T. Tanahashi

High‐quality GaN epitaxial layer grown by metalorganic vapor phase epitaxy on (111) MgAl2O4 substrate

We grew GaN crystals by metalorganic vapor phase epitaxy on (111) and (100) MgAl2O4 substrates. We obtained a single‐crystal GaN layer with a specular surface on the (111) substrate. The full width of half‐maximum of the x‐ray rocking curve for a 3.6 μm thick GaN layer was 310 s, comparable to the reported values for GaN on Al2O3 substrates. In the room‐temperature photoluminescence, a band‐edge emission at around 360 nm was dominant. A smooth cleaved (1100) facet of the GaN epitaxial layer was obtained, assisted by the inclined (100) cleavage of the (111) MgAl2O4 substrate. We intend this cleaved facet, which is normal to the surface, to be used as a cavity mirror in a laser diode.

InGaN Laser Diode Grown on 6H–SiC Substrate Using Low-Pressure Metal Organic Vapor Phase Epitaxy

InGaN multiple quantum well (MQW) laser diodes were fabricated on (0001)Si oriented 6H–SiC substrate using low-pressure metal organic vapor phase epitaxy (LP-MOVPE). The laser oscillation was observed above the threshold current of 800 mA at a peak wavelength of 414.3 nm under pulsed current injection at room-temperature. The pulse duration was 300 ns and the repetition frequency was 1 kHz. The threshold current density and differential efficiency were estimated to be 16 kA/cm2 and 0.03 W/A, respectively. The full width at half maximum (FWHM) of the lasing emission lines was between 0.03 nm and 0.21 nm. Streak-shaped far field patterns were clearly observable. The lifetime of the laser diode was more than 5 hours.

CRYSTALLOGRAPHIC ORIENTATION DEPENDENCE OF IMPURITY INCORPORATION INTO III-V COMPOUND SEMICONDUCTORS GROWN BY METALORGANIC VAPOR PHASE EPITAXY

This article presents a comprehensive study of the dependence of impurity incorporation on the crystallographic orientation during metalorganic vapor phase epitaxy of III‐V compound semiconductors. We performed doping experiments for group‐II impurities (Zn and Mg), group‐VI impurities (Se and O), and a group‐IV impurity (Si form SiH4 and Si2H6). The host materials were GaAs, Ga0.5In0.5P, and (Al0.7Ga0.3)0.5In0.5P grown on GaAs substrates. We examined the doping efficiency on the surfaces lying between {100} and {111}A/B. Even though we grew epitaxial layers in a mass‐transport‐limited regime, the doping efficiency significantly depended on the orientation, indicating that the surface kinetics plays an important role in impurity incorporation. Comparing our results with other reports, we found that acceptor impurities residing on the group‐III sublattice and donor impurities residing on the group‐V sublattice, respectively, have their own distinctive orientation dependence. Si donors exhibit orientation d...

Analysis of polarization anisotropy along the c axis in the photoluminescence of wurtzite GaN

The polarization of photoluminescence (PL) was investigated on (1100) GaN grown by metalorganic vapor phase epitaxy. We found that the PL intensity and wavelength have polarization dependence parallel and perpendicular to the c axis. We quantitatively analyzed the dependence and found that, since the crystal field of wurtzite GaN along the c axis is strong enough to fix the |z〉 axis of p functions at the c axis, the difference in symmetry between three valence bands appears as the polarization anisotropy in radiative emission, even in bulk GaN.

Determination of In‐Ga‐As phase diagram at 650 °C and LPE growth of lattice‐matched In0.53Ga0.47As on InP

The liquidus isotherm in the In‐rich corner of the In‐Ga‐As system at 650 °C was experimentally determined by an improved seed dissolution technique using InP seeds. The solidus isotherms at this temperature were also determined in the composition range close to lattice‐matched In0.53Ga0.47As on InP. The solidus data are strongly affected by the crystallographic orientation of the substrate, but are not significantly affected by the degree of lattice matching. The calculated phase diagrams have been compared with the experimental results. The conditions for equilibrium LPE growth of exactly lattice‐matched ternary layers on InP (100) and (111) B substrates were obtained from the results of the phase diagram and lattice‐constant measurements. It was found that the distribution coefficient, growth rate, and surface morphology are strongly dependent on the substrate orientation. The distribution coefficient for Ga and the growth rate at 650 °C are both larger on the (100) face than on the (111) B face. Hillo...

Crystal Orientation Dependence of Impurity Dopant Incorporation in MOVPE-grown III-V Materials

Abstract We investigated the crystal orientation dependence of impurity dopant incorporation in III–V compound semiconductors grown be metalorganic vapor phase epitaxy (MOVPE). Doping experiments were performed for group-II acceptors (Zn and Mg), a group-VI donor (Se), and a group-IV donor (Si from silane or disilane) into MOVPE-grown GaAs, Ga 0.5 In 0.5 P, and (Al 0.7 Ga 0.3 ) 0.5 In 0.5 P. The doping efficiency for each impurity was studied between (100) and (111)A/B faces. Comparing our results to previous reports, we found that there is a general rule in the orientation dependence of impurity incorporation, according to dopant groups. The group-II acceptors (Cd, Mg, and Zn), which reside on the group-III sublattice, are preferentially incorporated on the ( h 11)A face ( h ≥ 1) and, in many cases, incorporated less on the ( h 11)B face ( h ≥ 1) than on the (100) face. I n all materials, the Zn incorporation is most prominent on the (311)A face. In contrast, the group-VI donors, which reside on the group-V sublattice, are preferentially incorporated on the ( h 11)B face ( h ≥ 1) and incorporated less on the ( h 11)A face ( h ≥ 1) th an on the (100) face. Comparing to group-II and group-VI impurities, Si generally exhibits weak dependences. Based on rate limiting processes for the dopant incorporation, we constructed a model for the orientation dependence for the group-II and group-VI impurities, considering atomic bonding geometries between adsorbed impurity atoms and adsorption sites.

OPTICAL GAIN FOR WURTZITE GAN WITH ANISOTROPIC STRAIN IN C PLANE

We calculated band structures of (1100)-oriented GaN with various strains. We found that introducing anisotropic strain in the c plane separates heavy- and light-hole bands. We also found that a tensile strain in the (1100) plane makes the light-hole band topmost. These two effects result in a reduction in the density of states at the valence-band edge. In this way we can significantly reduce the transparent carrier density to generate gain.

V-grooved substrate buried heterostructure InGaAsP/InP laser emitting at 1.3 µm wavelength

Details of the fabrication, optimization of the dimensions of the active region, characteristics, and the aging results of the V - grooved substrate buried heterostructure (VSB) InGaAsP/InP laser are described. It is shown that the VSB laser can be fabricated in one-step epitaxy as well as two-step epitaxy. The active region width below 2.5 μm and the thickness of 0.15-0.2 \mu m are shown to give stable fundamental mode operation and good temperature characteristics. The fundamental mode operation up to the optical output of 20 mW/facet at 25°C and the CW operation above 100°C are obtained. The pulse response showed the strongly damped relaxation oscillation with a frequency as high as 4.5 GHz. The spectral width under the modulation of 400 Mbit/s RZ single is as narrow as 25 A in full width at half maximum. Highly stable aging characteristics at an elevated temperature of 50°C are obtained in both two-step epitaxy lasers and one-step epitaxy lasers.

High‐purity GaSb epitaxial layers grown from Sb‐rich solutions

Undoped GaSb crystals with mirror‐like surfaces were obtained by liquid phase epitaxy from Sb‐rich solutions. The background carrier concentration strongly depended on the growth temperature. By growing crystals below 600 °C, we can obtain a GaSb crystal with a background carrier concentration under 1016 cm−3. Photoluminescence studies showed that native defects related to Sb vacancies were significantly reduced in the GaSb crystal.

Dependence of carbon incorporation on crystallographic orientation during metalorganic vapor phase epitaxy of GaAs and AlGaAs

Abstract We studied the dependence of carbon (C) incorporation on the crystallographic orientation during metalorganic vapor phase epitaxy (MOVPE) of GaAs and AlGaAs. We performed C doping to GaAs grown with trimethylgallium (TMGa) and AsH 3 and Al 0.35 Ga 0.65 As grown with trimethylaluminum (TMAl), TMGa or triethylgallium (TEGa), and AsH 3 on the surface lying between (100) and (111) A/B. C and hole concentrations nearly coincided over the entire orientation range, showing that C is preferentially incorporated at As sites, irrespective of orientation. We found that the dependence of C incorporation on the orientation is more complex than previously thought. The dependence of carrier concentration on the AsH 3 partial pressure reflected the degree of C incorporation very well. Using simultaneous doping with C acceptors and Si donors, we fabricated lateral p-n junctions on patterned substrates composed of the (100) principal surface and (411)A/B sidewalls.