramon and Sitar, Zlatko and Alevli, Mustafa and Dietz, Nikolaus and Hoffmann, Axel}, year={2010}, month={Oct}, pages={2351–2354} }
 @article{narayanan_mahajan_bachmann_woods_dietz_2002, title={Antiphase boundaries in GaP layers grown on (001) Si by chemical beam epitaxy}, volume={50}, ISSN={["1359-6454"]}, DOI={10.1016/S1359-6454(01)00408-6}, abstractNote={We have investigated the origin of contrast features observed in coalesced GaP islands, deposited by chemical beam epitaxy on (001) Si, by high resolution transmission electron microscopy and conventional dark field electron microscopy. Our results indicate that these features are antiphase boundaries (APBs) lying on {110} planes. Image simulations have been performed to show that APBs can only be seen under specific defocus conditions in high resolution lattice images. The observed contrast is attributed to the presence of Ga–Ga and P–P wrong bonds at APBs. A model is proposed to show that the coalescence of GaP islands on the same Si terrace may not produce APBs, and the formation of such boundaries may require the presence of monoatomic steps, separating the coalescing islands.}, number={6}, journal={ACTA MATERIALIA}, author={Narayanan, V and Mahajan, S and Bachmann, KJ and Woods, V and Dietz, N}, year={2002}, month={Apr}, pages={1275–1287} }
 @article{blickle_flock_dietz_aspnes_2002, title={Pseudodielectric function of ZnGeP2 from 1.5 to 6 eV}, volume={81}, ISSN={["0003-6951"]}, DOI={10.1063/1.1492022}, abstractNote={We report pseudodielectric function data 〈ε〉=〈εa1〉+i〈εa2〉 and 〈ε〉=〈εc1〉+i〈εc2〉 for the optically uniaxial material ZnGeP2, critical point energies of structures in these data, and dielectric function data for the natural oxide. Annealing reduces the values of the peaks of 〈εa2〉.}, number={4}, journal={APPLIED PHYSICS LETTERS}, author={Blickle, V and Flock, K and Dietz, N and Aspnes, DE}, year={2002}, month={Jul}, pages={628–630} }
 @article{narayanan_mahajan_bachmann_woods_dietz_2002, title={Stacking faults and twins in gallium phosphide layers grown on silicon}, volume={82}, ISSN={["0141-8610"]}, DOI={10.1080/01418610110082034}, abstractNote={Abstract The coalescence of GaP islands, grown on Si(001), Si(111), Si(110) and Si(113) surfaces by chemical beam epitaxy, has been investigated by high-resolution transmission electron microscopy. Stacking faults and first-order twins are observed within islands before coalescence and result from stacking errors during growth on the smaller P-terminated {111} facets of GaP islands. Upon island coalescence, complex moire fringes are observed contiguous to highly faulted {111} planes within epitaxial layers grown on all four Si substrate orientations and are attributed to multiple twinning. Second-and third-order twins are also observed within (111) and (110) layers and their formation is attributed to successive twinning on differently inclined {111} facets. Amongst the four orientations, coalesced growths on the Si(111) surface are the most defective and this may be caused by a higher density of P-terminated {111} facets on islands grown on the Si(111) surface.}, number={4}, journal={PHILOSOPHICAL MAGAZINE A-PHYSICS OF CONDENSED MATTER STRUCTURE DEFECTS AND MECHANICAL PROPERTIES}, author={Narayanan, V and Mahajan, S and Bachmann, KJ and Woods, V and Dietz, N}, year={2002}, month={Mar}, pages={685–698} }
 @article{dietz_beeler_schmidt_tran_2001, title={Surface reaction kinetics of Ga1-xInxP growth during pulsed chemical beam epitaxy}, volume={178}, ISSN={["1873-5584"]}, DOI={10.1016/S0169-4332(01)00302-6}, abstractNote={The understanding of thin film growth processes and their control requires the development of surface-sensitive real-time optical characterization techniques that are able to provide insight into the surface reaction kinetics during an organometallic deposition process. These insights will allow us to move the control point closer to the point where the growth occurs, which in a chemical beam epitaxy (CBE) process is a surface reaction layer (SRL), built up of physisorbed and chemisorbed precursor fragments between the ambient and film interface. This contribution presents results on parameter estimations of rate constants and optical response factors in a reduced order surface kinetics (ROSK) model, which has been developed to describe the decomposition and growth kinetics of the involved organometallic precursors and their incorporation in the film deposition. As a real-time characterization technique, we applied p-polarized reflectance spectroscopy (PRS) during low temperature growth of epitaxial Ga1−xInxP heterostructures on Si(0 0 1) substrates by pulsed chemical beam epitaxy (PCBE). The high surface sensitivity of PRS allows us to follow alterations in composition and thickness of the SRL as they are encountered during periodic precursor supply. The linkage of the PRS response to the ROSK model provides the base for the parameter estimation, giving insights into the organometallic precursor decomposition and growth kinetics.}, number={1-4}, journal={APPLIED SURFACE SCIENCE}, author={Dietz, N and Beeler, SC and Schmidt, JW and Tran, HT}, year={2001}, month={Jul}, pages={63–74} }
 @article{dimmock_madarasz_dietz_bachmann_2001, title={Theoretical analysis of phase-matched second-harmonic generation and optical parametric oscillation in birefringent semiconductor waveguides}, volume={40}, ISSN={["2155-3165"]}, DOI={10.1364/AO.40.001438}, abstractNote={We analyze the phase-matching conditions for second-harmonic generation (SHG) and optical parametric oscillation (OPO) in birefringent nonlinear semiconductor waveguides and apply these results to the model system of ZnGeP2 on a GaP substrate. The analyses and numerical results show that phase matching can be achieved for OPO and SHG for reasonable guide thicknesses throughout much of the infrared, indicating significant potential applications for nonlinear birefringent waveguides. For the fundamental mode of a relatively thick guide the region of phase matching and the phase-matching angles are similar to those in bulk material. However, the waveguide has the added flexibility that phase-matched coupling can occur between the various modes of the guide. For example, the phase-matching region for SHG can be considerably extended by coupling the pump into the guide in the fundamental, m = 0, mode and phase matching to the m = 2 mode of the second harmonic. Significantly, the results indicate, among other things, that ZnGeP2 waveguides with harmonic output in the m = 2 mode can be used for efficient SHG from input radiation in the 9.6-10.6-microm region where bulk efficiencies in this wavelength range are too small to be useful.}, number={9}, journal={APPLIED OPTICS}, author={Dimmock, JO and Madarasz, FL and Dietz, N and Bachmann, KJ}, year={2001}, month={Mar}, pages={1438–1441} }
 @article{narayanan_mahajan_sukidi_bachmann_woods_dietz_2000, title={Orientation mediated self-assembled gallium phosphide islands grown on silicon}, volume={80}, ISSN={["0141-8610"]}, DOI={10.1080/01418610008212068}, abstractNote={Abstract Evolution of gallium phosphide epitaxial islands, grown on the (001), (111), (110) and (113) surfaces of Si by chemical beam epitaxy, has been investigated by p-polarized reflectance spectroscopy, transmission electron microscopy and atomic force microscopy. The growth nucleates as faceted three-dimensional islands on the (001) and (111) Si surfaces because of the polar nature of the heterointerface which increases the interfacial energy. A more two-dimensional-like growth mode is seen on the (110) and (113) surfaces which is attributed to the absence of charge build up at the GaP—Si heterointerface for these orientations, thereby reducing the interface energy. Islands grown on (001) Si become more faceted and larger in size with increase in growth temperature. This is due to a lower incubation time and enhanced atomic mobility at high temperatures. Wurtzite GaP has been observed to coexist with the zincblende polytype in some of the islands grown on (111) Si at 560°C. Arguments have been developed to rationalize these observations.}, number={3}, journal={PHILOSOPHICAL MAGAZINE A-PHYSICS OF CONDENSED MATTER STRUCTURE DEFECTS AND MECHANICAL PROPERTIES}, author={Narayanan, V and Mahajan, S and Sukidi, N and Bachmann, KJ and Woods, V and Dietz, N}, year={2000}, month={Mar}, pages={555–572} }
 @article{woods_dietz_ito_lauko_2000, title={Real-time thickness and compositional control of Ga1-xInxP growth using p-polarized reflectance}, volume={18}, ISSN={["0734-2101"]}, DOI={10.1116/1.582469}, abstractNote={Advances in the engineering and design of advanced electro-optical materials require sensors and control strategies that allow tight control over thickness and composition of multilayered structures. In response to this demand, we developed and applied p-polarized reflectance (PR) for real-time optical characterization and control of heteroepitaxial GaP/GaInP growth under pulsed chemical beam epitaxy conditions. For closed-loop control, we applied nonlinear control algorithms (based on nonlinear Kalman filtering) that utilizes the PR signals to adjust the source flows involved in the heteroepitaxial growth of Ga1−xInxP on Si(001). A reduced order surface kinetics model has been formulated to establish the linkage between the surface reaction kinetic and its optical response. These data are linked to compute the compositional and thickness change per time unit, utilizing the monitored PR signals for validation. This allows the establishment of feedback control algorithms, able to control both the growth rate and composition of Ga1−xInxP heterostructures.}, number={4}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A-VACUUM SURFACES AND FILMS}, author={Woods, V and Dietz, N and Ito, K and Lauko, I}, year={2000}, pages={1190–1195} }
 @article{madarasz_dimmock_dietz_bachmann_2000, title={Sellmeier parameters for ZnGaP2 and GaP}, volume={87}, ISSN={["0021-8979"]}, DOI={10.1063/1.372050}, abstractNote={Sellmeier parameters are determined for the birefringent material ZnGaP2 and the singly refractive material GaP by the minimization of chi-square employing the Levenberg–Marquardt method. The distinguishing feature of the present work is that all five Sellmeier parameters are treated as adjustable. In previous work the Sellmeier parameter related to the restrahlen frequency was fixed and set equal for both ordinary and extraordinary waves in the birefringent material. The fitted results show there is approximately an 8% difference between the two. Taking this parameter as adjustable allows for a better fit on all other parameters.}, number={3}, journal={JOURNAL OF APPLIED PHYSICS}, author={Madarasz, FL and Dimmock, JO and Dietz, N and Bachmann, KJ}, year={2000}, month={Feb}, pages={1564–1565} }
 @article{madarasz_dimmock_dietz_bachmann_2000, title={Sellmeier parameters for ZnGaP2 and GaP (vol 87, pg 1564, 2000)}, volume={87}, ISSN={["0021-8979"]}, DOI={10.1063/1.373029}, number={10}, journal={JOURNAL OF APPLIED PHYSICS}, author={Madarasz, FL and Dimmock, JO and Dietz, N and Bachmann, KJ}, year={2000}, month={May}, pages={7597–7597} }
 @article{dietz_woods_ito_lauko_1999, title={Real-time optical control of Ga1-xInxP film growth by p-polarized reflectance}, volume={17}, ISSN={["1520-8559"]}, DOI={10.1116/1.581811}, abstractNote={The engineering of advanced optoelectronic integrated circuits implies the stringent control of thickness and composition. These demands led to the development of surface-sensitive real-time optical sensors that are able to move the control point close to the point where the growth occurs, which in a chemical beam epitaxy process is the surface reaction layer, built up of physisorbed and chemisorbed precursor fragments between the ambient and film interface. In this context, we explored the application of p-polarized reflectance spectroscopy (PRS) for real-time monitoring and control of pulsed chemical beam epitaxy during low-temperature growth of epitaxial Ga1−xInxP heterostructures on Si(001) substrates. A reduced order surface kinetics model has been developed to describe the decomposition and growth kinetics of the involved organometallic precursors and their incorporation in the film deposition. We demonstrate the linkage of the PRS response towards the surface reaction chemistry, composition, film growth rate, and film properties. Mathematical control algorithms are applied that link the PR signals to the growth process control parameters to control the composition and growth rate of epitaxial Ga1−xInxP heterostructures.}, number={4}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A}, author={Dietz, N and Woods, V and Ito, K and Lauko, I}, year={1999}, pages={1300–1306} }
 @article{beeler_tran_dietz_1999, title={Representation of GaP formation by a reduced order surface kinetics model using p-polarized reflectance measurements}, volume={86}, ISSN={["1089-7550"]}, DOI={10.1063/1.370783}, abstractNote={This contribution presents results on the parameter estimation of rate constants and optical response factors in a reduced order surface kinetics (ROSK) model, which has been developed to describe the decomposition kinetics of the organometallic precursors involved and their incorporation into the film deposition. As a real-time characterization technique, we applied p-polarized reflectance spectroscopy (PRS) during low temperature growth of epitaxial GaP heterostructures on Si(001) substrates by pulsed chemical beam epitaxy. The high surface sensitivity of PRS allows us to follow alterations in the composition and thickness of the surface reaction layer as they are encountered during periodic precursor supply. Linkage of the PRS response to the ROSK model provides the base for the parameter estimation of the reduced order surface kinetics model, giving insights into the organometallic precursor decomposition and growth kinetics.}, number={1}, journal={JOURNAL OF APPLIED PHYSICS}, author={Beeler, S and Tran, HT and Dietz, N}, year={1999}, month={Jul}, pages={674–682} }
 @misc{narayanan_sukidi_hu_dietz_bachmann_mahajan_shingubara_1998, title={Growth of gallium phosphide layers by chemical beam epitaxy on oxide patterned (001)silicon substrates}, volume={54}, ISSN={["0921-5107"]}, DOI={10.1016/s0921-5107(98)00169-x}, abstractNote={GaP layers grown by chemical beam epitaxy in [110] channels fabricated on oxide-patterned (001)silicon substrates have been examined in cross-section by conventional and high resolution transmission electron microscopy. Results indicate that the layers are single crystalline. For the imaging conditions used, [110] cross-sectional micrographs show that growths in contact with the oxide exhibit twinning on one edge-on variant, whereas faults or twins are observed on two such variants in the layers which nucleate on the silicon substrate. Arguments for rationalizing these observations are developed, and their implications to improve the quality of the layer by confining faults or twins by the oxide sidewall are discussed.}, number={3}, journal={MATERIALS SCIENCE AND ENGINEERING B-SOLID STATE MATERIALS FOR ADVANCED TECHNOLOGY}, author={Narayanan, V and Sukidi, N and Hu, CM and Dietz, N and Bachmann, KJ and Mahajan, S and Shingubara, S}, year={1998}, month={Jun}, pages={207–209} }
 @article{aspnes_dietz_1998, title={Optical approaches for controlling epitaxial growth}, volume={130}, ISSN={["1873-5584"]}, DOI={10.1016/s0169-4332(98)00085-3}, abstractNote={Optical spectroscopy of surface and near-surface regions has advanced to the stage where detailed measurements can be made and analyzed in real time. Here, we discuss reported and potential applications of optical probes for sample-driven closed-loop feedback control of semiconductor epitaxy. Parameters that have been controlled include temperature, thickness in both deposition and etching, and composition, including continuously graded compositions. Although considerable progress has been made, much remains to be done before these techniques become viable production tools.}, number={1998 June}, journal={APPLIED SURFACE SCIENCE}, author={Aspnes, DE and Dietz, N}, year={1998}, month={Jun}, pages={367–376} }
 @article{bachmann_sukidi_hopfner_harris_dietz_tran_beeler_ito_banks_1998, title={Real-time monitoring of steady-state pulsed chemical beam epitaxy by p-polarized reflectance}, volume={183}, ISSN={["0022-0248"]}, DOI={10.1016/s0022-0248(97)00410-7}, abstractNote={The structure in the p-polarized reflectance (PR) intensity Rp4(t) - observed under conditions of pulsed chemical beam epitaxy (PCBE) - is modeled on the basis of the four-layer stack: ambient/surface reaction layer (SRL)/epilayer/substrate. Linearization of the PR intensity with regard to the phase factor associated with the SRL results in a good approximation that can be expressed as Rp4 = Rp3 + ΔRp.Rp3 is the reflectivity of the three-layer stack ambient-epilayer-substrate. ΔRp describes the properties of the SRL. An explicit relation is derived between ΔRp(t) and the time-dependent surface concentrations ch(t) (h = 1, 2, …, N) of the constituents of the SRL, which holds for conditions of submonolayer coverage of the surface by source vapor molecules. Under conditions of low temperature PCBE at high flux, the SRL is expected to exhibit nonideal behavior, mandating replacement of the surface concentrations by activities. Also, in this case, the thickness of the SRL must be represented in terms of partial molar volumina Vh. Since the relation between ΔRp(t) and the activities of reactants, intermediates and products of the chemical reactions driving heteroepitaxial growth is non-linear, the extraction of kinetic parameters from the measured time dependence of the PR signal generally requires numerical modeling.}, number={3}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Bachmann, KJ and Sukidi, N and Hopfner, C and Harris, C and Dietz, N and Tran, HT and Beeler, S and Ito, K and Banks, HT}, year={1998}, month={Jan}, pages={323–337} }
 @article{dietz_ito_1998, title={Real-time optical characterization of GaP heterostructures by p-polarized reflectance}, volume={313}, ISSN={["0040-6090"]}, DOI={10.1016/S0040-6090(97)00896-1}, abstractNote={The stringent tolerances in the engineering of advanced optoelectronic integrated circuits with respect to control thickness and composition of ultra-thin layers require the development of monitoring and control techniques that follow the deposition process with sub-monolayer resolution. These demands led to the development of surface-sensitive real-time optical sensors that are able to move the control point close to the point where the growth occurs, which in a chemical beam epitaxy process is the surface reaction layer, built up of physisorbed and chemisorbed precursor fragments between the ambient and film interface. In this contribution, we explore the application of p-polarized reflectance spectroscopy (PRS) in the context of real-time monitoring and control of pulsed chemical beam epitaxy (PCBE) during low temperature growth of epitaxial GaP heterostructures on Si(001) substrates by PCBE. The effect of periodic alterations in composition and thickness of a surface reaction layer (SRL) is monitored by PRS as a periodic modulated reflectance amplitude, denoted as fine structure. Using a `reduced order kinetic model' we demonstrate the linkage of the PRS response towards surface reaction chemistry, film growth rate, and film properties. Mathematical control algorithms are introduced that link the PR signals to the growth process control parameters.}, journal={THIN SOLID FILMS}, author={Dietz, N and Ito, K}, year={1998}, month={Feb}, pages={614–619} }
 @article{bachmann_hopfner_sukidi_miller_harris_aspnes_dietz_tran_beeler_ito_et al._1997, title={Molecular layer epitaxy by real-time optical process monitoring}, volume={112}, DOI={10.1016/S0169-4332(96)00975-0}, abstractNote={In this paper we consider modern methods of optical process monitoring and control in the context of atomic layer epitaxy. One specific method, p-polarized reflectance spectroscopy (PRS), is chosen to assess details of layer-by-layer growth. We show that PRS monitoring under conditions of steady-state growth by pulsed chemical beam epitaxy (PCBE) can achieve the deposition of molecular layers of GaP on silicon (100) deposited with a precision of 5%, which can be improved by reducing the growth rate and increasing the period of time averaging of the reflectance data. Since in the nucleation period prior to formation of a contiguous heteroepitaxial film inhomogeneous surface chemistry and roughening complicates the modeling of the overgrowth process, advances in both experimental methods and theory are required for extending the control to non-steady-state growth conditions. Results of simultaneous single-wavelength PR monitoring and laser light scattering measurements in conjunction with atomic force microscopy studies of short period heteroepitaxial overgrowth processes are presented. The extension of PRS to the monitoring of organometallic chemical vapor deposition at higher pressures is also discussed.}, number={1997 Mar.}, journal={Applied Surface Science}, author={Bachmann, K. J. and Hopfner, C. and Sukidi, N. and Miller, A. E. and Harris, C. J. and Aspnes, D. E. and Dietz, N. A. and Tran, Hien and Beeler, S. C. and Ito, K. and et al.}, year={1997}, pages={38–47} }
 @inproceedings{aspnes_dietz_rossow_bachmann_1997, title={Multilevel approaches toward monitoring and control of semiconductor epitaxy}, DOI={10.1557/proc-448-451}, abstractNote={Abstract}, booktitle={Control of semiconductor surfaces and interfaces: Symposium held December 2-5, 1996, Boston, Massachusetts, U.S.A. (Materials Research Society Symposium proceedings, no. 448)}, publisher={Pittsburgh, PA: Materials Research Society}, author={Aspnes, D. E. and Dietz, N. and Rossow, U. and Bachmann, K. J.}, year={1997}, pages={451–462} }
 @article{dietz_sukidi_harris_bachmann_1997, title={Real-time monitoring of surface processes by p-polarized reflectance}, volume={15}, ISSN={["0734-2101"]}, DOI={10.1116/1.580712}, abstractNote={Understanding surface chemistry under steady-state epitaxial growth involving organo-metallic chemical precursor molecules is essential for optimizing growth processes. Surface-sensitive optical real-time sensor techniques are very well suited for this task as their applications are not limited to a high vacuum environment. In this article we report the combined application of the optical sensor techniques p-polarized reflectance (PR) and laser light scattering for the real-time monitoring of low temperature growth of epitaxial GaP/GaxIn1−xP heterostructures on Si(001) and GaAs(001) substrates by pulsed chemical beam epitaxy. The high surface sensitivity of PR allows to follow growth processes with submonolayer resolution during the sequential precursor exposure of the surface that causes periodic alterations in composition and thickness of a surface reaction layer (SRL), the effect of which is monitored by PR as a periodic fine structure. This fine structure is superimposed on interference oscillations, resulting from back reflection at the substrate-layer interface with increasing layer thickness. In a linear approximation of the complex four-layer stack reflectance amplitude RR4 in the phase factor Φ1, the optical response to the SRL is formulated as an additive term in the three-layer model that describes the underlying film growth process. Analytical expressions for the first derivative of the PR signal are presented and discussed with respect to the time scale of observation that allows the separation of film growth induced changes from SRL effects. The amplitude modulation and the turning points in the fine structure are assessed and compared to experimental results, showing that an average complex dielectric function of an ultrathin SRL can be quantified, independent of surface coverage.}, number={3}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A-VACUUM SURFACES AND FILMS}, author={Dietz, N and Sukidi, N and Harris, C and Bachmann, KJ}, year={1997}, pages={807–815} }
 @misc{bachmann_dietz_miller_1996, title={Methods for monitoring and controlling deposition and etching using p-polarized reflectance spectroscopy}, volume={5552327}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Bachmann, K. J. and Dietz, N. and Miller, A. E.}, year={1996} }