Seiichi Miyazawa

Model for molecular‐beam‐epitaxy growth over nonplanar surfaces

A model for molecular‐beam‐epitaxy growth is proposed to describe the morphology formed on a nonplanar, profiled surface that may consist of multifaceted crystal structures. Anisotropy of growth rate is introduced as a main factor for explaining the observed growth morphology. We show that on the nonplanar surface, the migration of adatoms modifies the growth rate at each point of the growing surface and thus affects the formation of the morphology within the range of migration length. The model can successfully describe the growth behavior including the development of sharp facet edges, since it is formulated in terms of a difference (rather than differential) equation which does not require the continuity of surface slope. The morphology simulated on the basis of this model agrees to experimental results of GaAs growth.

Competing processes of Si molecular beam reactive etching and simultaneous deposition on film and bulk SiO2

The Si molecular beam reactive etching of thick thermally grown SiO2 and bulk SiO2 has been studied. In situ observations by Auger electron spectroscopy and reflection high energy electron diffraction reveal that Si films grow epitaxially on Si (100) substrates at 1000 °C after removal of 0.5 μm thermally grown SiO2 by a Si molecular beam. It is found that simultaneous deposition of polycrystalline Si films containing many oxygen atoms occurs on etched SiO2 at 900 °C. Surface morphology of the etched bulk SiO2 and the Si over layers caused by simultaneous deposition is observed by scanning electron microscopy.

Low-Temperature Molecular Beam Epitaxy Growth of Single Quantum Well GaAs/AlGaAs Lasers

We report on the low-temperature Molecular Beam Epitaxy (MBE) growth of single quantum well (SQW) GaAs/AlGaAs lasers under a low flux ratio. Lasing action was observed at a substrate temperature as low as 300°C. A threshold current density of 600 A/cm2 was obtained at the substrate temperature of 375°C, which is the lowest threshold current density below 400°C reported so far.

Threshold Current Density of GaAs/AlGaAs Single-Quantum-Well Lasers Grown by Molecular Beam Epitaxy

We report on the effect of substrate temperature on the threshold current density in GaAs/AlGaAs single-quantum-well lasers grown by molecular beam epitaxy under various flux ratios. It is found that the threshold current density has W-shape dependence on the substrate temperature and exhibits minima of 600 A/cm2 and 400 A/cm2 at the substrate temperatures of 375°C and 650°C, respectively.

Photoluminescence from GaAs/AlGaAs Quantum Wells Grown at 350°C by Conventional Molecular Beam Epitaxy

Photoluminescence measurements have been carried out for GaAs/AlGaAs single quantum well (SQW) structures grown without interruption by conventional molecular beam epitaxy. The full widths at half-maximum (FWHM) from QWs having thin well width were reduced monotonously with the decrease of growth temperature until 350°C to one-half. This reduction of FWHM was explained by the transition of the top and bottom heterointerfaces which became close to the effective smooth interfaces at 350°C. The peak intensity had only a weak dependence on the growth temperature at the same temperature.

Continuous wave operation on extremely low‐temperature (375 °C)‐grown AlGaAs quantum‐well lasers

We report on the continuous wave (cw) operation of AlGaAs single‐quantum‐well (SQW) lasers grown at a low temperature (375 °C) by molecular‐beam epitaxy (MBE). The threshold current and the differential quantum efficiency of the ridge‐waveguide laser were 10 mA and 82%, respectively. During the life test, no obvious degradation was observed beyond 2300 h under 8 mW cw operation at 50 °C. The cw operation of SQW lasers grown at low temperatures was achieved by the long baking of the MBE system and the reduction of the V/III flux ratio.

A Study On Laser Scanning Systems Using A Monolithic Arrayed Laser Diode

It is well known that a monolithic arrayed laser diode is effective for a high-speed laser beam printer. In terms of the angular relation between the arrayed direction and the laser beam scanning line, two typical laser scanning optical systems using a monolithic arrayed laser diode are comparatively discussed in this paper. As for the first optical system, the arrayed direction is slightly tilted from the scanning lines direction. While this system has an advantage of easiness in the data processing technique in comparison with the other optical system, we have to pay attention in designing and manufacturing this optical system in terms of accuracy and complicateness. The second optical system forms a striking contrast to the first. The lasers arrayed direction of the second optical system is perpendicular to the laser beam scanning line. In this system, we need no such particular designing nor manufacturing as in the first one described above, but interlacing scanning method and the relevant data processing technique. Through comparing the above two systems, we are discussing optical issues. As the conclusion, we think, the second system of interlacing method would become popular in consideration of the future advances in data processing technique.

Polarization switching in a tensile-strained InGaAs/InGaAsP multiple quantum well distributed feedback laser diode

An inhomogeneously biased distributed feedback (DFB) laser diode (LD) with two electrodes switched its polarization mode by 3 mA change of the bias current, maintaining single longitudinal mode oscillation. In the active layer of the LD, 13 nm thick and 0.6% tensile-strained InGaAs multiple quantum well (MQW) equalized the transverse electric and the transverse magnetic modal optical gain at 1.55 μm. With various grating pitches on the same MQW active layer, polarization switching DFB LDs were realized in the wavelength range as wide as 18 nm. The linewidth characteristics during the polarization switching were confirmed to be narrow due to the small switching current.

High‐reliability GaAs/AlGaAs multiquantum well lasers grown at a low temperature (375 °C)

We report on high‐reliability GaAs/AlGaAs multiquantum well (MQW) lasers grown at a low temperature (375 °C) by molecular beam epitaxy (MBE). Typically, a threshold current (Ith) of 26 mA and a differential quantum efficiency of 62% were obtained during a continuous wave (cw) operation at room temperature. During the life test, a stable operation was observed beyond 5000 h under a 20‐mW cw operation at 70 °C. We also observed an improvement of laser characteristics in low‐temperature‐grown MQW lasers during a cw operation at room temperature. The threshold current of our MQW lasers was reduced from 26 to 18 mA, and this suggests that the point defects in the low‐temperature‐grown MQW laser were decreased.