Avalanche photodiodes (APDs) have been fabricated in order to determine the impact ionization coefficients of electrons (α) and holes (β) in AlxGa1−xAsySb1−y lattice matched to GaSb for three alloy compositions: (x = 0.40, y = 0.035), (x = 0.55, y = 0.045), and (x = 0. 65, y = 0.054). The impact ionization coefficients were calculated from photomultiplication measurements made on specially designed APDs, which allowed for both pure electron and pure hole injection in the same device. Photo-multiplication measurements were made at temperatures ranging from 77 K to 300 K for all three alloys. A quasi-physical model with an explicit temperature dependence was used to express the impact ionization coefficients as a function of electric-field strength and temperature. For all three alloys, it was found that α < β at any given temperature. In addition, the values of the impact ionization coefficients were found to decrease as the aluminum concentration of the AlGaAsSb alloy was increased. A value between 1.2 and 4.0 was found for β/α, which is dependent on temperature, alloy composition, and electric-field strength.
Results from a study of indirect wafer bonding and epitaxial transfer of GaSbbased materials are presented. Benzocyclobutene (BCB) was used as a bonding agent to bond GaSb and epitaxial structures lattice matched to GaSb onto Si, GaAs, and sapphire carrier substrates. To better understand sources of stress during the bonding process, which can result in cracking and subsurface damage of the GaSb-based materials, BCB's hardness and reduced elastic modulus were measured at various stages during the curing process. Based on the results of curing experiments, a bonding and epitaxial transfer process for GaSb-based materials was then developed. Following bonding, using an experimentally determined low-stress cure cycle, GaSb substrates were removed from epitaxial layers of InAsSb using a combination of mechanical thinning and polishing followed by selective chemical etching using a hydrofluoric and chromic acid solution. Etch selectivity data are also presented where selectivity greater than 100:1 is achieved for GaSb:InAsSb.
High-quality GaSb substrates with minimal surface roughness and thin, uniform oxide layers are critical for developing low-power, epitaxy-based, electronic and optoelectronic devices. Ion-beam processing techniques of gas-cluster ion beam (GCIB) and bromine ion-beam assisted etching (Br-IBAE) were investigated as to their potential for improving the suitability of substrate surfaces for molecular beam epitaxial (MBE) growth. Statistical analysis of the residual surface roughness provides insight into ion-beam processing and its impact on epitaxial growth. Images of episurfaces grown on chemical mechanical polished (CMP), Br-IBAE, and GCIB finished substrates were obtained using atomic force microscopy (AFM) and these were statistically analyzed to characterize their surface roughness properties. Autocorrelation analysis of the first two types of episurfaces showed a quick loss of correlation within ~100 nm. The episurface with Br-IBAE also showed isotropic mound roughness with sharp point-like protrusions. The GCIB prepared episurfaces exhibited the formation of uniform step-terrace patterns with monatomic steps and wide terraces as indicated by the strong, long range (>0.5 µm) correlations. Statistical analysis of the GCIB episurfaces showed self-similar random fractal behavior over eight orders of magnitude in the power spectral density (PSD) with a fractal dimension of ~2.5.
Articles you may be interested inMolecular beam epitaxy growth of high electron mobility InAs/AlSb deep quantum well structure Surface preparation and homoepitaxial deposition of AlN on (0001)-oriented AlN substrates by metalorganic chemical vapor deposition Epitaxial growth on gas cluster ion-beam processed GaSb substrates using molecular-beam epitaxy Comparison of mixed anion, InAs y P 1−y and mixed cation, In x Al 1−x As metamorphic buffers grown by molecular beam epitaxy on (100) InP substrates Noncontact atomic force microscopy ͑AFM͒ has been used to assess the surface morphology and structure of InSb homoepitaxial layers grown on chemical mechanical polished ͑CMP͒ InSb͑100͒ and InSb͑111͒B surfaces. Although it is difficult to grow epilayers on highly conducting InSb substrates, this work demonstrates the ability to grow layers with an average roughness ͑R a ͒ of 5.7 Å on 2 ϫ 10 18 n-type InSb͑100͒ surfaces. Furthermore on 7 ϫ 10 14 n-type InSb͑111͒B surfaces, extremely flat layers with R a 's of approximately 1.7 Å were grown. Thermal x-ray photoelectron spectroscopy was implemented to analyze surface oxide desorption on the CMP prepared "epiready" wafers. Sb to In flux ratio and substrate deposition temperature are critical in obtaining high quality epitaxial material. For the InSb͑100͒ surfaces, an Sb/ In flux ratio of 1.5:1, a substrate temperature of 380°C, and a background pressure of 1 ϫ 10 −10 Torr produced smooth surfaces. For InSb͑111͒B surfaces, a ratio of 7:1 and a substrate temperature of 380°C at a similar background pressure produced smooth surfaces. Higher flux ratios resulted in atomically rough surfaces. The homoepitaxy formation of an ordered step terrace surface was confirmed with AFM on both epiready CMP prepared InSb crystal surfaces.
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