Kiyoshi Ohnaka

Improvement of catastrophic optical damage level of AlGaInP visible laser diodes by sulfur treatment

An increase of 70% in the catastrophic optical damage (COD) level of AlGaInP visible laser diodes is achieved by sulfur treatment. From transmission electron microscope and energy dispersive microanalysis, we have confirmed that most of the oxide at the mirror facets is replaced by sulfur after this treatment. It is thought that oxide at the facets introduces surface states which cause the COD, and removal of the oxide by sulfur treatment results in the higher COD level.

Optical Gain Calculation of Wurtzite GaN/AlGaN Quantum Well Laser.

Optical gain properties of wurtzite GaN/Al0.2Ga0.8N quantum well lasers are theoretically analyzed using physical parameters from ab initio calculations for the first time. The valence band of wurtzite GaN exhibits strong non-paraboticity, and the hole density of states is significantly large in comparison with the conventional zincblende crystals. This valence band feature causes high transparency cartier density of 7.5×1018 cm-3 in the 50 A thick GaN quantum well. This result predicts that the threshold current of wurtzite GaN/AlGaN quantum well laser is higher than the conventional lasers with zincblende crystals.

A monolithically integrated InGaAs/InP photoreceiver operating with a single 5-V power supply

A monolithic photoreceiver consisting of an InGaAs p-i-n photodiode and a transimpedance preamplifier in which four junction field-effect transistors four level shift diodes, and a feedback resistor are integrated is described. This photoreceiver has been designed to operate with a single 5-V power supply for the purpose of simplifying the whole transmission system. Easily producible device structures were adopted to increase the yield of the photoreceivers. A circuit transimpedance of 965 Omega and a 3-dB frequency of 240 MHz have been obtained for 5-V operation. Transmission of a 400-Mb/s NRZ signal has been achieved. >

A low dark current InGaAs/InP p-i-n photodiode with covered mesa structure

A new InGaAs p-i-n photodiode with a covered mesa (CM) structure having extremely low dark current characteristics and high yields has been developed. The device consists of only two epitaxial layers: n--InP and n--InGaAs, continuously grown on an n+-InP substrate by liquid-phase epitaxy. The InGaAs layer is chemically etched to be a tapered shape in order to make the fabrication process simple, as compared with a conventional mesa diode. The Zn diffusion to form a p-n junction is carried out without a diffusion mask such as Si3N4or SiO2, which induces damage due to the thermal stress. The tapered-shape InGaAs layer is covered with the Zn-diffused layer because a surface p-n junction occurring in an InGaAs region is leaky. Therefore, the surface p-n junction of the photodiode appears in the n--InP layer, which has a bandgap about two times wider than the InGaAs. Finally, the passivation of the surface p-n junction is carried out with a Si3N4film formed by a plasma-assisted chemical vapor deposition. We have successfully achieved an extremely low dark current of 20 pA at a reverse bias voltage of 10 V and a high yield of 80 percent, by adopting the CM structure and the simple fabrication process.

Analysis of GaInP/AlGaInP compressive strained multiple-quantum-well laser

We have analyzed GaInP/AlGaInP compressive strained MQW lasers, with theoretical calculation and experimental results. Our calculations of TE polarized gain, where the valence subband mixing and the heterobarrier leakage current are taken into account, are in good agreement with the experimental results. When a compressive strain of up to 0.5% is induced in the quantum wells, the density of states near the valence band edge is decreased, due to the reduction of heavy-hole and light-hole subband mixing. At the threshold condition, the compressive strain reduces not only the radiative recombination current, but also the hetero-barrier leakage current. Therefore, the threshold current is reduced, and its temperature dependence is found to be small, In the analysis, we also show that when larger compressive strain of more than 0.5% is induced in the 40-/spl Aring/-thick quantum wells, the threshold characteristics are degraded. >

High power and high‐temperature operation of GaInP/AlGaInP strained multiple quantum well lasers

High power and high‐temperature operation of transverse‐mode stabilized 690 nm AlGaInP strained multiple quantum well lasers is described. Three 0.5% biaxially compressive strained GaInP (8 nm) wells were employed in the active region. Low threshold current of 36 mA and very high output power of 60 mW at high temperature up to 100 °C were obtained with 700 μm long lasers, whose facets were coated with antireflection–reflection films. This is, to the best of our knowledge, the first report that an AlGaInP laser has reached a cw output power of 60 mW at a high temperature of 100 °C. Very low degradation rate at 50 °C with 35 mW output power was confirmed.

A planar InGaAs PIN/JFET fiber-optic detector

A planar structure monolithic optoelectronic integrated circuit (OEIC), comprising an InGaAs PIN photodiode and an InGaAs junction field effect transistor (JFET), has been developed. A cutoff frequency of 1.3 GHz has been successfully obtained. A low dark-current characteristic has also been obtained by polyimide passivation. Design principle, fabrication procedures, and operation characteristics of the PIN/JFET are described.

Extremely high quantum efficiency (86%) operation of AlGaInP visible laser diode with lateral leaky waveguide structure

AlGaInP visible laser diode with lateral leaky waveguide structure has been demonstrated for the first time. The laser has differential quantum efficiency as high as 43% from one facet without coating in addition to stable fundamental transverse‐mode oscillation. The high differential quantum efficiency is due to the propagation loss as low as 4.2 cm−1 of this laser, which is the lowest value for AlGaInP visible diode to the best of our knowledge. This laser can be successfully fabricated by selective growth of AlGaInP quarternary alloy.

Excess gate‐leakage current of InGaAs junction field‐effect transistors

The excess gate‐leakage current of InGaAs junction field‐effect transistors (JFET), which is about 106 times that of the Si JFET, is attributed to hole‐electron‐pair generation produced by impact ionization of the high electric field in the JFET channel. The impact‐ionization rate α is estimated from the excess gate‐leakage current of the InGaAs JFET. At 77 K, the impact‐ionization rate is about one‐half compared with that of 300 K, and the difference between these two temperatures agrees with the calculated polar optical‐phonon scattering rate. The excess gate‐leakage current can be reduced by a factor of 7 by the introduction of a thin n‐InP layer at the interface between the InGaAs channel and semi‐insulating InP substrate.

Theoretical analysis of valence subband structures and optical gain of GaInP/AlGaInP compressive strained-quantum wells

The valence subband structures and optical gain of GaInP/AlGaInP strained quantum wells are theoretically analyzed, using the 4*4 Luttinger-Kohn Hamiltonian. The compressive strain reduces the density of states near the valence band edge. As a result, the differential gain is enhanced for low injection carrier density, and the threshold current is reduced due to the reduction of radiative recombination current. For high injection current, the strain reduces the differential gain, although the threshold current is reduced due to the reduction of the hetero-barrier leakage current.<<ETX>>