Kunihiko Kodama

Two-Dimensional Electron Gas at GaAs/Ga0.52In0.48P Heterointerface Grown by Chloride Vapor-Phase Epitaxy

We report the first observation of two-dimensional electron gas at GaAs/Ga0.52In0.48P heterointerfaces using the Shub-nikov-de Haas measurements. The heterostructures were prepared by chloride vapor-phase epitaxy. The sheet carrier concentration is higher than that in GaAs/n-AlxGa1-xAs heterostructures with a similar donor-concentration in n-AlxGa1-xAs layers. This may be attributed to the facts that the dominant donors in the Ga0.52In0.48P layers are shallow and that the conduction-band discontinuity at the GaAs/Ga0.52In0.48P interfaces is large.

Energy-Band Offset of In0.53Ga0.47As–In0.52(Ga1-xAIx)0.48As Heterostructures, Determined by Photoluminescenee Excitation Spectroscopy of Quasi-Parabolie Quantum Wells Grown by MBE

The conduction-band discontinuity, ΔEc(x), of In0.53Ga0.47As–In0.52(Ga1-xAlx)0.48As heterostructures was determinedto be ΔEc(x)=(0.73±0.03)ΔEg(x) (0\leqslantx\leqslant1), by a comparison of the electron (and hole) energy levels in quasi-parabolic (multi-stepped) In0.53Ga0.47As–In0.52(Ga1-xAlx)0.48 As quantum welts observed by photoluminescence excitation spectroscopy, with numerical solutions of Schrodingers equation, where non-parabolicity of the conduction band was considered.

Donor-Related Deep Level in S-Doped Ga0.52In0.48P Grwon by Chloride VPE

A deep level in S-doped Ga0.52In0.48P grown on GaAs by chloride vapor-phase epitaxy was studied by deep-level transient spectroscopy (DLTS). The deep level concentration obtained by DLTS is increased with donor doping intensity as also the case for the obtained by persistent photoconductivity. The energy of this level strongly depends on thermal and optical ionization processes. These properties are the same as those of the DX center. However, the deep level concentration is considerably smaller than that in AlxGa1-xAs(0.3<x<0.7), which makes Ga0.52In0.48P favorable for heterostructure electron devices.

Two-dimensional-electron gas in undoped and selectively-doped GaInP/GaAs heterostructures grown by chloride-vapor-phase epitaxy

This paper reports characteristics of two-dimensional-electron gas (2DEG) in GaInP/GaAs heterostructures and their availability to electronic devices. The heterostructures were fabricated by chloride-vapor-phase epitaxy. The band discontinuity was estimated using an empirical rule. A low-temperature mobility of 2DEG greater than 100,000 cm2/Vs was obtained for the undoped structure. 2DEG was also observed in S or Se selectively-doped structures without incorporating the undoped-spacer layer. Apparent temperature dependence and photoresponse of 2DEG were interpreted with the models which have been used for GaInAs/InP heterostructures.

Quantitative Analysis of In Density in Semi-Insulating GaAs by Photoluminescence

Photoluminescence (PL) measurements at 4.2 K were performed on In-doped semi-insulating GaAs (InxGa1-xAs) grown as a nearly dislocation-free substrate for GaAs large-scale integrated circuits. The In composition x of the sample wafers was calibrated by inductively-coupled-plasma emission spectrometry before the PL measurement. A small variation of In composition in the region 0 ≤x ≤0.0139 was detected by the peak-energy shift of exciton-recombination emissions Δh ν (eV). The value of x could be estimated from Δh ν using the equation x=- Δh ν/1.505 without destruction of the sample wafers. It was found that the emission of neutral-acceptor-bounded-exciton recombination observed in all samples was useful for the measurement of the x value.

Near-Band-Edge Photoluminescenee of High-Purity GaxIn1-xP Grown by Chloride Vapor-Phase Epitaxy

A bound-exciton (BE) emission was studied for high-purity GaxIn1-xP layers grown at various temperatures by chloride VPE. In contrast to the results for the metalorganic-VPE layers, its photon energy did not depend on growth temperature in the range examined (560–760°C). Furthermore, two faint bands were iuavestigated which were observed at photon energies lower than that of BE. They were interpreted from their dependences on temperature and excitation intensity as being due to a donor-acceptor pair emission superimposed by a phonon replica of BE, and to a phonon replica of BE with emission of two phonons.

Electrical Properties of CdCr2Se4. I. p-Type Ag-Doped Single Crystals

Electrical conductivity and Hall effect are measured on p-type Ag-doped CdCr2Se4 single crystals. The carrier concentration has a minimum at temperatures from 140–150 K and then increases as the temperature decreases. This increase in carrier concentration can be interpreted as the onset of conduction in the narrow d band of Cr3+ ions in addition to that in the valence band. The variation of the carrier mobility with temperature can be expressed as µ∝T-S at temperature above 185 K. According to the value of S, the samples are classified into two groups, one with S=1.59 and 1.16, and the other with S=0.25–0.61. It seems that in the former group, the scattering by acoustic phonon is predominant, while in the latter group, the spin-dependent one or the neutral-impurity one is effective, accompanied by phonon scattering.

Performance characteristics of a high‐pressure pulsed singlet oxygen generator

The characteristics of a high‐pressure pulsed singlet oxygen generator is investigated. This generator was designed for the energy source of new pulsed chemical lasers. A ceramic porous pipe is devised in it to attain the high‐pressure pulsed operation. New methods were developed to measure a water vapor pressure and a reaction efficiency in the pulsed singlet oxygen generator system. The maximum singlet oxygen pressure obtained was 35 Torr, and the estimated initial excitation efficiency was 70%–80%

Electrical Properties of CdCr2Se4. II. n-Type In-Doped Single Crystals

Measurements of electrical conductivity and Hall effect have been made on In-doped CdCr2Se4 single crystals from 168 K to 93 K. In the temperature range 168 K to about 140 K, the electron density decreases with an activation energy of 0.23-0.41 eV with decreasing temperature and the mobility increases from 2.1×10-2 cm2/Vs at 168 K to 8.5×10-1 cm2/Vs at 140 K. The electron mobility is so small that the carriers are not considered to move in a broad band in this temperature range. The electron density passes through a minimum at about 140 K and then increases with a further decreases in temperature. The mobility is found to be from 1.2 to 8.5 cm2/Vs below 131 K. It is inferred from the magnitude of the mobility in this temperature range that the conduction occurs in a conduction band, for which a reasonable model is proposed.

Shallow and Deep Donor Levels in S-Doped Ga0.52In0.48P Grown by Chloride VPE

Electrical properties were studied for S-doped Ga0.52In0.48P grown by chloride vapor-phase epitaxy over a wide carrier concentration ranging 1×1015–4×1018 cm-3 using Hall effect measurements. Persistent Photoconductivity caused by the deep level was observed, and was used for an approximate estimation of the deep donor concentration. It was deduced that some of the doped donor atoms form the deep level. The ionization energies of shallow and deep-donor levels were estimated from temperature dependence of carrier concentrations.