Takashi Ishizuka

Long-Wavelength GaInNAs Vertical-Cavity Surface-Emitting Laser With Buried Tunnel Junction

A long-wavelength GaInNAs vertical-cavity surface-emitting laser with a buried tunnel junction (BTJ) has been demonstrated in this paper. It has been shown that a combination of a GaAs-based BTJ for a current confinement, GaInNAs multi-quantum wells for an active region, a dielectric distributed Bragg reflector (DBR) for a top mirror, and an AlGaAs/GaAs DBR for a bottom mirror is desirable to realize high-speed operation at high temperature. The maximum output power of 4.2 mW with a low resistance of 65 Omega has been obtained at 25degC. Operations of 10 Gb/s have been achieved over the temperature range of 25degC-85degC, with operation current of 6.9 mA and extinction ratio of 5.0 dB.

Direct optical observation of compositional fluctuation in GaAs1-xNx by near-field photoluminescence spectroscopy and microscopy with high spatial resolution

We describe imaging spectroscopy of GaAs1−xNx∕GaAs single quantum wells using low-temperature near-field scanning optical microscope with a high spatial resolution of 35nm. In near-field photoluminescence spectra of a GaAs1−xNx∕GaAs(x=0.7%) quantum well, the narrow spectral peaks with a point emission spatial profile (localized exciton emission) come from local N-rich regions (spontaneous N clusters), and the broad peaks with spatial extension (delocalized exciton emission) are random alloy regions. Localized exciton emissions due to spontaneous N clusters are also observed in GaAs1−xNx with a higher N concentration (x=1.2%).

MOVPE grown InGaAs/GaAsSb type II quantum well photodiode for SWIR focal plane array

Infrared sensors with type II quantum well structure have gained great attention and have shown advanced progress. InGaAs/GaAsSb type II quantum well structures are considered as an attractive material system for realizing low dark current PDs owing to lattice-matching to InP substrate. In this report, we describe successful operation of PIN-PDs with InGaAs/GaAsSb quantum wells grown by metal-organic vapor phase epitaxy (MOVPE). MOVPE method is well-known to have good uniformity which leads to mass-production of focal plane array. Planer type pin-PDs were adopted. The p-n junction was formed in the absorption layer by the selective diffusion of zinc. Electrical and optical characteristics of pin-PDs such as well number dependence of responsivity, were investigated. Dark current was 9.0 μA/cm2 at 233 K, which has better uniformity compared to those of MBE sample, and responsivity of 0.8 A/W in SWIR region were obtained. This result indicates that planer photodiode using MOVPE grown InGaAs/GaAsSb type II quantum wells is a promising candidate for consumer applications.

Fast recovery performance of vertical GaN Schottky barrier diodes on low-dislocation-density GaN substrates

Vertical GaN Schottky barrier diodes (SBDs) were fabricated on free-standing GaN substrates with low dislocation density. Vertical GaN-SBDs with a forward current of 5A and a blocking voltage of 600V exhibit the most superior reverse recovery characteristics among GaN, SiC, and Si diodes. We also confirmed stable forward and reverse aging characteristics for 1000 hours at 150 °C.

High power and low resistive GaInNAs-VCSELs with buried tunnel junctions

GaInNAs-VCSELs with buried tunnel junction structures are proposed and demonstrated. The maximum output powers of 4.2 mW at 25degC and 2.2 mW at 85degC are achieved with a low resistance of 65 Omega.

GaInNAs Distributed Feedback (DFB) Laser Diode

First successful operation of a buried-ridge-type GaInNAs-DFB laser was realized. Under CW condition, it oscillated with a threshold current of 18 mA at 25degC, and it could oscillate up to 110degC with good I-L linearity and with SMSR > 40 dB.

100°C, 10 Gbps operation of buried tunnel junction GaInNAs VCSELs

10 Gbps operation of BTJ GaInNAs VCSELs is achieved over temperature range of 25degC to 100degC with operation current of 5.6 mA and extinction ratio of 4.2 dB.

GaInNAs DFB Laser with Buried GaAs Grating

We for the first time fabricated a GaInNAs DFB laser having a buried GaAs grating in the center current injection region. A successful DFB laser oscillation with the threshold current of 34 mA was obtained

Electroabsorption Effect of GaInNAs in Waveguiding Structure

We investigated the temperature characteristics of the electroabsorption (EA) effect of GaInNAs in a waveguiding structure device. Clear absorption-edge shift by EA effect similar to that at 25 °C was obtained even at a high temperature of 100 °C, and excellent temperature characteristics of EA effect were realized for the case of the six quantum wells (QWs) EA device in which large extinction ratio (ER) values around 20 dB were obtained for the 300-µm-long device, and they were little dependent on temperature between 25 and 100 °C.

GaInNAs Electroabsorption Modulated Laser

We for the first time fabricated an electroabsorption modulated laser (EML) with a GalnNAs multiple quantum well (MQW) active layer using the butt-joint regrowth technique. Single longitudinal mode operation with side-mode suppression ratio (SMSR) of more than 45 dB up to 120degC and the extinction ratio of more than 15 dB up to 100degC were obtained. The 2.5-Gb/s uncooled operation from 25degC to 100degC was successfully demonstrated by changing the EA bias voltage.