Michihiko Kariya

STRUCTURAL PROPERTIES OF INN ON GAN GROWN BY METALORGANIC VAPOR-PHASE EPITAXY

InN has been expected to be a suitable material for electronic devices such as high mobility transistors because of its small effective mass compared to other nitrides. Heteroepitaxial InN films were grown by metalorganic vapor-phase epitaxy. The films have been structurally characterized by triple-axis x-ray diffraction (XRD) analysis in terms of lattice-mismatch dependence and InN film thickness dependence, and Hall measurements have been performed. In the XRD measurement, ω and ω–2θ scans were used, and the degree of tilting (the linewidth of x-ray signal, Δωc) [(0002) reflection] and that of twisting (Δωa) [(1010) reflection] have been separated. In addition, the degree of distribution of lattice constant c (Δ2θc) [(0002) reflection] of InN films has been assessed. For study of the lattice-mismatch dependence, growth of InN films on GaN, AlN and directly on sapphire substrates was performed, and accordingly, Δωc was found to range from about 500 to 4000 arcsec, and Δ2θc from about 400 to 700 arcsec. ...

Anomalous features in the optical properties of Al1−xInxN on GaN grown by metal organic vapor phase epitaxy

We have studied the optical properties of Al1−xInxN thin films grown on GaN by metal organic vapor phase epitaxy. X-ray diffraction analysis of ω and ω-2θ scans showed that both the compositional fluctuation and the degree of crystalline mosaicity increase with increasing x. While the energy positions of both the absorption edge and photoluminescence peak shift to a lower-energy region with increasing x, the linewidth of the photoluminescence spectra and the value of the absorption edge tail decrease. The Stokes shift also decreases with increasing x, following which both energy positions become 1.66 eV, which is smaller than the band gap of InN (1.9 eV). These anomalous features of the optical properties of Al1−xInxN might be affected by the absorption in the infrared region caused by the high electron concentration.

Structural and optical properties of AlInN and AlGaInN on GaN grown by metalorganic vapor phase epitaxy

We studied structural and optical properties of Al 1~x In x N and Al 1~y~z Ga z In y N films. The films were grown on GaN by atmospheric pressure metalorganic vapor-phase epitaxy. GaN was grown on a c-plane sapphire substrate with a low-temperature-deposited AlN bu⁄er layer. Photoluminescence (PL), absorption and X-ray di⁄raction measurements of Al 1~x In x N showed that PL and absorption spectral peaks shift to lower photon energy with increasing alloy composition x and that Al 0.83 In 0.17 N has the highest crystallinity. ( 1998 Elsevier Science B.V. All rights reserved.

Strain relief and its effect on the properties of GaN using isoelectronic In doping grown by metalorganic vapor phase epitaxy

We studied the effect of isoelectronic In doping on the crystalline and optical properties of GaN grown on sapphire with H2 or N2 carrier gas by metalorganic vapor phase epitaxy. The relationship between lattice constants c and a obtained by x-ray diffraction analysis showed that with increasing trimethylindium (TMI) flow during growth, the strain in GaN decreased, and accordingly, the tilting and the twisting components of crystalline mosaicity also decreased. In addition, the Raman shift, the excitonic photoluminescence peak energy, and the its linewidth shifted in accordance with the magnitude and the sign of the strain in GaN, regardless of the carrier gas used. These results revealed that for a smaller TMI flow region, In was incorporated so that the crystallinity of GaN improved, and for a larger TMI flow region, In substituted for Ga so that alloying formation might have occurred.

Mass transport and the reduction of threading dislocation in GaN

This is the first report of the observation of mass transport of single crystalline GaN. A wafer with the squared grooves was annealed at 1100°C under flows of NH3 and N2. During the annealing, no group-III alkyl source gas was supplied. After 12 min annealing, all the stripes were buried due to a mass transport of GaN from the unetched region. The mechanism of mass transport is discussed. The strong crystallographic anisotropy of GaN is expected to modulate the shape of the mass transported region. Transmission electron microscopy revealed that threading dislocations were bent and did not climb through the mass transported region. Therefore, a dislocation-free region was achieved at the upper part of the mass transported region except for one dislocation observed at the center of the groove. This method is promising for the fabrication of dislocation-free GaN on sapphire substrate.

Structural Properties of Al 1- xIn xN Ternary Alloys on GaN Grown by Metalorganic Vapor Phase Epitaxy

Michihiko KARIYA, Shugo NITTA, Shigeo YAMAGUCHI, Hisaki KATO, Tetsuya TAKEUCHI,Christian WETZEL, Hiroshi AMANO andIsamu AKASAKIDepartment ofElectrical and Electronic Engineering, Meijo University, 1-501Sl1iogamagucl1i, Tempaku-ku.Nagoya 468-8502.Japan(Received April 23, 1998; accepted for publication May 7,1998)Ah_xlnxN layers grown on GaN by metalorganic vapor phase epitaxy (MOVPE) have been structurally studied usingwand

Observation of photoluminescence from Al1−xInxN heteroepitaxial films grown by metalorganic vapor phase epitaxy

We have observed photoluminescence of Al1−xInxN films. The films were grown on GaN by atmospheric pressure metalorganic vapor phase epitaxy. GaN was grown on a c-plane sapphire substrate with a low-temperature deposited AlN buffer layer. Photoluminescence, absorption, and x-ray diffraction measurements have shown that each spectral peak shifts with alloy composition x and that Al1−xInxN heteroepitaxial films are not macroscopically in phase separation and are constituted in the wurzite structure.

Mosaic Structure of Ternary Al 1-xInxN Films on GaN Grown by Metalorganic Vapor Phase Epitaxy

Al1-xInxN heteroepitaxial films were grown on GaN by atmospheric pressure metalorganic vapor phase epitaxy. The films were characterized by X-ray diffraction and atomic force microscopy. In the case of Al0.50In0.50N, the crystallinity progressively degraded with increasing thickness. On the contrary, the crystallinity of Al0.83In0.17N, which is in-plane lattice-matched with GaN, remained almost unchanged irrespective of the thickness. The crystallinity of Al0.83In0.17N was strongly dependent on the quality of the underlying GaN layer, while that of Al0.50In0.50N was not as sensitive.

Control of strain in GaN by a combination of H2 and N2 carrier gases

We study the effect of a combination of N2 and H2 carrier gases on the residual strain and crystalline properties of GaN, and we propose its application to the improvement of crystalline quality of GaN/Al0.17Ga0.83N multiple quantum well (MQW) structures. GaN was grown with H2 or N2 carrier gas (H2– or N2–GaN) on an AlN low-temperature-deposited buffer layer. A (0001) sapphire substrate was used. N2–GaN was grown on H2–GaN. The total thickness was set to be 1.5 μm, and the ratio of N2–GaN thickness to the total thickness, x, ranged from 0 to 1. With increasing x, the tensile stress in GaN increased. Photoluminescence intensity at room temperature was much enhanced. Moreover, the crystalline quality of GaN/Al0.17Ga0.83N MQW was much higher when the MQW was grown with N2 on H2–GaN than when it was grown with H2 on H2–GaN. These results were due to the achievement of control of strain in GaN using a combination of N2–GaN and H2–GaN.

Strain relief by In-doping and its effect on the surface and on the interface structures in (Al)GaN on sapphire grown by metalorganic vapor-phase epitaxy

We have performed a growth technique that involves isoelectronic In-doping into GaN and AlGaN in order to reduce defects. The films were grown by atmospheric metalorganic vapor-phase epitaxy (MOVPE) at 950°C in a H2 or N2 carrier gas (denoted below by H2-(Al)GaN and N2-(Al)GaN, respectively) with a low-temperature-deposited AlN buffer layer. By using this technique, we were able to control the strain in the films; with increasing trimethylindium (TMIn) flow, the strain in GaN was decreased; accordingly, the tilting and twisting components of crystalline mosaicity (tilt and twist, respectively) were also decreased. The Raman shift and photoluminescence (PL) emission peak energy were shifted in accordance with the strain in GaN. The PL linewidth decreased with the decrease in the strain in GaN. Strong enhancement of the excitonic PL intensity of In-doped GaN and AlGaN was observed. The surface morphology was also dramatically improved on In-doping, and the growth pits on the films were distinguished. These results are not due to the surfactant effect of In because we confirmed from the secondary-ion mass spectroscopy (SIMS) results that In was incorporated in the films. The above results could be explained by considering the solid-solution hardening effect.