Noboru Hamao

Double heterostructure optoelectronic switch as a dynamic memory with low‐power consumption

A pnn double heterostructure optoelectronic switch with dual extractor electrodes was dynamically operated as an optical memory with the resulting achievement of 20 μW holding power. This value represents a reduction in holding power of about three orders of magnitude as compared to that of conventional light‐emitting optical bistable devices. Complete operation, involving optical writing, regeneration, and high‐speed erasing of written data through a dual extractor‐electrodes configuration, was carried out with a simple driving scheme.

Vertical to surface transmission electrophotonic device with selectable output light channels

A photoeletronic bistable device with selectable light output channels has been fabricated for implementation in photonic switching and processing systems. The device is a variation of the vertical to surface transmission electrophotonic device. Output in the stimulated light emission mode was successfully obtained from different waveguide channels by external electronic switching. Output channels could be switched at a rate of 400 Mb/s. The potential versatility of this device has been experimentally confirmed in programmable or switchable optical interconnections.

High Speed Response in Optoelectronic Gated Thyristor

High speed response in a three terminal pnpn double heterostructure optoelectronic gated thyristor is demonstrated. The gate electrode on the active layer is operated to sweep out excess carriers in the active layer. The turn-off delay time has been measured to be 5 ns, which is two orders of magnitude improvement compared with that for the two terminal mode operation. Furthermore, it has been shown that the turn-off delay time cannot be estimated from the conventional 90-10% fall time.

Reduction in interfacial recombination velocity by superlattice buffer layers in GaAs/AlGaAs quantum well structures

The values of interfacial recombination velocities in GaAs/AlGaAs double heterostructures and quantum wells grown by molecular beam epitaxy with and without superlattice cladding layers are obtained with photoluminescence time‐decay measurements. The authors show that superlattice layers reduce the interfacial recombination velocity from 330 cm/s, the value for double heterostructures with alloy cladding layers, to 40 cm/s, and that they have small effect on the GaAs bulk lifetime.

Chlorine-Based Smooth Reactive Ion Beam Etching of Indium-Containing III-V Compound Semiconductor

Very smooth and vertical etching of InP by Cl2 reactive ion beam etching has been achieved under high temperature (≈200°C), high ion energy (≈1 keV) and low Cl2 pressure (~10-5 Torr). The roughness is estimated to be a few nm by scanning tunneling microscopy and no contamination except for Cl was observed by in situ Auger electron spectroscopy. Under these etching conditions, the etched depth is precisely controlled (σ=22 nm) by simply monitoring the electrode curtent of the ion accelerating grid. Other III-V compound semiconductors, such as GaAs, InGaAs, AlGaInP and InAlAs have also been etched smoothly and vertically. Multilayers of these materials, such as InP/InGaAsP, AlGaInP/GaInP, and InAlAs/InGaAs/InP have been etched without steps between the layers on the sidewalls.

High‐speed all‐optical switching experiment in Mach–Zehnder configuration using GaAs waveguide

We report the results of a high‐speed all‐optical switching experiment in Mach–Zehnder configuration using a GaAs waveguide. The all‐optical switching is based on the nonlinear refractive index change induced by the band‐filling effect in the GaAs waveguide. To achieve high‐speed operation without being limited by the slow carrier relaxation time, a dc electric field is externally applied to the nonlinear waveguide to sweep carriers away from the light guiding region. The FWHM (full width at half maximum) of the switching waveform without the externally applied electric field is about 800–900 ps. As the electric field is increased, the FWHM is reduced to about 80–90 ps.

Smooth and vertical InP reactive ion beam etching with Cl2 ECR plasma

Smooth and vertical InP reactive ion beam etching has been achieved with electron cyclotron resonance Cl2 plasma at high ion energy (≥900 eV), high temperature (230°C) and relatively low Cl2 pressure (~10-4 Torr). Smooth etching of an InP system by Cl2 plasma has often been reported as difficult compared to that of the GaAs system due to low volatility of reactive products such as InClx. In the present work, precise control of incident ion energy and Cl2 pressure contributed to the improvement of both the vertical profile and bottom smooth surface under high substrate temperature (~200°C). Vertical profiles were easily achieved even at high temperatures by varying the Cl2 pressure. While etching conditions suitable for vertical wall-formation were maintained, surface morphology was drastically improved by increasing ion energy above 900 eV and the bottom roughness became less than 100 nm at 1450 eV.

Surface‐emitting GaAs/AlGaAs lasers with dry‐etched 45° total reflection mirrors

Surface‐emitting GaAs/AlGaAs lasers with 45° total reflection mirrors have been successfully produced using a 45° tilted reactive ion beam etching technique. The ratio of surface‐emitted light output power to edge‐emitted light output power was obtained at values as high as 77%. The total reflection mirror was formed within 1° of the desired precise 45° angle. This type of surface‐emitting laser is promising for optoelectronic integrated circuits because of the simplicity of its structure and fabrication.

Switching Experiments with a Mach-Zehnder-type All-Optical Device Based on the Band-Filling Nonlinearity in a GaAs Waveguide and Reduction in Its Relaxation Time

We examine switching characteristics of an all-optical device in Mach-Zehnder configuration, that is based on the band-filling nonlinearity in a GaAs waveguide. Switching waveforms corresponding to π (full switching), 2π, and 2.7π have been obtained and they were compared with theoretical curves. Good agreement has been observed between experimental and theoretical results. The control light pulse energy required for full switching is estimated to be approximately 6 pJ. The switching speed of the above device is limited by the slow relaxation time of photogenerated carriers. In order to reduce the switch-off time determined by the carrier relaxation, we investigated a method which involves application of a DC electric field across the thin core layer of the waveguide in order to sweep photogenerated carriers away from the light-guiding region and effectively reduce the relaxation time. With this technique, the usual switching speed of approximately 1 ns was reduced to approximately 24 ps.

Reduction in sidewall recombination velocity by selective disordering in GaAs/AlGaAs quantum well mesa structures

Sidewall recombination in SiO2‐capped GaAs/AlGaAs multiple quantum well mesa structures is investigated using a time‐resolved photoluminescence technique. Nonradiative recombination lifetimes in annealed samples are improved significantly compared with those in samples which are not annealed. This effect contributes to a reduction in sidewall recombination velocity due to disordering of quantum wells at the sidewall by cap annealing. Numerical analysis is used to fit the experimentally observed sample size dependence of the nonradiative lifetimes to calculated curves. This shows that the effective sidewall recombination velocity is reduced from 8×106 to 4×104 cm/s.