Takao Kajiwara

ZnSe‐ZnS strained‐layer superlattice grown by low pressure metalorganic vapor phase epitaxy using methylalkyls

Good quality ZnSe‐ZnS strained‐layer superlattice (SLS) has been successfully fabricated for the first time by low pressure metalorganic vapor phase epitaxy (MOVPE) using methylalkyls (dimethylzinc, dimethylselenide, and dimethylsulfide). The satellite peak observed by x‐ray diffraction measurements and the periodic behavior of the atomic profiles by secondary ion mass spectrometry measurements confirm the formation of the SLS structure. From the photoluminescence measurements, the quantum size effect has been evidenced by the relationship between the ZnSe well‐layer thickness and the peak energy shift of the light emission. Our results show that low pressure MOVPE using VI group alkyls can be quite useful for the growth of ZnSe‐ZnS SLS.

Operation principle of the InGaAsP/InP laser transistor

A laser transistor functions both as a semiconductor laser and a heterojunction bipolar transistor. It generates stimulated emission light from the base region. We have obtained, typically, a maximum laser power of 3 mW, a current gain of 2000, and a transition frequency of 2.5 GHz for the fabricated devices. We show that the novel light output control can be obtained by changing its collector voltage. Both laser output and collector current can also be simultaneously controlled by changing the base current.

Low-loss short-wavelength optical waveguides using ZnSe-ZnS strained-layer superlattices

Low‐loss short‐wavelength optical ridge waveguides using ZnSe‐ZnS strained‐layer superlattices (SLS’s) were successfully fabricated on GaAs substrates by low‐pressure metalorganic vapor phase epitaxy. A propagation loss α as low as 0.71 cm−1 was obtained for the SLS waveguide composed of 80 periods of ZnSe(50 A)‐ZnS(50 A) at the 0.633‐μm wavelength TE fundamental mode. Therefore, this waveguide may be suited for optoelectronic integrated circuits composed of II‐VI and III‐V compound semiconductor devices. Furthermore, these waveguides exhibited a large difference in the propagation loss between TE and TM polarizations which may be related to the birefringence for TE and TM polarizations due to the slight anisotropy of the refractive index in the ZnSe‐ZnS superlattice structure. This birefringence effect will be very useful for a polarizing optical device.

High quality ZnSe films grown by low pressure metalorganic vapor phase epitaxy using methylalkyls

High quality ZnSe layers have been successfully grown by low pressure metalorganic vapor phase epitaxy (MOVPE) using methylalkyls, dimethylzinc, and dimethylselenide. Streaks and Kikuchi lines were observed by reflective high‐energy electron diffraction measurements. Also the sharp and strong excitonic emission line due to free exciton and no emissions related to deep levels or residual impurities were observed by photoluminescence measurements. These results show that the ZnSe layers are of good crystalline quality. Furthermore, good selective growth of the ZnSe films on structured substrates was easily achieved by using this low pressure MOVPE technique.

Effect of device parameters on bistable semiconductor laser

The effect of device parameters on static and dynamic properties of inhomogeneously current‐injected bistable semiconductor lasers has been analyzed. It is shown that in addition to the fraction of current injection region in the cavity, the device parameters, such as dopant concentration in active layer, facet reflectivity, and cavity length, affect the hysteresis width and threshold current. The mechanism of transition between lasing and nonlasing states is discussed, in which a new interpretation is given about the bias dependence of switch‐on delay time and the driving condition for switching off is clarified. The carrier increasing rates due to the bias current and dopant concentration in the active layer are dominant factors for the switching on and switching off, respectively.

Analysis of optical polarization bistability in transverse‐magnetic‐wave‐injected semiconductor lasers

Optical polarization bistability induced by transverse‐magnetic‐ (TM) wave injection is thought from experimental results to originate from simultaneous generation of the oscillation of the transverse‐electric wave (TE oscillation) and the amplification of the transverse‐magnetic wave (TM amplification). In order to prove authenticity of this assertion, we use rate equations that include a term of the TM mode and an equation of the transmittance of the laser cavity. The calculations show that the carrier density is kept constant in the low‐TM‐photon‐density region while it varies in the high‐TM‐photon‐density region. It is also shown that the constant gain is divided into both TM amplification and TE oscillation in the former region. The transmittance changes only in the latter region since the refractive index varies with the carrier density. The bistability appears between these two regions. Calculated light output versus light input characteristics show good agreement with the experimental results.

ZnSe/ZnS heteroepitaxial growth using an intermediate strained‐layer superlattice buffer

High‐quality ZnSe layers have been successfully grown on ZnS layers with an intermediate ZnSe‐ZnS strained‐layer superlattice (SLS) by low‐pressure metalorganic vapor‐phase epitaxy. If we use the SLS buffer between the ZnSe and ZnS layer, the excitonic‐emission line in the photoluminescence spectra of the ZnSe epilayers due to the free exciton becomes stronger and emissions related to misfit dislocations weaker compared with those of the ZnSe layer grown directly on the ZnS layer. Reflective high‐energy electron diffraction measurements also showed that these (100) ZnSe layers grown on the SLS buffer were single crystals. With double‐crystal x‐ray diffraction, it is supposed that the misfit strain was completely relaxed by using the SLS buffer in only 0.6‐μm‐thick ZnSe layer grown on the ZnS layer. From these results, we have found that the ZnSe‐ZnS superlattice buffer is very useful for obtaining a good ZnSe/ZnS heterostructure.

Optical polarization bistability with high switching speed in a TM wave injected buried heterostructure laser

We demonstrate optical polarization bistability in a semiconductor laser for the first time. Only the optical signal pulses are used as triggers for switching the transverse mode of the laser. The two stable states are identified as the transverse electric mode and the transverse magnetic mode, respectively, while the optical input consists of the transverse magnetic wave. Switching speeds up to a few hundred picoseconds have been achieved for both switch‐up and switch‐down.

LPE growth and characterization of InGaAsP/InP multiquantum well epitaxial layers

Abstract This paper presents very thin InGaAsP/InP layers grown by the LPE-sliding growth technique and the characterization of the fabricated multiquantum well (MQW) layers. In the LPE growth mechanism of the very thin layer, the transient region having a thickness of 60 to 75 A is formed at the onset of the growth under nonequilibrium conditions of the solid-liquid interface, while a very thin layer is grown under diffusion-limited conditions. For MQW layers, the degeneration split between the heavy- and light-hole levels has been recognized from the photoluminescence measurements, and ±1st and ±2nd order satellite peaks of the superlattice have been observed in the rocking curves of the double X-ray diffraction. Furthermore, it has been recognized that the lattice constant of the very thin layers in the LPE-grown InGaAsP/InP MQW layers was shifted to that of the InP layers by the relaxation of the strain at the heterointerfaces.

Fabrication and lasing characteristics of 1.3‐μm InGaAsP multiquantum‐well lasers

This paper reports the fabrication and lasing characteristics of 1.3‐μm InGaAsP multiquantum‐well (MQW) buried heterostructure (BH) lasers grown by liquid‐phase epitaxy (LPE) technique. The MQW active region consists of five InGaAsP well layers (λg=1.3‐μm, Lz∼200 A and InGaAsP barrier layers (λg=1.1 μm, d∼400–600 A). These lasers have threshold currents of 15–20 mA at 25 °C, external quantum efficiencies of 50% at 25 °C, and T0 values of 130–145 °K in the temperature range of less than 300 °K. The beam divergences perpendicular and parallel to the junction plane were in the narrow range of 10–13°. Furthermore, the polarization‐dependent gain‐current relationship between the TE and TM mode of InGaAsP MQW lasers has been investigated in detail for the first time.