@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{beeler_tran_banks_2000, title={Feedback control methodologies for nonlinear systems}, volume={107}, ISSN={["0022-3239"]}, DOI={10.1023/A:1004607114958}, abstractNote={A number of computational methods have been proposed in the literature to design and synthesize feedback controls when the plant is modeled by nonlinear dynamics. However, it is not immediately clear which is the best method for a given problem; this may depend on the nature of the nonlinearities, size of the system, whether the amount of control used or time needed for the method is a concern, and other factors. In this paper, a comprehensive comparison study of five methods for the synthesis of nonlinear control systems is carried out. The performance of the methods on several test problems are studied, and some recommendations are made as to which feedback control method is best to use under various conditions.}, number={1}, journal={JOURNAL OF OPTIMIZATION THEORY AND APPLICATIONS}, author={Beeler, SC and Tran, HT and Banks, HT}, year={2000}, month={Oct}, pages={1–33} }
 @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} }
 @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{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} }