Yoshiji Horikoshi

Low-Temperature Growth of GaAs and AlAs-GaAs Quantum-Well Layers by Modified Molecular Beam Epitaxy

When Ga or Al atoms are evaporated on a clean GaAs surface in an As-free atmosphere, they are quite mobile and migrate very rapidly along the surface even at low temperatures. This characteristic are utilized for growing high-quality GaAs and AlAs layers at very low temperatures by alternately supplying Ga or Al atoms and As4 molecules to the GaAs substrate. Applying this method, GaAs layers and AlAs–GaAs quantum well structures with reasonable photoluminescence characteristics are grown at 200°C and 300°C, respectively.

Migration-enhanced epitaxy of GaAs and AlGaAs

Surface migration is effectively enhanced by evaporating Ga or Al atoms onto a clean GaAs surface under an As-free or low As pressure atmosphere. This characteristic was utilized by alternately supplying Ga and/or Al and AS4 to the substrate surface for growing atomically-flat GaAs-AlGaAs heterointerfaces, and also for growing high-quality GaAs and AlGaAs layers at very low substrate temperatures. The migration characteristics of surface adatoms have been investigated through reflection high-energy electron diffraction measurements. It was found that different growth mechanisms are operative in this method at both high and low temperatures. Both these mechanisms are expected to yield flat heterojunction interfaces. By applying this method, GaAs layers and GaAs-AlGaAs single quantum-well structures with excellent photoluminescence were grown at substrate temperatures of 200 and 300degC, respectively.

Abrupt p‐type doping profile of carbon atomic layer doped GaAs grown by flow‐rate modulation epitaxy

Atomic layer doping of p‐type carbon impurity in GaAs was demonstrated using flow‐rate modulation epitaxy. An extremely narrow capacitance‐voltage profile with 5.8 nm full width at half‐maximum is observed in the wafer with a sheet hole density of 9.5×1011 cm−2. Atomic layer doping of carbon was performed by supplying trimethylgallium or trimethylaluminium instead of triethylgallium. It was found that the sheet hole density does not change before and after annealing for 1 h at 800 °C indicating that the carbon is a very stable impurity in GaAs. The diffusion coefficient of carbon is estimated to be 2×10−16 cm−2/s at 800 °C. This is the lowest value ever reported for p‐type impurities.

Temperature Sensitive Threshold Current of InGaAsP–InP Double Heterostructure Lasers

The threshold current of InGaAsP–InP double hetetostructure lasers has been investigated through measurements of the temperature dependence of carrier lifetime and radiative efficiency. Both the carrier lifetime and the radiative efficiency decrease noticeably above the break point temperature as observed in the Ith vs. T relation. The decrease of the carrier lifetime is explained by considering additional non-radiative recombination centers with 0.3 eV activation energy. The origin of this center is also discussed.

Growth process of III–V compound semiconductors by migration-enhanced epitaxy

Abstract The growth mechanism of GaAs and AlGaAs in migration-enhanced epitaxy is investigated by RHEED observation and optical scattering measurements. The available Ga site density on a (2 × 4) reconstructed GaAs (001) surface is much less than the ideal density due to a missing As-dimer array structure. The layer-by-layer growth of GaAs by migration-enhanced epitaxy proceeds by repeated formation and annihilation of small Ga droplets. The growth process is also investigated by studying growth on singular and vicinal (001) GaAs planes. The observed step-flow growth is explained by considering the different chemical characteristics of the steps along the [110] and [ 1 10] directions. The results are compared with those of other growth methods such as molecular beam epitaxy and metalorganic vapor phase epitaxy.

Effect of Well Size Fluctuation on Photoluminescence Spectrum of AlAs–GaAs Superlattices

Photoluminescence spectra for undoped superlattices exhibited smaller half widths compared with those obtained in GaAs bulk crystals. However, both the spectral width and shape were found to be very sensitive to the well size. When the well size is greater than about 80 A, the spectrum at 77 K showed smaller linewidth, which agrees with theoretical results, whereas when the well size is smaller than this, the spectral width increased with decreasing well size. In some cases, additional emission bands appeared in the lower energy side of the main emission peak. These phenomena were interpreted in terms of well size fluctuations.

Atomic configuration of the Er‐O luminescence center in Er‐doped GaAs with oxygen codoping

This article investigates the structure of an Er luminescence center in GaAs by using its intra‐4f‐shell luminescence spectrum as an atomic probe to identify the atomic configuration. This Er center is formed in GaAs by metalorganic chemical vapor deposition with O codoping and the center shows a high efficiency and a sharp luminescence spectrum under above‐band‐gap photoexcitation. A single luminescence line in the spectrum of a GaAs:Er,O splits into more than eight lines in the spectrum of Al0.01Ga0.99As:Er,O. This drastic change due to the addition of 1% Al can be explained by assuming that, because of the high tendency of Al atoms to react with O atoms, the Al atoms preferentially occupy the nearest‐neighbor Ga sites of two O atoms, both of which are coupled with the Er atom. Based on the luminescence spectra and additional experiments of Rutherford backscattering and secondary ion mass spectroscopy, we propose that the structure of the Er luminescence center under study is Er occupying the Ga sublatt...

Optical Investigation on the Growth Process of GaAs during Migration-Enhanced Epitaxy

The growth process of GaAs is investigated using optical reflection during migration-enhanced epitaxy which is based on an alternate deposition of Ga atoms and As4 molecules onto the growing surface. A linearly polarized laser light is irradiated at a 20° angle with respect to the (001)-oriented GaAs substrate surface. A 325-nm He-Cd laser light with polarization E vector perpendicular to the substrate surface is more efficiently reflected from Ga-stabilized surfaces than from As-stabilized surfaces. Thus, strong and persistent oscillation in reflection intensity is observed during the alternate deposition of Ga and As4. When the polarization E vector of the incident light is parallel to the growing surface, no oscillation is observed. These results imply that the observed optical reflection oscillation is related to the optical absorptions caused by an electronic transition in the As-stabilized surface which couples efficiently with light whose polarization vector is normal to the surface.

FLOW-RATE MODULATION EPITAXY OF GaAs.

We propose a flow-rate modulation epitaxy method which yields high-purity GaAs layers with improved growth rate controllability. This method is based on an alternate gas flow of triethyl gallium (TEG) and arsine (AsH3) by using hydrogen carrier gas. The most characteristic point of this method is that a very small amount of AsH3 is added during the TEG flow period. This small amount of AsH3 suppresses the formation of arsenic vacancies near the growing surface, and thus reduces the incorporation of impurity atoms. As a result, we could obtain high purity GaAs layer at relatively low growth temperatures.

Intrinsic Defects in ZnO Films Grown by Molecular Beam Epitaxy

We have investigated the intrinsic defects in ZnO films grown by molecular beam epitaxy by annealing them in O2 and N2 atmosphere. We found that there is a good correlation between the annealing condition and photoluminescence characteristics. The results of annealing experiments suggest that the photoluminescence at 3.358 eV is caused by the excitons bound to oxygen vacancies. The green-yellow emission at around 2.3 eV is also observed in as-grown ZnO epitaxitial films. This emission becomes weak and the electron concentration increases when ZnO films are annealed in O2 atmosphere at 1000°C or in N2 atmosphere at 700°C. Since the donor in undoped ZnO is related to the oxygen vacancy, the observed green-yellow emission at around 2.3 eV is probably caused by defects other than oxygen vacancies. Our experimental results imply that it is related to interstitial Zn.