Akinori Ubukata

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.

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.

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.

Growth of Ga0.46In0.54NyAs1-y Single Quantum Wells on InP(100) Substrate by Metalorganic Chemical Vapor Deposition.

GaInNAs has been demonstrated as a 1 eV material that is lattice-matched to GaAs. Similarly, it is expected that for GaInNAs, which is lattice-matched to InP with an In content of over 50%, a band gap from 0.7 to 0.3 eV should be achievable if a few percent N could be incorporated. A Ga0.46In0.54NyAs1-y/InP single quantum well (SQW) structure grown at a relatively high growth temperature has been attempted. Low AsH3 partial pressure appeared to enhance N incorporation. A strong photoluminescence (PL) emission was observed without post-growth annealing at the growth temperature of 650 to 680°C. For our reactor, the PL properties of GaInNAs appeared to improve for the growth pressure of 120 Torr since a narrow PL linewidth as low as 32 meV was obtained at that pressure. In the low-temperature PL measurement, blue shift was observed.

1.95-µm-wavelength InGaAs/InGaAsP Laser with Compressively Strained Quantum Well Active Layer

In this study, we demonstrate the low pressure metalorganic chemical vapor deposition growth of highly compressively strained quantum well structures with large well thickness for extending the emission wavelength of InGaAs/InGaAsP lasers. By comparing the photoluminescence characteristics of quantum wells grown at different temperatures, it is clarified that a relatively high quality quantum well layer emitting at 2.0 µ m can be obtained at a growth temperature of 650° C. At 20° C, an 880-µ m-long double quantum-well laser operating at 1.946 µ m exhibits a threshold current as low as 14.6 mA, maximum output power higher than 10 mW and external differential quantum efficiency of 18.5%. The characteristic temperature is as high as 50 K.

Surface Damage in GaInAs/GaInAsP/InP Wire Structures Prepared by Substrate-Potential-Controlled Reactive Ion Beam Etching

We investigated photoluminescence intensity dependence on the width of GaInAs/GaInAsP/InP wire structures prepared by substrate-potential-controlled reactive ion beam etching. As a result, the sidewall recombination velocity was estimated to be 2.5 ×103 cm/s under a low excitation power of approximately 1 W/cm2 (Ar+-ion laser, λ=514.5 nm) at 77 K, and was almost the same as that fabricated by wet chemical etching.

Hydrogen Chloride Gas Monitoring at 1.74 µm with InGaAs/InGaAsP Strained Quantum Well Laser

A distributed feedback laser with 1.9% compressive strain in the InGaAs/InGaAsP quantum wells is demonstrated at 1.74 µm. The characteristic temperature was 66 K, and the wavelength tuning rate was 0.016 nm/mA. A laser monitoring system of hydrogen chloride gas and the laser shows a good linear calibration curve from 10 ppm to 1% concentration of hydrogen chloride gas diluted in nitrogen. The detection limit of HCl/N2 was 0.7 ppm for the present experimental setup.

Fabrication of GaInAs/GaInAsP/InP multi-quantum-wires and -boxes by substrate-potential-controlled electron cyclotron resonance reactive ion beam etching

GaInAs/GaInAsP multi-quantum-wires and -boxes with the size of 20-30 nm and aspect ratio greater than 6 were fabricated by combining electron beam lithographt and substrate-potential-controlled electron cyclotron resonance (ECR) dry etching. The photoluminescence (PL) at 77K was observed from the buried multi-quantum wires regrown by OMVPE. The PL intensity of the multi-quantum-wire sample, normalized by the space filling factor of the active region, was 66% of that of the multi-quantum-film structure before etching, which confirms the low-damage feature of this fabrication process.

Opportunities and challenges in GaN metal organic chemical vapor deposition for electron devices

The current situation and next challenge in GaN metal organic chemical vapor deposition (MOCVD) for electron devices of both GaN on Si and GaN on GaN are presented. We have examined the possibility of increasing the growth rate of GaN on 200-mm-diameter Si by using a multiwafer production MOCVD machine, in which the vapor phase parasitic reaction is well controlled. The impact of a high-growth-rate strained-layer-superlattice (SLS) buffer layer is presented in terms of material properties. An SLS growth rate of as high as 3.46 µm/h, which was 73% higher than the current optimum, was demonstrated. As a result, comparable material properties were obtained. Next, a typical result of GaN doped with Si of 1 × 1016 cm−3 grown at the growth rate of 3.7 µm/h is shown. For high-voltage application, we need a thick high-purity GaN drift layer with a low carbon concentration, of less than 1016 cm−3. It is shown that achieving a high growth rate by precise control of the vapor phase reaction is still challenge in GaN MOCVD.

Study on AlGaN/GaN growth on carbonized Si substrate

AlGaN/GaN films were grown on carbonized Si(111) substrates, which were employed to prevent impurities such as residual Ga atoms from reacting and deteriorating the surface of Si substrates. The cleaning process for the flow channel in metal organic chemical vapor deposition (MOCVD) could effectively be eliminated by using this carbonized Si substrate, and high-quality AlGaN/GaN films were obtained.