@article{flock_kim_asar_kim_aspnes_2004, title={Integrated rotating-compensator polarimeter for real-time measurements and analysis of organometallic chemical vapor deposition}, volume={455}, ISSN={["0040-6090"]}, DOI={10.1016/j.tsf.2004.01.069}, abstractNote={We describe a single-beam rotating-compensator rotating-sample spectroscopic polarimeter (RCSSP) integrated with an organometallic chemical vapor deposition (OMCVD) reactor for in-situ diagnostics and control of epitaxial growth, and report representative results. The rotating compensator generates Fourier coefficients that provide information about layer thicknesses and compositions, while sample rotation provides information about optical anisotropy and therefore surface chemistry. We illustrate capabilities with various examples, including the simultaneous determination of 〈ε〉 and α10 during exposure of (001)GaAs to TMG, the heteroepitaxial growth of GaP on GaAs, and the growth of (001)GaSb with TMG and TMSb. Using a recently developed approach for quantitatively determining thickness and dielectric function of depositing layers, we find the presence of metallic Ga on TMG-exposed (001)GaAs. The (001)GaSb data show that Sb deposition is self-limiting, in contrast to expectations.}, number={2004 May 1}, journal={THIN SOLID FILMS}, author={Flock, K and Kim, SJ and Asar, M and Kim, IK and Aspnes, DE}, year={2004}, month={May}, pages={639–644} }
 @article{kim_flock_asar_kim_aspnes_2004, title={Real-time characterization of GaSb homo- and heteroepitaxy}, volume={22}, ISSN={["1071-1023"]}, DOI={10.1116/1.1771669}, abstractNote={We examine the homo- and heteroepitaxial growth of moderately thick (∼700 nm) layers of GaSb with the objectives of optimizing growth conditions and determining the initial phase of heteroepitaxy on (001)GaAs. Real-time spectroscopic ellipsometry (RTSE) data show that the (001)GaSb surface degrades immediately in excess trimethylgallium (TMG), but both (001)GaSb and As-terminated (001)GaAs surfaces are stable in trimethylantimony (TMSb). The surface-dimer contribution to the optical-anisotropy (OA) signal of (001)GaSb is small and generally masked by structural (roughness) effects, hence it is not useful for determining surface stoichometry. However, we show that laser light scattering (LLS) data do allow the V/III ratio to be fine-tuned during growth to minimize macroscopic roughness. TEM micrographs show that our GaSb/GaAs heterointerface is relatively defect-free except for the necessary local accommodation of lattice mismatch. The initial phase of heteroepitaxy on (001)GaAs occurs here as a coexistence of separate regions of GaAs and GaSb.}, number={4}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B}, author={Kim, S and Flock, KL and Asar, M and Kim, IK and Aspnes, DE}, year={2004}, pages={2233–2239} }
 @article{flock_2004, title={The simultaneous determination of n, k, and t from polarimetric data}, volume={455}, ISSN={["0040-6090"]}, DOI={10.1016/j.tsf.2004.01.022}, abstractNote={In principle the complex refractive index n+ik and the thickness t of the most recently deposited material should be simultaneously determinable from the three independent quantities |rp|2, |rs|2 and rprs* returned by polarimetric measurements. However, this goal has generally not been realized due to a lack of accuracy and signal-to-noise capabilities of present technology. By investigating the properties of the Jacobian matrix I show that the need for high accuracy is a direct consequence of the strong correlations among n, k, and t within the polarimetric parameters. Further, I show that this limitation can be circumvented by taking advantage of the spectral correlations between the refractive indices of the substrate and overlayer. As an example I determine n, k, and t independently for a 1.1 Å thick layer of GaAs deposited on a GaAs/AlGaAs/GaAs pseudo-substrate from real-time data.}, journal={THIN SOLID FILMS}, author={Flock, K}, year={2004}, month={May}, pages={349–355} }
 @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{ebert_bell_flock_aspnes_2001, title={Investigation and control of MOVPE growth by combined spectroscopic ellipsometry and reflectance-difference spectroscopy}, volume={184}, ISSN={["0031-8965"]}, DOI={10.1002/1521-396x(200103)184:1<79::aid-pssa79>3.0.co;2-b}, abstractNote={The detailed characterization of epitaxial growth by metal organic vapor phase epitaxy (MOVPE) and its closed-loop feedback control at the sample level require a combination of thin-film, near-surface, and surface-sensitive techniques to determine layer thicknesses and compositions, the composition of the most recently deposited material, and surface chemistry, respectively. These data can be obtained nondestructively by spectroscopic ellipsometry (SE) and reflectance-difference (-anisotropy) spectroscopy (RDS/RAS). We describe the first unified optical system, basically a rotating-polarizer ellipsometer (RPE) integrated within a modified commercial rotating-sample MOVPE reactor, that performs both SE and RDS simultaneously in a single optical path. We provide examples of its use, showing in particular that GaP can intermix with Si during the initial stages of heteroepitaxy, and demonstrating sample-driven closed-loop feedback control of epitaxy through the fully automatic deposition of an InxGa1—xP parabolic quantum well. These results illustrate capabilities of the presented configuration and its potential for future use.}, number={1}, journal={PHYSICA STATUS SOLIDI A-APPLIED RESEARCH}, author={Ebert, M and Bell, KA and Flock, K and Aspnes, DE}, year={2001}, month={Mar}, pages={79–87} }
 @article{ebert_bell_yoo_flock_aspnes_2000, title={In situ monitoring of MOVPE growth by combined spectroscopic ellipsometry and reflectance-difference spectroscopy}, volume={364}, ISSN={["1879-2731"]}, DOI={10.1016/S0040-6090(99)00920-7}, abstractNote={Comprehensive characterization of epitaxial growth by metal organic vapor phase epitaxy (MOVPE) requires a combination of thin-film, near-surface-, and surface-sensitive techniques to determine layer thicknesses and compositions, composition of the most recently deposited material, and surface chemistry, respectively. These data can be obtained non-destructively by spectroscopic ellipsometry (SE) and reflectance-difference (-anisotropy) spectroscopy (RDS/RAS). Here we describe the first unified optical system, basically a rotating-polarizer ellipsometer (RPE) integrated into a modified commercial rotating-sample MOVPE reactor, that performs both SE and RDS simultaneously with a single optical path. Data are obtained in parallel from 240 to 840 nm with a high-speed 16-bit photodiode array (PDA) at a repetition rate greater than 2 Hz and a precision of ±0.0001. We provide examples of its use, and show in particular that GaP intermixes with Si during the initial stages of heteroepitaxy. Capabilities of the presented configuration and its potential for future investigations are discussed.}, number={1-2}, journal={THIN SOLID FILMS}, author={Ebert, M and Bell, KA and Yoo, SD and Flock, K and Aspnes, DE}, year={2000}, month={Mar}, pages={22–27} }
 @article{bell_ebert_yoo_flock_aspnes_2000, title={Real-time optical characterization of heteroepitaxy by organometallic chemical vapor deposition}, volume={18}, ISSN={["0734-2101"]}, DOI={10.1116/1.582323}, abstractNote={Heteroepitaxy of GaP on Si(100) and GaAs(100) is investigated under organometallic chemical vapor deposition conditions using combined spectroscopic ellipsometry (SE) and non-normal-incidence reflectance-difference (-anisotropy) spectroscopy. Real-time monitoring greatly assists in identifying optimum starting surfaces for heteroepitaxy since prolonged exposure to PH3 results in roughening of Si(100) and GaAs(100) surfaces, in agreement with previous work. Real-time SE data of GaP on Si indicate that under our conditions GaP and Si interpenetrate as optically identifiable materials over the first 75 Å, suggesting that either trimethylgallium or a reaction by-product can act as a catalyst for the formation of Si{111} facets.}, number={4}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A}, author={Bell, KA and Ebert, M and Yoo, SD and Flock, K and Aspnes, DE}, year={2000}, pages={1184–1189} }
 @article{bell_ebert_yoo_flock_aspnes_2000, title={Real-time optical techniques and QMS to characterize growth in a modified commercial OMVPE reactor}, volume={29}, ISSN={["0361-5235"]}, DOI={10.1007/s11664-000-0104-6}, number={1}, journal={JOURNAL OF ELECTRONIC MATERIALS}, author={Bell, KA and Ebert, M and Yoo, SD and Flock, K and Aspnes, DE}, year={2000}, month={Jan}, pages={106–111} }