Yoshishige Matsumoto

InGaAsP heterostructure avalanche photodiodes with high avalanche gain

Distinct improvements in avalanche‐gain and dark‐current characteristics have been made in InGaAsP heterostructure APD’s. A planar‐type p‐n junction is formed in an InP window layer, separated from a light‐absorbing InGaAsP layer. This APD structure has yielded an avalanche gain of 3000 and a dark‐current density as low a 1 μA/cm2 at 0.5 Vb.

Low Temperature Growth of GaN and AlN on GaAs Utilizing Metalorganics and Hydrazine

The growth and characterization of AlN and GaN on GaAs are presented. Trimethylgallium (TMG) and trimethylaluminum (TMA) were used as group III sources and hydrazine as a nitrogen source. It was found for both nitrides that mass-transport-limited growth took place at high temperature, and that at low temperature the surface catalyzed decomposition of respective metalorganics manifested itself. Deposition of AlN film was observed at as low as 220°C and that of GaN at 450°C both on GaAs substrates. A distinct proof of cubic-form GaN grown on GaAs is obtained from results of the X-ray precession measurement. The direction of GaN on (100) GaAs, however, is slightly tilted from that of the substrate. It is speculated that this tilt results from the very large lattice-mismatch existing between GaN and GaAs.

Reflection high‐energy electron diffraction and x‐ray photoelectron spectroscopic study on (NH4)2Sx‐treated GaAs (100) surfaces

(NH4)2Sx‐treated GaAs (100) surfaces were heated in an ultrahigh vacuum. Reflection high‐energy electron diffraction (RHEED) and Ga, As, S, and O x‐ray photoelectron spectroscopic (XPS) changes were observed. The sulfide‐treated surface showed a streaky 1×1 RHEED pattern without heating. A 2×1 RHEED pattern appeared during heating to 260 and 420 °C. At these temperatures, the S XPS peak was still observed. The 2×1 pattern is thought to be S induced. On the (NH4)2Sx‐treated surface, no oxidized As XPS signal was observed. Moreover, the O XPS peak disappeared rapidly during the heating above 260 °C. These results suggest that the 2×1 S structure caused the GaAs (100) surface passivation.

Structure Control of GaN Films Grown on (001) GaAs Substrates by GaAs Surface Pretreatments

Two types of cubic and hexagonal GaN films were deposited on (001) GaAs substrates. The film structure proved to be controlled by GaAs pretreatments. By performing a N2H4 (hydrazine) pretreatment of GaAs substrates, the GaN films, which were otherwise hexagonal similarly to ordinary films on sapphire substrates, became cubic. A surface cubic nitride layer was found to be formed on the pretreated GaAs by a RHEED (reflection high-energy electron diffraction) observation, which is thought to be the substantial substrate for the following growth of a cubic GaN film.

Role of Dislocations in Semi-Insulation Mechanism in Undoped LEC GaAs Crystal

For the undoped semi-insulating LEC GaAs crystal, microscopic inhomogeneity was investigated on the fixed position by using cathodoluminescence (CL), secondary ion mass spectrometry (SIMS), X-ray topography (XRT) and scanning leakage current measurement (IL). Microscale fluctuations observed in these measurements were attributed to the cellular dislocation structures. It was suggested that the impurity gettering effect of dislocation plays an important role in the semi-insulation mechanism in GaAs crystal. Carriers are inactive in the boundary region of cell structures but are active in the inner region of cell structures.

Growth Characterization of Low-Temperature MOCVD GaN?Comparison between N2H4 and NH3?

The reaction mechanisms of the low-temperature growth of GaN using TMG (trimethylgallium) and two different nitrogen sources, i.e., N2H4 and NH3, are presented. Quite the same temperature dependence of the growth rate for both N sources was found, suggesting that the transport and decomposition of TMG are growth-rate limiting. A different behavior between the two N sources, on the other hand, is that the flow rate of NH3 that was required to obtain a specular surface of the film was much larger than that of N2H4. This surface specularity could be well described in terms of V/III (input gas molar ratio between N source and TMG) for the case of N2H4, whereas for the NH3 case, V/H2(NH3 partial pressure) was important. A discussion of the detailed growth mechanism, especially the difference in the two N sources, is presented.

Lattice defect structure of degraded InGaAsP‐InP double‐heterostructure lasers

Lattice defect structure of degraded InGaAsP lasers has been investigated by scanning and transmission electron microscopy. It is found that although dislocation climb motion in InGaAsP lasers is slow, slip dislocations parallel to the stripe cause rapid degradation of the lasers.

Unstable horizontal transverse modes and their stabilization with a new stripe structure

Kinks in the light output and other anomalous characteristics in stripe-geometry lasers were studied. It was found that these anomalies were caused by unstable horizontal, parallel to the junction, transverse modes. Introduction of a refractive-index guiding by Zn-diffusion stabilized the horizontal mode and removed the kink and other anomalies completely.

Improvement of the Electrical Properties of the AlN/GaAs MIS System and Their Thermal Stability by GaAs Surface Stoichiometry Control

The GaAs surface pre-treatment conditions for the MOCVD-AlN/GaAs MIS diodes are investigated. An AsH3 pre-treatment just prior to the AlN deposition degraded the C-V characteristics of AlN/n-GaAs MIS diodes in the accumulation side. The characteristics and their stability were drastically improved by a pure H2 pre-treatment at 500°C. It was confirmed that the free As at the interface generates surface states near the conduction band edge and that control of the surface stoichiometry and atomic structure is necessary to improve the MIS characteristics.

Inhomogeneity in Semi-Insulating GaAs Revealed by Scanning Leakage Current Measurements

Inhomogeneity in semi-insulating (SI)-GaAs has been examined by scanning leakage current (IL) measurements. The observed leakage current exhibits broad intensity variation accompanying short period sharp fluctuation along both radial and pulling directions. The undoped SI-GaAs generally shows marked inhomogeneity of the leakage current compared with the Cr-doped GaAs. The broad IL intensity variation along the radial direction is correlated with dislocation distribution. Thermal annealing at 850°C for 1 hour in H2 significantly smooths out the inhomogeneity.