Shigekazu Minagawa

Ordered structure in OMVPE-grown Ga0.5In0.5P

Abstract The ordered structure of Ga and In in GaInP grown on (001) GaAs by organometallic vapor phase epitaxy (OMVPE) is investigated using high-resolution transmission electron microscopy (TEM). Cross-sectional TEM reveals that the main structure consists of ( 1 2 1 2 1 2 ) and ( 1 2 1 2 1 2 orderings. These orderings are sequences of (111) planes arranged in the order of Ga/P/In/P/ Ga/P/In/P along the [111] and [11 1 ] directions, respectively. The ordered structure may be thermodynamically stable. The OMVPE growth mechanism may partly determine ordering direction in the crystal.

Influence of growth temperature on crystalline structure in Ga0.5In0.5P grown by organometallic vapor phase epitaxy

The relation between growth temperature and ordered structures in Ga0.5In0.5P grown using organometallic vapor phase expitaxy is investigated using transmission electron diffraction, electroreflectance, and Raman scattering measurements. It is found that generation of the ordered structure is not related to the immiscibility of this alloy and that the ordered structures do not simply represent ‘‘sublattice ordering.’’ The anomalous band gap may be a consequence of the variation in the atomic arrangement of neighboring atoms, but not of the long‐range ordered structure itself.

Anomalous temperature dependence of the ordered Ga0.5In0.5P photoluminescence spectrum

The temperature dependence of the photoluminescence spectrum of Ga0.5 In0.5 P/GaAs grown by organometallic vapor phase epitaxy is measured. Samples with a highly long‐range ordered structure show anomalous behavior, where peak energy changes with temperature exhibiting Z‐shape dependence. In the range between 100 and 30 K, peak energy decreases monotonously with decreasing temperature, and below 30 K, begins to increase, splitting into two peaks. The most probable cause of this behavior is crystal defects related to the long‐range ordered structure.

Selective growth of gallium nitride layers with a rectangular cross‐sectional shape and stimulated emission from the optical waveguides observed by photopumping

Selective growth of GaN layers on sapphire substrates is investigated for low‐loss optical waveguide structures of active and passive photonic devices. When growth conditions, such as nitridation of the substrate surface and growth temperature, are adjusted to achieve high‐density uniform nucleation on the substrate, we found that the cross‐sectional shape of GaN waveguides has a rectangular structure with smooth top and side surfaces. At 77 K, we observed stimulated emission from the cleaved facet of an optically pumped selectively grown GaN waveguide with a width of 6 μm and a cavity length of 800 μm. Line narrowing was also achieved: with the full width at half‐maximum of the emission spectra decreasing from 11 to 2 nm by increasing a pump power density from 0.013 to 0.05 MW/cm2.

Etching of GaN Using Phosphoric Acid

Hot phosphoric acid is found to be useful for etching and characterizing epitaxial crystals grown on (0001) sapphire substrates. The obtained etch rates are 0.2–1.0 μm/min and the activation energy is about 4.4 kcal/mole in the temperature region of 50°–200°C. Hydration of Ga ion is considered the rate‐determining step of the etching action. The x‐ray diffraction and the infrared spectrometric studies indicate that the ortho and meta phosphoric ions play an important role as attacking ions in etching. This phosphoric acid etching reveals crystal defects in undoped (n), Zn‐doped (i), and i‐n structure epitaxial crystals. Conical hexagonal pyramid pits and truncated hexagonal pits develop in the undoped layers, and they tend to be arranged along the slip direction and are attributed to certain dislocations. These hexagonal pits are densely generated near the interface of the epitaxial layer and the substrate. The density of the pits decreases exponentially with crystal growth. The pits are apt to increase in density and size when the carrier concentration is high (1019–1020 cm3). The rounded etch figures develop in Zn‐doped crystals and sometimes in the undoped crystals with a high carrier concentration (1019 cm−3). Etching also indicates that there is a significant difference in growth patterns between the Zn‐doped and the undoped crystals even if the Zn‐doped layer is continuously deposited on the undoped layer. This implies a difference in the crystal growth mechanism between these crystals.

Kinetics of the epitaxial growth of GaN using Ga, HCl and NH3

Abstract This paper deals with the effects of the growth parameters, the position of the substrate, the reactant gas flow rate and the substrate temperature, upon the epitaxial growth rate of GaN on (0001) sapphire substrates. The growth technique used was the chemical vapor deposition method utilizing Ga, HCl and NH3. The crystal growth rate in the presence of excess NH3 increases linearly with the quantity of Ga transported from the source zone, whereas it decreases exponentially with the distance from the inlet nozzle end. The activation energy for the GaN formation is estimated to be about 1.1 eV (25 kcal/mol), and this energy is interpreted as that for the surface reaction step. These results are discussed from a simple chemical kinetics standpoint.

Study on photoluminescence and Raman scattering of GaInP and AlInP grown by organometallic vapor‐phase epitaxy

The photoluminescence and Raman scattering spectra of GaInP and AlInP grown by organometallic vapor‐phase epitaxy are measured to investigate the ordered and disordered crystalline states. It is found that ordered structure exists not only in the GaInP but also in the AlInP, and probably in the entire AlGaInP system, and that zinc doping over 1018 cm−3 makes it disordered. This disordering effect is attributed to the Zn diffusion in the GaInP epilayer during crystal growth which puts the once‐formed ordered atomic arrangement into a disordered state.

Raman scattering from AlGaInP

Raman scattering spectra from AlGaInP quaternary alloys grown on GaAs substrates are measured. Dominant peaks observed are identified as AlP‐, GaP‐, and InP‐like longitudinal optical modes. Mode frequency is seen to change almost linearly with aluminum composition, exhibiting the ‘‘partly three‐mode type’’ behavior.

OMVPE growth of gallium indium phosphide on the {100} gallium arsenide using adduct compounds

Epitaxial layers of gallium indium phosphide were grown on the {100} surfaces of gallium arsenide using an OMVPE (organometallic vapor phase epitaxial) growth technique which utilizes adduct compounds composed of trimethyl metals and triethylphosphine. The influence of growth conditions on such properties of the grown layers as surface morphology, crystal defects, composition, photoluminescence spectra and carrier concentration was investigated. Lattice-matched epitaxial layers with featureless surfaces were obtained and examination with photoluminescence and SIMS techniques showed their composition was very uniform. For example, the deviation in photoluminescence peak position across a 15 mm × 15 mm wafer at room temperature was found to be less than ±0.5 nm. The carrier concentration of the undoped layers was 2 × 1015 cm−3 at the lowest with most of them in the low end of the 1016 cm−3 range. The half-width of the photoluminescence peak was as narrow as 48 MeV at room temperature and 19 meV at 77 K. The growth rate was 1.5–3 μm/h.

Polycrystalline Indium Phosphide Solar Cells Fabricated on Molybdenum Substrates

Heterojunctions on polycrystalline indium phosphide films are fatbricated and characterized. The InP films are chemically deposited on molybdenum substrates. Cuprous selenide films, being cubic in crystal structure and degenerate in conduction, are prepared on n-type InP films. CuxSe/InP thin film solar cells have efficiencies of up to 1.7% with a short circuit current density of 11 mA/cm2 under AM 1 simulated irradiation. Furthermore, CdS/InP heterojunction solar cells are fabricated by evaporating indium-doped CdS films on zinc-doped InP surfaces. The efficiency directly increases with the annealing temperature of the cells up to 2.0% with a short-circuit current density of 18 mA/cm2. A collection efficiency of 70% is obtained at a wavelength of 0.65 µm from a spectral response curve. In addition, the electron diffusion length is calculated to be 0.2 µm, which determines the lower collection efficiency at longer wavelengths.