ABSTRACTWe investigated the effect of substrate inclination and direction on the structural prope... more ABSTRACTWe investigated the effect of substrate inclination and direction on the structural properties of an InGaAs linearly compositionally graded buffer layer with a AlGaAs/InGaAs superlattice grown by molecular beam epitaxy on 2° offcut GaAs substrates. Reciprocal space maps were used to determine the relaxation and tilt of the buffer layer and superlattice with respect to each other and to the substrate. From (004) reciprocal space maps, a linear relationship between tilt and In mole fraction was observed for the buffer layer. This tilt was greatly reduced near the top of the buffer which was found to be completely strained. Interestingly, the tilt along a <110> direction was greater than that observed along the miscut axis. This may be due to the miscut axis not being parallel to a low index plane. Reciprocal space maps of asymmetric diffraction planes were used to determine the relaxation of the buffer layer as a function of In mole fraction. Along a <110> directio...
The ability to reduce contact resistances within an HBT device will greatly improve its speed and... more The ability to reduce contact resistances within an HBT device will greatly improve its speed and thus lead to a higher performance transistor. We investigated various processing improvements to enhance HBT technology using refractory metal contacts, InAs cap, and regrowth of emitter contact layers. For their high thermal stability, processing capabilities and reliability, we chose to use refractory metals such as molybdenum and tungsten as the ohmic metal contact. In comparison to InGaAs contact layer, InAs cap gave a more continuous and gave a low contact resistivity. Regrowing films provides processing advantages while increasing the resistivity only slightly.
Devices based on III-V semiconductors have generated widespread interest due to their superior pe... more Devices based on III-V semiconductors have generated widespread interest due to their superior performance over conventional semiconductors. However, III-Vs are inhibited from mass commercialization because of high costs. Thus, there is a motivation to develop affordable, high-quality thin film III-V devices, which has been realized through exfoliation techniques. In this work, a porous InP structure with optimal morphology was fabricated for exfoliation. A relationship between surface porosity and current density was determined for obtaining a desirable porous structure. Surface porosities as low as 0.02% were achieved, and it was found that reducing the porosity lowered the surface roughness. Thus, porous layers with surface roughness approaching polished InP were demonstrated. The porosities and surface roughness obtained are lower than previously reported and more ideal for growing a low-defect epitaxial film. By growing higher quality epitaxial films on a reusable seed wafer, h...
2003 International Symposium on Compound Semiconductors
We discuss the interpretation of images of α-SiC substrates and GaN layers deposited on SiC using... more We discuss the interpretation of images of α-SiC substrates and GaN layers deposited on SiC using two common variants of diffraction imaging: double crystal (reflection) topography and Lang (transmission) topography. Dependence of image resolution on layer rocking curve breadth is demonstrated, and implication for limitations imposed by thin and defective layers are discussed.
The stresses and strains developed through heterogeneous integration of semiconductor structures ... more The stresses and strains developed through heterogeneous integration of semiconductor structures represent engineering variables for which the materials limits must be addressed. The objective here is to engineer the stability of III-V and II-VI based wafer bond templates for subsequent epitaxial growth of device structures using non-compliant layers. Stress and strain are key parameters in the development of these structures. The difference in coefficients of thermal expansion between the handle substrate and the transferred and subsequently grown layers lead to high strains that can exceed critical thickness values. An empirical model is proposed to explain the experimental data for a series of different template layer / handle substrate combinations. The strain introduced during hydrogen implantation, which promotes exfoliation of a layer, also shows interesting materials-related trends, and the monitoring of the strain helps predict optimal transfer conditions. In both cases, the trends are consistent for a variety of compound semiconductor materials.
Colloidal metal nanoparticles are emerging as key materials for catalysis, plasmonics, sensing, a... more Colloidal metal nanoparticles are emerging as key materials for catalysis, plasmonics, sensing, and spectroscopy. Within these applications, control of nanoparticle shape lends increasing functionality and selectivity. Shape-controlled nanocrystals possess well-defined surfaces and morphologies because their nucleation and growth are controlled at the atomic level. An overall picture of shaped metal nanoparticles will be presented, with a particular focus on solution-based syntheses and assembly for the noble metals. General strategies for synthetic control will be discussed, emphasizing key factors that result in anisotropic, nonspherical growth such as crystallographically selective adsorbates and seeding processes. The application of such nanoparticles and their arrays in SERS will be discussed.
International Conference on Indium Phosphide and Related Materials, 2005.
ABSTRACT The rapid kinetics of strain relaxation in InxAl1-xAs graded buffer layers (GBLs) was ex... more ABSTRACT The rapid kinetics of strain relaxation in InxAl1-xAs graded buffer layers (GBLs) was exploited to produce thin (0.21 μm-0.90 μm) buffer layers graded from the InP substrate to 6.0 Å. The layers were fully relaxed, with a cross-hatched surface roughness of 4 nm, and threading dislocation densities of about 108 cm-2 for the thinnest buffer and 106 cm-2 for the 0.45 and 0.90 μm GBL structures. Identical HBT structures were grown on each of these buffers. The current gain was at least 60 with low reverse leakage currents.
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures
We investigated the effect of substrate misorientation on the structural properties of an InGaAs ... more We investigated the effect of substrate misorientation on the structural properties of an InGaAs linearly compositionally graded buffer layer and an AlGaAs/InGaAs superlattice grown by molecular‐beam epitaxy on both on‐axis and 2° miscut (001) GaAs substrates. Triple axis x‐ray diffraction and reciprocal space maps were used to determine the relaxation and tilt of the buffer layer and superlattice with respect to each other and to the substrate. A tilt of 0.17° between the buffer layer and substrate was observed from (004) reciprocal space maps of the heterostructure grown on an off‐axis substrate, while none was observed for the heterostructure grown on the on‐axis substrate. The layer tilt axis for the miscut substrate, which coincided with a 〈110〉 direction, was 32° from the miscut axis. (224) glancing exit reciprocal space maps showed the majority of the buffer layer to be relaxed, with the top portion corresponding to a strained denuded zone free of misfit segments. Intersubband measurements showed n...
Ion Beam Layer Separation of Cadmium Zinc Telluride Rabi S. Bhattacharya\ P. He\ Y. Xu^ and M. Go... more Ion Beam Layer Separation of Cadmium Zinc Telluride Rabi S. Bhattacharya\ P. He\ Y. Xu^ and M. Goorsky^ ' UES, Inc.4401 Dayton-Xenia Road, Dayton, OH 45432 ^ University of California at Los Angeles, 10920 Wilshire Blvd, Suite 107, Los Angeles CA 90024 Abstract. ...
ABSTRACTSelective cpitaxial growth during metal-organic vapor phase epitaxy (MOVPE) can be accomp... more ABSTRACTSelective cpitaxial growth during metal-organic vapor phase epitaxy (MOVPE) can be accomplished over a wide range of growth conditions through the usC of alternative growth precursors. We have used chlorine-containing growth precursors, such as diethyl gallium chloride, (C2H5)2GaCl, to selectively grow GaAs and AlxGa1x As. The growth process has been thermodynamically modelled in order to estimate relative growth rates and alloy composition. This model indicates that near the growth front the growth process is chemically similar to the inorganic-based growth of compound semiconductors. This growth technique has been applied to the growth of extremely low resistance ohmic contact structures and quantum well structures.
ABSTRACTWe have investigated the structural and electronic properties of partially strain-relaxed... more ABSTRACTWe have investigated the structural and electronic properties of partially strain-relaxed InxGal-xAs/GaAs heterojunctions, grown by molecular beam epitaxy (MBE) on both misoriented and nominally flat (001) GaAs substrates. Mobility measurements using Hall bars aligned along the [110] and [110] in-plane directions reveal an asymmetry in bulk InGaAs electron mobility. This asymmetry is correlated with an anisotropic bulk strain relaxation and interfacial misfit dislocation density, determined from high-resolution x-ray rocking curves (XRC), as well as a polarization anisotropy in cathodoluminescence (CL).
Metallorganic decomposition of metal carboxylates is used to prepare porous thin films of bismuth... more Metallorganic decomposition of metal carboxylates is used to prepare porous thin films of bismuth. The general approach is to spin coat a precursor solution, bismuth 2-ethylhexanoate in a solvent of 2-methyl-1-propanol on the substrate of interest and then pyrolyze the resulting film under conditions which evolve the organic ligands but do not melt the bismuth. The controlled release of ligands
2006 International Conference on Indium Phosphide and Related Materials Conference Proceedings, 2006
ABSTRACT In0.86Al0.14As/In0.86Ga0.14As double heterojunction bipolar transistors (DHBTs) were gro... more ABSTRACT In0.86Al0.14As/In0.86Ga0.14As double heterojunction bipolar transistors (DHBTs) were grown on InP substrates by using sub-micron 6.0 Å metamorphic graded buffer layers. Good DC and RF characteristics have been demonstrated with a current gain of 30, low base-collector reverse leakage (&lt;μA), low turn-on voltage (0.45 eV), practical breakdown voltage (∼2.5 V), and peak frequencies fT and fMAX exceeding 150 GHz. Functional circuits with complexity ranging from 20 to 1100 devices have been successfully demonstrated with power dissipation reduced by a factor of two compared to equivalent circuits designed with conventional InP technology.
ABSTRACTWe investigated the effect of substrate inclination and direction on the structural prope... more ABSTRACTWe investigated the effect of substrate inclination and direction on the structural properties of an InGaAs linearly compositionally graded buffer layer with a AlGaAs/InGaAs superlattice grown by molecular beam epitaxy on 2° offcut GaAs substrates. Reciprocal space maps were used to determine the relaxation and tilt of the buffer layer and superlattice with respect to each other and to the substrate. From (004) reciprocal space maps, a linear relationship between tilt and In mole fraction was observed for the buffer layer. This tilt was greatly reduced near the top of the buffer which was found to be completely strained. Interestingly, the tilt along a <110> direction was greater than that observed along the miscut axis. This may be due to the miscut axis not being parallel to a low index plane. Reciprocal space maps of asymmetric diffraction planes were used to determine the relaxation of the buffer layer as a function of In mole fraction. Along a <110> directio...
The ability to reduce contact resistances within an HBT device will greatly improve its speed and... more The ability to reduce contact resistances within an HBT device will greatly improve its speed and thus lead to a higher performance transistor. We investigated various processing improvements to enhance HBT technology using refractory metal contacts, InAs cap, and regrowth of emitter contact layers. For their high thermal stability, processing capabilities and reliability, we chose to use refractory metals such as molybdenum and tungsten as the ohmic metal contact. In comparison to InGaAs contact layer, InAs cap gave a more continuous and gave a low contact resistivity. Regrowing films provides processing advantages while increasing the resistivity only slightly.
Devices based on III-V semiconductors have generated widespread interest due to their superior pe... more Devices based on III-V semiconductors have generated widespread interest due to their superior performance over conventional semiconductors. However, III-Vs are inhibited from mass commercialization because of high costs. Thus, there is a motivation to develop affordable, high-quality thin film III-V devices, which has been realized through exfoliation techniques. In this work, a porous InP structure with optimal morphology was fabricated for exfoliation. A relationship between surface porosity and current density was determined for obtaining a desirable porous structure. Surface porosities as low as 0.02% were achieved, and it was found that reducing the porosity lowered the surface roughness. Thus, porous layers with surface roughness approaching polished InP were demonstrated. The porosities and surface roughness obtained are lower than previously reported and more ideal for growing a low-defect epitaxial film. By growing higher quality epitaxial films on a reusable seed wafer, h...
2003 International Symposium on Compound Semiconductors
We discuss the interpretation of images of α-SiC substrates and GaN layers deposited on SiC using... more We discuss the interpretation of images of α-SiC substrates and GaN layers deposited on SiC using two common variants of diffraction imaging: double crystal (reflection) topography and Lang (transmission) topography. Dependence of image resolution on layer rocking curve breadth is demonstrated, and implication for limitations imposed by thin and defective layers are discussed.
The stresses and strains developed through heterogeneous integration of semiconductor structures ... more The stresses and strains developed through heterogeneous integration of semiconductor structures represent engineering variables for which the materials limits must be addressed. The objective here is to engineer the stability of III-V and II-VI based wafer bond templates for subsequent epitaxial growth of device structures using non-compliant layers. Stress and strain are key parameters in the development of these structures. The difference in coefficients of thermal expansion between the handle substrate and the transferred and subsequently grown layers lead to high strains that can exceed critical thickness values. An empirical model is proposed to explain the experimental data for a series of different template layer / handle substrate combinations. The strain introduced during hydrogen implantation, which promotes exfoliation of a layer, also shows interesting materials-related trends, and the monitoring of the strain helps predict optimal transfer conditions. In both cases, the trends are consistent for a variety of compound semiconductor materials.
Colloidal metal nanoparticles are emerging as key materials for catalysis, plasmonics, sensing, a... more Colloidal metal nanoparticles are emerging as key materials for catalysis, plasmonics, sensing, and spectroscopy. Within these applications, control of nanoparticle shape lends increasing functionality and selectivity. Shape-controlled nanocrystals possess well-defined surfaces and morphologies because their nucleation and growth are controlled at the atomic level. An overall picture of shaped metal nanoparticles will be presented, with a particular focus on solution-based syntheses and assembly for the noble metals. General strategies for synthetic control will be discussed, emphasizing key factors that result in anisotropic, nonspherical growth such as crystallographically selective adsorbates and seeding processes. The application of such nanoparticles and their arrays in SERS will be discussed.
International Conference on Indium Phosphide and Related Materials, 2005.
ABSTRACT The rapid kinetics of strain relaxation in InxAl1-xAs graded buffer layers (GBLs) was ex... more ABSTRACT The rapid kinetics of strain relaxation in InxAl1-xAs graded buffer layers (GBLs) was exploited to produce thin (0.21 μm-0.90 μm) buffer layers graded from the InP substrate to 6.0 Å. The layers were fully relaxed, with a cross-hatched surface roughness of 4 nm, and threading dislocation densities of about 108 cm-2 for the thinnest buffer and 106 cm-2 for the 0.45 and 0.90 μm GBL structures. Identical HBT structures were grown on each of these buffers. The current gain was at least 60 with low reverse leakage currents.
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures
We investigated the effect of substrate misorientation on the structural properties of an InGaAs ... more We investigated the effect of substrate misorientation on the structural properties of an InGaAs linearly compositionally graded buffer layer and an AlGaAs/InGaAs superlattice grown by molecular‐beam epitaxy on both on‐axis and 2° miscut (001) GaAs substrates. Triple axis x‐ray diffraction and reciprocal space maps were used to determine the relaxation and tilt of the buffer layer and superlattice with respect to each other and to the substrate. A tilt of 0.17° between the buffer layer and substrate was observed from (004) reciprocal space maps of the heterostructure grown on an off‐axis substrate, while none was observed for the heterostructure grown on the on‐axis substrate. The layer tilt axis for the miscut substrate, which coincided with a 〈110〉 direction, was 32° from the miscut axis. (224) glancing exit reciprocal space maps showed the majority of the buffer layer to be relaxed, with the top portion corresponding to a strained denuded zone free of misfit segments. Intersubband measurements showed n...
Ion Beam Layer Separation of Cadmium Zinc Telluride Rabi S. Bhattacharya\ P. He\ Y. Xu^ and M. Go... more Ion Beam Layer Separation of Cadmium Zinc Telluride Rabi S. Bhattacharya\ P. He\ Y. Xu^ and M. Goorsky^ ' UES, Inc.4401 Dayton-Xenia Road, Dayton, OH 45432 ^ University of California at Los Angeles, 10920 Wilshire Blvd, Suite 107, Los Angeles CA 90024 Abstract. ...
ABSTRACTSelective cpitaxial growth during metal-organic vapor phase epitaxy (MOVPE) can be accomp... more ABSTRACTSelective cpitaxial growth during metal-organic vapor phase epitaxy (MOVPE) can be accomplished over a wide range of growth conditions through the usC of alternative growth precursors. We have used chlorine-containing growth precursors, such as diethyl gallium chloride, (C2H5)2GaCl, to selectively grow GaAs and AlxGa1x As. The growth process has been thermodynamically modelled in order to estimate relative growth rates and alloy composition. This model indicates that near the growth front the growth process is chemically similar to the inorganic-based growth of compound semiconductors. This growth technique has been applied to the growth of extremely low resistance ohmic contact structures and quantum well structures.
ABSTRACTWe have investigated the structural and electronic properties of partially strain-relaxed... more ABSTRACTWe have investigated the structural and electronic properties of partially strain-relaxed InxGal-xAs/GaAs heterojunctions, grown by molecular beam epitaxy (MBE) on both misoriented and nominally flat (001) GaAs substrates. Mobility measurements using Hall bars aligned along the [110] and [110] in-plane directions reveal an asymmetry in bulk InGaAs electron mobility. This asymmetry is correlated with an anisotropic bulk strain relaxation and interfacial misfit dislocation density, determined from high-resolution x-ray rocking curves (XRC), as well as a polarization anisotropy in cathodoluminescence (CL).
Metallorganic decomposition of metal carboxylates is used to prepare porous thin films of bismuth... more Metallorganic decomposition of metal carboxylates is used to prepare porous thin films of bismuth. The general approach is to spin coat a precursor solution, bismuth 2-ethylhexanoate in a solvent of 2-methyl-1-propanol on the substrate of interest and then pyrolyze the resulting film under conditions which evolve the organic ligands but do not melt the bismuth. The controlled release of ligands
2006 International Conference on Indium Phosphide and Related Materials Conference Proceedings, 2006
ABSTRACT In0.86Al0.14As/In0.86Ga0.14As double heterojunction bipolar transistors (DHBTs) were gro... more ABSTRACT In0.86Al0.14As/In0.86Ga0.14As double heterojunction bipolar transistors (DHBTs) were grown on InP substrates by using sub-micron 6.0 Å metamorphic graded buffer layers. Good DC and RF characteristics have been demonstrated with a current gain of 30, low base-collector reverse leakage (&lt;μA), low turn-on voltage (0.45 eV), practical breakdown voltage (∼2.5 V), and peak frequencies fT and fMAX exceeding 150 GHz. Functional circuits with complexity ranging from 20 to 1100 devices have been successfully demonstrated with power dissipation reduced by a factor of two compared to equivalent circuits designed with conventional InP technology.
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