Tatsuya Ohori

Pseudomorphic n-InGaP/InGaAs/GaAs grown by MOVPE for HEMT LSIs

InGaP/InGaAs/GaAs heterostructures were grown by atmospheric pressure MOVPE. Excellent uniformity was obtained for doping concentration, thickness, and composition of the epitaxial layers by rotating the substrate and cooling the inner tube. The optimum gas switching sequence for achieving sufficient mobility and sheet carrier concentration was found. Enhancement-mode and depletion-mode HEMTs were fabricated using the very thin InGaP layer as an etching stopper layer. These are essential for the fabrication of HEMT LSI circuits. The discrete devices do not exhibit I–V collapse at low temperature. Short channel effects are negligible for gate lengths as small as 0.15 μm, owing to good carrier confinement in the pseudomorphic quantum well channel and a high aspect ratio under the thin n-InGaP layer. These advantages make InGaP/InGaAs/GaAs heterostructures well suited to HEMT LSIs applications.

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.

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.

Uniform and abrupt InGaP/GaAs selectively doped heterostructures grown by MOVPE for HEMT ICs

Abstract Uniform and abrupt Si-doped InGaP/GaAs selectively doped heterostructures are grown by atmospheric-pressure metalorganic chemical vapor deposition, and the feasibility of the material system for HEMT ICs is demonstrated for the first time. The uniformities of donor concentration and thickness of Si-doped InGaP layers are ±4.5% and ±1.5%. These values are small enough for IC applications. The mobility at 4.2 K and the two-dimensional electron gas concentration obtained from Shubnikov-De Haas oscillation measurements are 89,300 cm2/V·s and 8.9×1011 cm−2 for samples with a spacer thickness of 5.5 nm. HEMT IC structures were grown to evaluate the device characteristics. It was shown that enhancement- and depletio-mode HEMTs can be fabricated on the same wafer by selective etching technique. The characteristics of the transistors exhibit no instability at 77 K.

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.

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.

Frequency dependence of capacitance‐voltage characteristics caused by DX centers in Si‐doped AlGaAs

Capacitance of Schottky barrier diodes formed on Si‐doped AlxGa1−xAs (x>0.25) decreases as the measuring frequency increases from 1 kHz to 1 MHz at room temperature. As a result of this frequency dependence, apparent donor concentrations become smaller than the true values at a measuring frequency of 1 MHz, which is widely used for derivation of donor concentrations. This frequency dependence is caused because charging and discharging at DX centers does not follow the 1‐MHz measuring frequency even at room temperature. This result is important for characterizing n‐AlGaAs and for its applications to electronic and optical devices.

AlGaAs/GaAs and AlGaAs/InGaAs/GaAs High Electron Mobility Transistors Grown by Metalorganic Vapor Phase Epitaxy Using Tertiarybutylarsine

We demonstrate the first fabrication of AlGaAs/GaAs and pseudomorphic AlGaAs/InGaAs/GaAs high electron mobility transistors (HEMTs) grown by metalorganic vapor phase epitaxy (MOVPE) using tertiarybutylarsine (tBAs) on 3-inch GaAs substrates. In the drain current-voltage characteristics, sharp pinch-off and excellent saturation were observed for HEMTs grown using tBAs as well as using arsine. A transconductance of 324 mS/mm and the K-factor of 418 mA/V2/mm were obtained using tBAs for n-AlGaAs/GaAs HEMTs with a 0.5-µm gate, while those for n-AlGaAs/InGaAs/GaAs pseudomorphic HEMTs were 350 mS/mm and 480 mA/V2/mm. These results verify that GaAs, AlGaAs, and InGaAs layers grown using tBAs are of sufficiently high quality for HEMT applications.

Large-Area MOVPE Growth of AlGaAs/GaAs Heterostructures for HEMT LSIs

We report the large-area metalorganic vapor phase epitaxy growth of AlGaAs/GaAs heterostructures for high-electron-mobility-transistor LSI applications. We used a barrel reactor with a load capacity of twelve 3-inch wafers. Wafer rotation results in ultrauniform epitaxial layers. The variations in both layer thickness and the carrier concentration of a Si-doped AlGaAs layer are less than ±1% over an entire 3-inch wafer. Wafer-to-wafer variations among the twelve wafers are ±1.1% for layer thickness and ±1.8% for the carrier concentration. The particle density on an epitaxial layer is less than 10 cm-2.