Koh Matsumoto

AN ANALYSIS OF TEMPERATURE DEPENDENT PHOTOLUMINESCENCE LINE SHAPES IN INGAN

Photoluminescence (PL) line shapes in InGaN multiple quantum well structures have been studied experimentally and theoretically between 10 and 300 K. The higher temperature PL spectra can be fitted quantitatively with a thermalized carrier distribution and a broadened joint-density-of-states. The low temperature PL line shapes suggest that carriers are not thermalized, as a result of localization by band-gap fluctuations. We deduce a localization energy of ∼7 meV as compared with an activation energy of ∼63 meV from thermal quenching of the PL intensity. We thus conclude that this activation energy and the band-gap fluctuation most likely have different origins.

Uniform Growth of AlGaN/GaN High Electron Mobility Transistors on 200 mm Silicon (111) Substrate

Crack-free AlGaN/GaN high-electron-mobility transistors (HEMTs) grown on a 200 mm Si substrate by metal–organic chemical vapor deposition (MOCVD) is presented. As grown epitaxial layers show good surface uniformity throughout the wafer. The AlGaN/GaN HEMT with the gate length of 1.5 µm exhibits a high drain current density of 856 mA/mm and a transconductance of 153 mS/mm. The 3.8-µm-thick device demonstrates a high breakdown voltage of 1.1 kV and a low specific on-resistance of 2.3 mΩ cm2 for the gate–drain spacing of 20 µm. The figure of merit of our device is calculated as 5.3×108 V2 Ω-1 cm-2.

Quantum chemical study of parasitic reaction in III-V nitride semiconductor crystal growth

We have discussed the gas-phase parasitic reactions in M(CH3)3/H2/NH3 systems following the elimination of methane by carrying out ab initio quantum chemical calculations, where M denotes Al, Ga, or In. It is clearly shown that the Al source gases enhance reactivity, and the adduct-derived chain compounds grow successively with high exothermicity. We have concluded that the strong Al–N coordination interaction contributes remarkably to the stabilization of the reaction system. In the presence of excess ammonia, we have proved that potential energy barrier of the methane elimination is reduced considerably. The methane elimination by reaction of carrier H2 gas with M(CH3)3 is also exothermic.

Normally-OFF Al2O3/AlGaN/GaN MOS-HEMT on 8 in. Si with Low Leakage Current and High Breakdown Voltage (825 V)

We report recessed-gate Al2O3/AlGaN/GaN normally-OFF metal–oxide–semiconductor high-electron-mobility transistors (MOS-HEMTs) on 8 in. Si. The MOS-HEMTs showed a maximum drain current of 300 mA/mm with a high threshold voltage of +2.4 V. The quite low subthreshold leakage current (~10−8 mA/mm) yielded an excellent ON/OFF current ratio (9 × 108) with a small, stable subthreshold slope of 74 mV/dec. An atomic-layer-deposited Al2O3 layer effectively passivates, as no significant drain current dispersions were observed. A high OFF-state breakdown voltage of 825 V was achieved for a device with a gate-to-drain distance of 20 µm at a gate bias of 0 V.

Deep emission band at GaInP/GaAs interface

We have investigated the 1.46 eV deep emission band observed in the photoluminescence (PL) spectra of 100-A-thick GaAs/Ga0.52In0.48P single quantum wells grown by metal-organic vapor-phase epitaxy. We have found that the application of GaP layers at both lower and upper GaAs/Ga0.52In0.48P interface is necessary to achieve 1.52 eV emission from the well; otherwise only the deep emission band at 1.46 eV is observed in the 77 K PL spectrum. Time-resolved PL and temperature-dependent PL measurements show that the 1.46 eV deep emission is due to recombination of electrons in the conduction band of Ga0.52In0.48P and holes bound to acceptors in GaAs at the GaAs/Ga0.52In0.48P interface, which forms type-II band alignment. We propose that the application of GaP layers modifies the band alignment from type II to type I, and makes the emission from the well observable.

Flow patterns in various vertical reactors and movpe growth

Abstract Flow pattern visualization experiments and MOVPE growth have been carried out on vertical reactors. Turbulences were observed at the conically expanding region and around the injection nozzle, even if the susceptor was cold. The rules of the design of a laminar flow reactor are given. Differences in the growth of GaAs by MOVPE between a laminar flow and a turbulent flow are described. High purity GaAs layer with an electron mobiltiy at 77 K of 140,000 cm 2 /Vs at an electron concentration of 1 × 10 14 cm −3 and single quantum wells as thin as 27 A were successfully grown employing the laminar flow vertical reactor.

Quantum chemical mechanism in parasitic reaction of AlGaN alloys formation

The mechanism of parasitic reactions among trimethylaluminum (TMA), trimethylgallium (TMG), and NH3 in atmospheric pressure (AP) MOVPE for growth of AlGaN is theoretically studied using the quantum chemical method. The calculations show that metal–nitrogen chain growth reaction easily proceeds through the successive reactions of ‘complex formation with NH3’ and ‘CH4 elimination by the bimolecular mechanism’. Additionally, a parasitic reaction in APMOVPE using other raw material is also investigated. The calculated result shows that small change of raw material raises activation energy of parasitic reaction, and, thus, the parasitic reaction is suppressed. This result suggests a way to improve APMOVPE by a suitable choice of substituent.

Quantum Chemical Studies of Gas Phase Reactions between TMA, TMG, TMI and NH3

The parasitic reactions among trimethylaluminum (TMA), trimethylgallium (TMG), and NH3 obstruct the growth of AlGaN alloys in atmospheric pressure (AP) MOVPE. In this paper, we present quantum chemical calculations for the reaction of M(CH3)3 + NH3 systems (M = Al, Ga, and In for TMA, TMG, and TMI, respectively) in the gas phase. The calculations show that TMA helps the parasitic reactions to progress by orbital interaction effect. The detailed energetics and the possible reaction mechanisms of the parasitic reaction processes are discussed.

Characteristics dependence on confinement structure and single-mode operation in 2-μm compressively strained InGaAs-lnGaAsP quantum-well lasers

The optimum confinement layer structure in 2-/spl mu/m compressively strained InGaAs-InGaAsP lasers is experimentally studied. Beside the carrier overflow and absorption loss in the confinement layers, the intervalence band absorption and/or Auger recombination play an important role in laser characteristics. More attention should be paid to the confinement structure to reduce the carrier density. We obtained a better laser performance with an energy difference between the bandgap of the optical confinement layer and the laser transition energy of 280-300 meV. A distributed-feedback (DFB) laser operating at 2.043 /spl mu/m has been realized with the threshold current as low as 6 mA and the maximum output power of 6 mW. The differential quantum efficiency and the characteristic temperature are 16% and 59 K, respectively.

Highly uniform growth in a low-pressure MOVPE multiple wafer system

Abstract A novel horizontal metal organic vapor phase epitaxy (MOVPE) system, which is capable of handling six 3 inch wafers or eighteen 2 inch wafers mounted on a 10 inch diameter susceptor, has been developed for the growth of III–V compound semiconductors. The characteristic features in this system are “triple flow channel” gas injection and “face-down” wafer setting configuration. The inlet for the source gas flow is divided into three zones (upper, middle and lower flows for hydrides, organometals and hydrogen, respectively) to control the concentration boundary layer and the growth area. The wafers are placed inversely to prevent thermal convection and particles on the growing surface. The independent controlled three-part heating system is also adopted to achieve a uniform temperature distribution over an 8 inch growing surface. The thickness and the doping of GaAs, Al 0.3 Ga 0.7 As, In 0.48 Ga 0.52 P and In 0.2 Ga 0.8 As grown by this system are uniform within ± 2% over all 3 inch wafers.