Masatomo Fujimoto

Effect of hot-electron injection of high-frequency characteristics of abrupt In/sub 0.52/(Ga/sub 1-x/Al/sub x/)/sub 0.48/As/InGaAs HBT's

The effect of hot-electron injection energy (E/sub i/) into the base on the high-frequency characteristics of In/sub 0/52/(Ga/sub 1-x/Al/sub x/)/sub 0.48/As/InGaAs abrupt heterojunction bipolar transistors (HBTs) is investigated by changing the composition of the emitter. There exists an optimum E/sub i/ at which a maximum current gain cutoff frequency (ft) is obtained. Analysis of hot-electron transport in the base and collector by Monte Carlo simulation is carried out to understand the above phenomenon. The collector transit time ( tau /sub c/) increases with E/sub i/, because electrons with higher energy transfer from the Gamma valley into the upper L and X valleys. At first, the base transit time ( tau /sub b/) decreases with E/sub i/ at the low E/sub i/ region. However, tau /sub b/ does not decrease monotically with E/sub i/, because of the nonparabolicity in the energy-band structure of InGaAs. Consequently, there exists a minimum in the sum of tau /sub b/ and tau /sub c/, in other words a maximum f/sub t/, at an intermediate value of E/sub i/. >

Low-Temperature Si Surface Cleaning by Hydrogen Beam with Electron-Cyclotron-Resonance Plasma Excitation

Si surface cleaning is successfully carried out at as low as 400°C using hydrogen ECR plasma. SIMS analysis reveals no detectable accumulation of either carbon or oxygen at the grown-layer/Si interface. Hydrogen plasma cleaning is found equally effective for unbiased and positively biased Si substrates. On the other hand, helium plasma is not as effective as hydrogen plasma for cleaning. These results imply that the major mechanism involved in the plasma cleaning is chemical reaction between silicon oxide and chemically active hydrogen radicals, rather than physical bombardment by hydrogen ions.

A Rutherford Backscattering Spectroscopic Study of the Aluminum Antimonide Oxidation Process in Air

The oxidation process of aluminum antimonide (AlSb) in air is investigated in detail using Rutherford backscattering spectroscopy (RBS). It is verified that AlSb is extremely liable to be oxidized by slight exposure to air. The oxidation is found to be a two-step process: an initial fast step and a subsequent slower one. In the initial step, a surface oxide with a thickness of about 150 A is formed after AlSb is exposed to air for only a matter of minutes. This oxide gradually thickens in the subsequent step, reaching the AlSb/GaSb interface after exposure for about eighty hours. It is also clarified that the oxidized AlSb layer is amorphous and that a partly oxidized region is formed under the amorphous oxidized AlSb layer in a precursory state.

Observation of deep levels in undoped GaSb grown by molecular beam epitaxy

Deep levels in undoped GaSb grown by molecular beam epitaxy are investigated with the deep level transient spectroscopy method. The measurements are performed on diodes consisting of undoped and Te‐doped GaSb layers. Three hole traps are detected in the undoped GaSb, the activation energies of shallowest and deepest traps being 0.25 and 0.63 eV, respectively. The depth profile of trap concentration suggests that the origin of these two traps is related to native defects or interdiffusion of Te from n+ layer. The capture cross sections of these traps are also measured by using the filling pulse technique.

Surface currents in InP/InGaAs heterojunction bipolar transistors produced by passivation film formation

The correlation between the passivation film formation for InP/InGaAs heterojunction bipolar transistors and transistor current-voltage (I-V) characteristics is investigated. The I-V characteristics vary significantly depending on the kind of passivation films. The major change in I-V characteristics is the increase in base current (Ib),which implies the generation of an additional recombination process around the surface of the emitter-base junction. A change in collector current (Ic) is also observed, indicating that the electron injection mechanism changed near the passivated semiconductor surface. These surface currents are produced by the interaction of the semiconductor surface with the passivation films. It is shown that these surface currents are greatly suppressed using a buffered hydrofluoric acid solution before the passivation film formation.

1.5 µm InGaAsP/InP BH Lasers on p-Type InP Substrates

The 1.5 µm InGaAsP/InP lasers on p-type InP substrates have been realized by a simple fabrication process. By utilizing buried-heterostructure, a low threshold current of 40 mA under cw operation and a large operating current range, 1 A, were achieved

New Methods of Vapour Phase Epitaxial Growth of GaAs

New vapour growth methods using the Ga–AsCl3–H2 and GaAs–AsCl3–H2 systems are proposed. In these methods, the apparatus is basically the same as the conventional Ga–AsCl3–H2 system, but the source and the substrate are kept at the same temperature. The growth in the Ga–AsCl3–H2 system is based on the reaction between gallium monochloride and arsenic that is being passed over metallic gallium at low temperatures (<800°C). The influences of the temperature, the hydrogen flow rate, and the gas composition on the growth rate are studied. The growth in the GaAs–AsCl3–H2 system is based on the reaction of GaAs with AsCl3 at low temperatures (<700°C). The transport rate of the source GaAs and the growth rate of epitaxial layers are discussed as functions of the reaction temperature, the hydrogen flow rate, the gas composition and the position of substrate. The reaction mechanisms for the two systems are also discussed.

Suppression of AlSb oxidation with hydrocarbon passivation layer induced by MeV‐He+ irradiation

A very thin hydrocarbon coating layer of at most a few monolayers induced by the electronic scattering of MeV‐He+ ion‐beam irradiation effectively and completely suppresses oxidation of the compound semiconductor AlSb, which is liable to be oxidized by mere exposure to air, because of the coating layer’s hydrophobic property. Of the many kinds of hydrocarbons, alkyl and phenyl groups are particularly effective for oxidation suppression. The AlSb oxidation mechanism and oxidation suppression mechanism are discussed.

Surface Cleaning of AlGaAs Substrates by Hydrogen Electron Cyclotron Resonance (ECR) Plasma

Surface cleaning of AlGaAs substrates by hydrogen electron cyclotron resonance (ECR) plasma is carried out. Plasma is transported to the substrate surface by a divergent magnetic field. In situ reflection high-energy electron diffraction (RHEED) observation reveals that surface cleaning of AlGaAs can be successfully performed at a temperature as low as 500°C. From secondary ion mass spectrometry (SIMS) measurements, oxygen concentrations at the interface between the AlGaAs substrate and the GaAs layer grown after plasma cleaning are found to decrease as the substrate temperature decreases. At 500°C, flat surfaces with streaked RHEED patterns and clean interfaces with neither carbon nor oxygen accumulations can be obtained by hydrogen ECR plasma cleaning.

Direct Growth of AlGaAs/GaAs Single Quantum Wells on GaAs Substrates Cleaned by Electron Cyclotron Resonance (ECR) Hydrogen Plasma

Direct growth of AlGaAs/GaAs single quantum wells (SQWs) on GaAs substrates without growing buffer layers is carried out by using electron cyclotron resonance (ECR) hydrogen plasma cleaning. SQW structures are successively grown by molecular beam expitaxy (MBE) after the cleaning process without breaking the vacuum. Photoluminescence shows intense and narrow spectra, in clear contrast to that of conventional thermal cleaning. Atomic force microscopy (AFM) and secondary ion mass spectroscopy (SIMS) analyses show that surface roughness and interface impurity accumulations are significantly reduced as well. A flat and clean surface obtained by plasma cleaning improves the quality of grown layers.