Kazumi Kasai

Material and device properties of GaAs on sapphire grown by metalorganic chemical vapor deposition

Surface morphology, electron mobility, and photoluminescence (PL) spectrum have been investigated for the epitaxial layers of GaAs on (0001) sapphire grown at several temperatures. The optimum growth temperature range is determined to be around 690 °C. The mobility and the PL intensity efficiency are improved by increasing the layer thickness, due to the decrease of defect density. The structure related to the defects is located at a wavelength of 1.04 μm in the PL spectra. We fabricate the first field‐effect transistor on GaAs on sapphire, and it has a transconductance of 20 mS/mm for a gate length of 2.5 μm.

EFFECT OF THREADING DISLOCATIONS ON MOBILITY IN SELECTIVELY DOPED HETEROSTRUCTURES GROWN ON SI SUBSTRATES

We studied the effect of threading dislocation scattering on the mobility of a two‐dimensional electron gas. To verify our theory, we grew Si‐doped AlGaAs/GaAs selectively doped heterostructures with different dislocation densities by changing the number of thermal annealing cycles. The theory agreed well with our experimental results. Previous work on high electron mobility transistors (HEMTs) fabricated on Si indicated that the device characteristics are insensitive to the dislocation density. Our theory states that the room temperature mobility reduction by dislocations with a density below 108 cm−3 does not affect HEMT device performance, which is consistent with empirically known results.

Effect of strained InGaAs step bunching on mobility and device performance in n-InGaP/InGaAs/GaAs pseudomorphic heterostructures grown by metalorganic vapor phase epitaxy

We studied the surface of thin strained InGaAs layers grown on GaAs and n-GaAs/n-InGaP/InGaAs/GaAs pseudomorphic high electron mobility transistor (HEMT) structures using atomic force microscopy (AFM). We observed large step bunching from layer-by-layer growth more readily in InGaAs than in GaAs, due to strain. AsH 3 annealing of the InGaAs surface induced step bunching movement, and reduced the surface free energy and strain. We investigated the effect of the InGaAs growth conditions on the heterointerface roughness in HEMTs by selectively etching n-GaAs and n-InGaP. We found that etched InGaAs differs from as-grown InGaAs and that the electron mobility in HEMTs is insensitive to InGaAs step bunching due to both the high sheet carrier density and the large step periodicity. Increasing InGaAs growth rate causes micro-alloy clustering, although growth proceeds layer-by-layer, which affects the n-GaAs cap growth mode and degrades the mobility. Tertiarybutylarsine can suppress step bunching because of its low decomposition temperature. We also investigated the effect of substrate misorientation and found that both the mobility and the quantum well characteristics were primarily affected by step type. We fabricated HEMTs with 1 μm long gate electrodes parallel and perpendicular to the step bunching. We found that the step bunching slightly influences the K-value around the threshold voltage in HEMTs

Donor‐cation vacancy complex in Si‐doped AlGaAs grown by metalorganic chemical vapor deposition

The donor‐cation vacancy complex in Si‐doped AlGaAs grown by metalorganic chemical vapor deposition has been identified by examining the growth‐condition dependence of photoluminescence (PL) spectra. It has been revealed that the complex has the same origin as the self‐activated center in GaAs, and is relevant to the degradation of crystal quality for high doping and high V/III ratio conditions. The excitation intensity dependence of PL spectra, and the fact that the emission is not observed for the samples with indirect gaps, suggest that the emission is a band‐to‐acceptor transition. The temperature dependence of the emission intensity and linewidth are compared with GaAs.

Effective Si planar doping of GaAs by MOVPE using tertiarybutylarsine

Abstract We demonstrate highly effective Si planar doping of GaAs by atmospheric-pressure metalorganic vapor phase epitaxy (MOVPE) using tertiarybutylarsine (tBAs) as an alternative arsenic source. The Si incorporation coefficient using tBAs is always higher than that using arsine. The dependence of the Si incorporation coefficient on the group-V precursor flow rate and the gas flow velocity differs greatly between group-V precursors. This indicates that the gas phase reactions between group-V and dopant source dominate the Si doping process, regardless of group-III precursor. We applied a kinetic simulation to the pyrolysis of group-V precursors and confirmed that a large amount of AsH 2 exists in the gas phase when using tBAs. We propose that the reactions between As species radicals and silane occur, producing silylarsine (H 2 AsSiH 3 ) and that silylarsine is abundant for tBAs. Silylarsine rather than SiH 2 should be the most significant product contributing to the Si doping reactions.

MOVPE Growth of Selectively Doped AlGaAs/GaAs Heterostructures with Tertiarybutylarsine

We have used tertiarybutylarsine (tBAs) as a source alternative to AsH3 in the metalorganic vapor phase epitaxy (MOVPE) of selectively doped AlGaAs/GaAs heterostructures. A sheet carrier concentration of 9.2×1011 cm-2 and an electron mobility of 52000 cm2V-1s-1 have been obtained at 77 K for a heterostructure with a 5 nm spacer layer. This is, to our knowledge, the first demonstrated fabrication of two-dimensional electron gas with an alternative As source.

Multi-Wafer Growth of HEMT LSI Quality AlGaAs/GaAs Heterostructures by MOCVD

We report the first successful multi-wafer growth of HEMT LSI quality AlGaAs/GaAs selectively doped heterostructures by atmospheric pressure MOCVD. Highly uniform AlGaAs films with variations in thickness and doping characteristics of less than ± 2.0% and ± 1.5 %, respectively, have been grown on simultaneously revolving and rotating substrates. A trial fabrication of HEMTs resulted in threshold voltage standard deviations as small as 23 mV for E-HEMTs and 35 mV for D-HEMTs distributed over an entire two-inch wafer.

Recent progress in MOVPE for HEMT LSIs

An MOVPE technique capable of mass-producing selectively doped AlGaAs/GaAs heterostructure has been developed for HEMT LSI applications. A barrel-type reactor developed has a load capacity of twelve 3-inch wafers. Wafer rotation resulted in extremely uniform epitaxial layers. The variations in both layer thickness and carrier concentration of a Si-doped AlGaAs layer are less than ±1% across a 3-inch wafer. The wafer-to-wafer variations among the twelve wafers are ±1.1% for layer thickness and ±1.8% for carrier concentration. The reactor routinely produces high-quality AlGaAs/GaAs selectively doped heterostructures. A mobility of 121,000 cm2/V ·s with a sheet carrier concentration of 6.46×1011 cm-2 was obtained at77 K for the heterostructure having a 7-nm spacer layer. The total particle density on an epitaxial layer was reduced to less than 10 cm-2. The fabricated HEMTs showed excellent uniformity of the threshold voltage. The standard deviations were as small as 10.1 mV for E-HEMTs and 16.1 mV for D-HEMTs over an entire 3-inch wafer.

Surface Morphology and Line Fill Properties of Gold Grown by Organometallic Chemical Vapor Deposition

Dimethyl gold hexafluoroacetylacetonate, (DMAu(hfac)) was used to grow gold films by thermal decomposition. We found that surface morphology and line fill properties greatly depend on the substrate temperature and reactor pressure. Under optimum growth conditions, we have obtained gold films with flat surfaces and fine line fillings. We propose a growth model to explain the variation in surface morphology at various growth temperatures and reactor pressures.

Lateral diffusion of sources during selective growth of Si‐doped GaAs layers by metalorganic vapor phase epitaxy

Lateral diffusion of sources during selective growth of Si‐doped GaAs layers by metalorganic vapor phase epitaxy was analyzed. The diffusion lengths of gallium and silicon species were estimated from carrier concentration profiles measured by Raman spectroscopy and thickness profiles. Using the diffusion lengths obtained, it is speculated that the diffusion materials are monomethylgallium and silylarsine. From their identical diffusion lengths, it was determined that there is no difference in diffusion materials between arsine and tertiarybutylarsine.