C. Wetzel

Determination of piezoelectric fields in strained GaInN quantum wells using the quantum-confined Stark effect

We have identified piezoelectric fields in strained GaInN/GaN quantum well p-i-n structures using the quantum-confined Stark effect. The photoluminescence peak of the quantum wells showed a blueshift with increasing applied reverse voltages. This blueshift is due to the cancellation of the piezoelectric field by the reverse bias field. We determined that the piezoelectric field points from the growth surface to the substrate and its magnitude is 1.2 MV/cm for Ga0.84In0.16N/GaN quantum wells on sapphire substrate. In addition, from the direction of the field, the growth orientation of our nitride epilayers can be determined to be (0001), corresponding to the Ga face.

Reduction of Etch Pit Density in Organometallic Vapor Phase Epitaxy-Grown GaN on Sapphire by Insertion of a Low-Temperature-Deposited Buffer Layer between High-Temperature-Grown GaN

The etch pit density of organometallic vapor phase epitaxy (OMVPE)-grown GaN on sapphire was discovered to reduce drastically by the insertion of either a low-temperature-deposited AlN buffer layer or GaN buffer layer between high-temperature-grown-GaN on sapphire.

Optical band gap in Ga1−xInxN (0<x<0.2) on GaN by photoreflection spectroscopy

The optical band gap in 40 nm Ga1−xInxN/GaN single heterostructures is investigated in the composition range 0<x<0.2 by photoreflection spectroscopy (PR) at room temperature and compared with photoluminescence (PL) data. Clear PR oscillations at the GaInN band gap are observed as originating in the large piezoelectric field. Effective band gap bowing parameters b are derived for pseudomorphically stressed GaInN on GaN: b=2.6 eV (PR) and b=3.2 eV (PL in localized states). Using experimental deformation potentials of GaN, b=3.8 eV is extrapolated for the optical band gap in relaxed GaInN material. Previously reported smaller values are discussed.

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.

Control of Dislocations and Stress in AlGaN on Sapphire Using a Low Temperature Interlayer

In organometallic vapor phase epitaxial growth of AlGaN on sapphire, the role of the low-temperature-deposited interlayers on a high-temperature-grown GaN layer was investigated by in-situ stress measurement, X-ray diffraction, and transmission electron microscopy. Crack-free and low-dislocation-density AlGaN with the whole compositional range has been realized on the sapphire substrate.

Piezoelectric Franz-Keldysh effect in strained GaInN/GaN heterostructures

Pseudomorphic Ga1−xInxN/GaN single heterostructures in the composition range 0<x<0.2 have been investigated by photoreflectance and photoluminescence spectroscopy. Strong Franz–Keldysh oscillations near the band gap of the ternary film are observed and attributed to a large constant piezoelectric field of up to 0.63 MV/cm. This allows an accurate determination of the electric field. A significant redshift between the optical band gap from photoreflectance and the luminescence maximum is observed. Luminescence is proposed to originate in the indirect transitions between the electric field tilted band edges in GaInN. The presence of this field is expected to dominate the bandstructure and the recombination and transport processes in strained nitride structures. We find no evidence for large inhomogeneities or phase separation in this material.

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

GaN Based Laser Diode with Focused Ion Beam Etched Mirrors

GaN-based MQWs-SCH laser diodes (LDs) with Fabry‐Perot resonator mirrors fabricated by focused ion beam (FIB) etching were demonstrated for the first time. The diodes show lasing by pulsed current injection at room temperature with a lasing wavelength near 410 nm. FIB etching of the mirrors significantly reduced the threshold current from 1.25 to 0.75 A. In addition we studied the dependence of I-L characteristics on the successive rotation of the etched mirror of a single device and found a strong angular dependence. A similar study of the tilting angle revealed a very weak variation.