Yasuo Nannichi

A GaAs-AlxGa1-xAs Double Heterostructure Planar Stripe Laser

A stripe laser structure called a planar stripe was developed. The edge blurring of the current path is improved by the fact that the current spreads only in the thin p-AlxGa1-xAs layer with relatively high resistance. The planar stripe laser has a small threshold current resulting from the small current spreading effect and a good thermal contact. It also shows finely controlled transverse modes, compared with a usual contact stripe laser, and relatively high external differential quantum efficiency. The threshold current density is comparable to that of the proton bombarded stripe laser. The transverse mode shows an approximate Hermite-Gaussian distribution.

Universal Passivation Effect of (NH4)2Sx Treatment on the Surface of III-V Compound Semiconductors

The effectiveness of (NH4)2Sx treatment on the (100) surface of GaP, (Al, Ga)As, InP and InAs was studied in comparison to that on GaAs by means of Auger electron spectroscopy (AES) and reflection high-energy electron diffraction (RHEED). It was concluded that the existence of sulfur atoms bonded to semiconductors prevents the adsorption of oxygen. This phenomenon brings about the metal-dependent Schottky barrier fabricated on the (NH4)2Sx-treated surfaces, implying the reduction in the interface state density. The structure and effect of the (NH4)2Sx-treated surface of III-V compounds are qualitatively the same.

The Effect of (NH4)2S Treatment on the Interface Characteristics of GaAs MIS Structures

MIS capacitors prepared on the (NH4)2S-treated GaAs substrate showed a marked reduction in the density of the dominant pinning levels near 0.6 eV below the conduction band. The annealing effect on the interface characteristics was also investigated. Analyses by means of secondary ion mass spectroscopy (SIMS) and Auger electron spectroscopy (AES) indicate that sulfur atoms at the interface stabilize the oxygen-free GaAs surface both electronically and thermally.

Synchrotron radiation photoemission analysis for (NH4)2Sx-treated GaAs

The chemistry of the (NH4)2Sx‐treated n‐GaAs (100) surfaces has been studied using synchrotron radiation photoemission spectroscopy. Ga 3d, As 3d, and S 2p photoemission spectra are measured before and after annealing in vacuum with a photon energy of about 210 eV, where S 2p core level spectra can be sensitively detected. It is found that Ga‐S, As‐S, and S‐S bonds are formed on the as‐treated GaAs surfaces, and that stable Ga‐S bonds become dominant after annealing at 360 °C for 10 min in vacuum. The thickness of the surface sulfide layer is reduced from about 0.5 to 0.3 nm by annealing. The surface Fermi‐ level position of the as‐treated surfaces is determined to be about 0.8 eV below the conduction band minimum, which is about 0.1 eV closer to the valence band maximum than that of the untreated surfaces. A Fermi‐level shift of 0.3 eV toward a flat band condition is also observed after annealing. It is found that the Ga‐S bonding plays an important role in passivating GaAs surfaces.

Metal-Dependent Schottky Barrier Height with the (NH4)2Sx-Treated GaAs

Schottky barriers have been prepared on (NH4)2Sx-treated GaAs. The barrier height was observed to change remarkably with the kind of metals, which is predicted in the case of low interface state density. We found that the interface trap density was reduced to 9.8×1012 cm-2eV-1 by the treatment from 6.5×1013 cm-2eV-1 for the untreated one.

Studies on an (NH4)2Sx-Treated GaAs Surface Using AES, LEELS and RHEED

Surface properties of (NH4)2Sx-treated GaAs (100), (111)Ga and ()As planes were studied by means of Auger electron spectroscopy (AES), low-energy electron energy loss spectroscopy (LEELS) and reflection high-energy electron diffraction (RHEED). We found that oxide-free and sulfur-terminated GaAs surfaces produced by the (NH4)2Sx treatment provided the reduction of interface state density. Furthermore, comparison of various planes revealed that (i) sulfur atoms could combine with both Ga and As and (ii) bonding between Ga and S was stronger than that between As and S.

Plasma CVD of Amorphous AlN from Metalorganic Al Source and Properties of the Deposited Films

AlN films have been successfully deposited by plasma CVD for the first time. Al was supplied by trimethyl Al (TMA) with H2 or N2 carrier gas, and N was supplied as NH3 through separate gas lines. The deposition rate depends upon the TMA supply, and is essentially independent of the NH3 flow rate. The composition of the deposited films was almost AlN, although a small amount of oxygen was always detected. A better film was obtained for the H2 carrier gas than for N2 carrier gas. X-ray diffraction profiles of the deposited films exhibited no crystalline AlN diffracting peaks, suggesting that the films are not crystallized, but the infrared and ultraviolet absorption spectra exhibited the presence of the Al–N bond (650/cm) and an optical band gap of 5.55 eV. The refractive index was about 1.9. These results suggest that the plasma-deposited films possess dominant AlN properties even though they are not crystalline.

Effects of Be and Si on disordering of the AlAs/GaAs superlattice

Effects of Be doping and the interaction of Be and Si on the disordering of 15‐nm AlAs/15‐nm GaAs superlattices were studied. Be doping of more than 4×1019 cm−3 causes the intermixing of Al and Ga during epitaxial growth and the effect of Be surface accumulation is observed at the growth temperature of 540 °C, while after incorporation of Be in the crystal the annealing of 750 °C, 2 h does not cause any remarkable change in the superlattice structure. Be doping in the Si‐doped superlattice shows remarkable suppression of the disordering of superlattice when the Be doping level exceeds that of Si.

Disordering of Si-Doped AlAs/GaAs Superlattice by Annealing

Effect of Si-doping levels and annealing temperature on disordering of 150-A AlAs/150-A GaAs superlattices is studied. The doping level of 4×1018 cm-3 cause disorder for 800°C, 2 h annealing, while the doping level of 1×1018 cm-3 does not induce disorder on this annealing condition. A superlattice which is doped with 1×1019 Si cm-3 disintegrates after 650°C, 2 h annealing and the diffusion coefficient of Al–Ga interdiffusion is estimated to be 3×10-17 cm2s-1. For 800°C, 2 h annealing the two undoped AlAs/GaAs layers adjacent to the doped region are disordered by Si diffusion.

Marked Reduction of the Surface/Interface States of GaAs by (NH4)2Sx Treatment

MIS capacitors have been fabricated on (NH4)2Sx-treated GaAs using a SiOx insulator prepared by conventional resistive-heating evaporation. The MIS interface state density was found to be about 1.2×1011 cm-2·eV-1 in a wide range of the band gap, which is two orders of magnitude less than that on the as-etched GaAs.