Motohisa Hirao

Fabrication and characterization of narrow stripe InGaAsP/InP buried heterostructure lasers

InGaAsP/InP buried‐heterostructure lasers with a stripe width of 1–2 μm have been fabricated by two‐step liquid phase epitaxy and preferential chemical etching. They operate in the fundamental transverse mode at wavelengths of ∼1.3 μm with threshold current as low as 22 mA. The temperature limit for cw operation is 80 °C.

Monolithic integration of a GaAlAs injection laser with a Schottky‐gate field effect transistor

Monolithic integration of a GaAlAs laser with a GaAs Schottky‐gate field effect transistor is demonstrated. A GaAs field effect transistor with a 3‐μm gate length is formed on a double‐heterostructure laser crystal which is protected by a high‐resistivity isolation layer. Laser light intensity is modulated to realize rise and fall times of less than 0.4 ns by modulating the field effect transistor gate voltage.

Monolithic integration of laser diodes, photomonitors, and laser driving and monitoring circuits on a semi-insulating GaAs

A monolithic optoelectronic-integrated circuit (OEIC) incorporating laser diodes, photomonitors, and laser driving and monitoring circuits has been fabricated on a semi-insulating GaAs substrate. The structure and circuit design considerations, the fabrication processes, and the static and dynamic characteristics of the device are described. The device has been successfully operated up to 2 Gbit/s.

Accelerated Aging Characteristics of InGaAsP/InP Buried Heterostructure Lasers Emitting at 1.3 µm

A marked reduction of cw threshold current, to as low as 10 mA at 25°C, was achieved in 1.3 µm InGaAsP InP buried heterostructure lasers with optimized stripe widths of 1.5–2.5 µm, resulting in the feasibility of high temperature operation up to 95°C. For the first time, high temperature cw agings at 50 and 70°C were carried out for lasers in this wavelength region, with successful results.

Low threshold operation of 1.5-µm DFB laser diodes

Highly reliable distributed feedback (DFB) laser diodes operating at 1.5-μm wavelength range are fabricated through optimizing the device parameters. Thickness control of the active layer is found to be an essential factor in achieving low threshold operation of DFB lasers. The threshold current as low as 11 mA and stable single longitudinal mode CW operation up to 106°C is achieved with these DFB lasers.

A Half-Micron Gate GaAs FET Fabricated by Chemical Dry Etching

A new microfabrication method is devised to make a submicron gate GaAs FETs. Ordinary photolithographic techniques are applied to duplicate a one micron pattern on the photoresist film deposited on a thick metal layer. Controlled undercutting of the metal by chemical dry etching produces a submicron contact with the semiconductor, leaving a wide metal top surface. This process gives experimentally confirmed advantages for reproducibility, accurate duplication, easiest lithography and minimal parasitic resistance. Half-micron gate GaAe FETs are fabricated by using this technique combined with triple layer (n«-n-buffer) epitaxial growth. The maximum frequency of oscillation observed is as high as 80 GHz and the noise figure as low as 3 dB at 12 GHz. The new technology has not resulted in any adverse effects and the high frequency performance is improved in direct proportion to the gate length.

Photoluminescence Study of the Interface between GaAs Epitaxial Layer and its Substrate

Photoluminescence measurements are used to study the cause of abnormal interface phenomena, such as non-ohmic behavior or a dip in the carrier concentration profile observed at the interface between a GaAs vapor epitaxial layer and its substrate. From measurements taken on epitaxial crystals grown at different conditions, the emission band which was supposed to be caused by copper impurities are observed at the interface. Therefore these abnormal interface phenomena are probably associated with copper impurities.

Improvement of Crystal Composition in Ga1-xAlxAs LPE Layers Grown under Conditions of Constant Cooling Rate

Liquid phase epitaxy of Ga1-xAlxAs under conditions of a constant cooling rate are analyzed by making use of a diffusion limited growth model. The influence of growth conditions on the AlAs mole fraction in the epitaxial layer as well as the epitaxial layer thickness are investigated in detail. It is shown that the uniform AlAs mole fraction can be obtained by selecting appropriate growth conditions: the cooling rate, solution thickness, and initial supercooling. It is also shown that the dependences of the layer thickness on growth conditions are similar to those of GaAs except for a factor that depends on the AlAs mole fraction.

Reliability of InGaAsP/InP Buried Heterostructure Lasers

Degradation modes of InGaAsP/InP buried heterostructure lasers are classified into three types; rapid, saturable, and gradual degradation. The influences of the temperature dependence of threshold current and the carrier leakage through the buried regions on degradation are described. Lasers that can operate cw above 90°C and show only gradual degradation can be expected to have a mean-time-to-failure of more than 107 h at 25°C.

Switching speed and power dissipation of planar-type Gunn diodes

Abstract The switching speed and power dissipation of planar-type Gunn diodes were investigated both by experiment and theoretical analysis. In the experiment, two-terminal planar-type Gunn diodes with various geometries were fabricated and their switching characteristics were measured under pulse and d.c. biased operations. Under pulse bias, a delay time of 60 psec and a power-delay product of 20 pJ were obtained with Gunn diodes having stick-type active region of 30 μm in length. Under d.c. bias, the geometry of the active region was carefully selected to optimize the trapezoid structure in order to achieve a stable operation, and a delay time of 80 psec and a power-delay product of 50 pJ were obtained. Theoretical analysis showed that the intrinsic delay time of the diodes is 15 psec and that by reducing the parasitic capacitance between the electrodes faster switching will be realized in the experiment.