Tsukuru Katsuyama

Effects of strained-layer structures on the threshold current density of AlGaInP/GaInP visible lasers

We have investigated the effects of strained‐layer structures on the reduction of the threshold current density of AlGaInP/GaInP visible laser diodes. It was found that a remarkable reduction of the threshold current density could be realized by incorporating strained single quantum well structures in their active regions. The minimum threshold current density at room temperature under pulsed conditions is 215 A/cm2, which is by far the lowest value ever reported for AlGaInP/GaInP visible lasers and comparable to those of AlGaAs/GaAs lasers.

High temperature (≳150 °C) and low threshold current operation of AlGaInP/GaxIn1−xP strained multiple quantum well visible laser diodes

High temperature and very low threshold current operation of a separate confinement heterostructure (SCH) AlGaInP/GaxIn1−xP (x=0.43) strained multiple quantum well (SMQW) lasers has been achieved. Continuous wave (cw) operation was observed up to at least 150 °C with an output power of more than 7 mW, which is the highest cw operating temperature ever reported for devices operating in the visible wavelength region. The characteristic temperature between 20 and 80 °C was 130 K. The threshold current and threshold current density at 25 °C were 13.9 mA for a 5×160 μm device and 430 A/cm2 for a 80×770 μm device.

Metalorganic Vapor Phase Epitaxial Growth of GaNAs Using Tertiarybutylarsine (TBA) and Dimethylhydrazine (DMHy).

GaNAs alloys were successfully grown on GaAs substrates by low-pressure metalorganic vapor phase epitaxy (MOVPE) with all organometallic sources of triethylgallium (TEG), tertiarybutylarsine (TBA), and dimethylhydrazine (DMHy). For nitrogen, the desorption coefficient of 30 kcal/mol was derived from the nitrogen incorporation dependence on growth temperature. Since the nitrogen concentration above 3% was easily achieved by our growth technique, the combination of TBA-DMHy as V precursors is a candidate for the growth of other III-V alloys containing nitrogen. We observed a decrease in PL intensity with enhancing nitrogen incorporation into solids. In order to recover from degradation of optical properties, rapid thermal annealing (RTA) was demonstrated and found to be effective. Therefore MOVPE using TBA-DMHy combined with postgrowth annealing is expected to obtain GaNAs alloys with high nitrogen concentration as well as excellent optical properties.

Novel Vertical Heterojunction Field-Effect Transistors with Re-grown AlGaN/GaN Two-Dimensional Electron Gas Channels on GaN Substrates

Novel vertical heterojunction field-effect transistors (VHFETs) with re-grown AlGaN/GaN two-dimensional electron gas (2DEG) channels on free-standing GaN substrates have been developed. The VHFETs exhibited a specific on-resistance (RonA) of 7.6 mΩ cm2 at a threshold voltage (VTH) of -1.1 V and a breakdown voltage (VB) of 672 V. The breakdown voltage and the figure of merit (VB2/RonA) are the highest among those of the GaN-based vertical transistors ever reported. It was demonstrated that the threshold voltage can be controlled by the thickness of AlGaN layers and a normally-off operation was achieved with a 10-nm-thick Al0.2Ga0.8N layer.

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.

1.3 µm Traveling-Wave GaInNAs Semiconductor Optical Amplifier

We fabricated a GaInNAs semiconductor optical amplifier (SOA) by applying a facet coating to a buried-ridge-stripe GaInNAs laser. Due to a low reflectivity (<0.1%) and a wide bandwidth (70 nm) coating, Fabry–Perot (FP) modes of the GaInNAs laser were suppressed sufficiently, and thus a 1.3 µm traveling-wave GaInNAs SOA was realized for the first time. Peak chip gains of more than 9.6 dB and a 3-dB-gain bandwidth above 49 nm (9 THz) were obtained simultaneously with a cavity length between 600 µm and 900 µm. In addition, on/off ratios between 20 and 30 dB were obtained by switching the current on and off, which seems sufficient for the SOA to work as a switching device. With the temperature characteristics, we found that the ASE intensity and the gain coefficient of the GaInNAs SOA were much less dependent on temperature than those of conventional InP-based SOAs. These results demonstrate the superior temperature characteristics of the GaInNAs SOA compared with conventional InP-based SOAs.

Eight-channel wavelength multiplexing with 200-GHz spacing using uncooled coaxial fiber Bragg grating external-cavity semiconductor laser module

As a low-cost light source for wavelength-division-multiplexing networks, the authors develop an uncooled coaxial fiber Bragg grating external-cavity semiconductor laser (FGL). To realize high-wavelength stability, an FGL structure is adopted, and to reduce the cost of light source itself, a coaxial pigtail module structure is selected. High-wavelength stabilities of 2 pm/mA and 12 pm/K against current and ambient temperature variation are realized. Using the FGLs, successive eight-channel wavelength multiplexing with 200-GHz spacing and with almost the same peak power is realized between -30/spl deg/C to 70/spl deg/C. For each channel, the wavelength difference from the corresponding ITU grid is only within /spl plusmn/0.1 nm at 25/spl deg/C.

Aging time dependence of catastrophic optical damage (COD) failure of a 0.98-/spl mu/m GaInAs-GaInP strained quantum-well laser

In this paper, we studied the aging time dependence of the catastrophic optical damage (COD) failure of an Al-free uncoated 0.98-/spl mu/m GaInAs-GaInP strained quantum-well laser with an injection current as a parameter. Based on the stress-strength model, we first investigated experimentally the dependence of the critical power level (CPL) at which COD would take place upon the aging time. Then applying a statistical treatment to this result, we found for the first time that CPL data at each aging time could be considered to distribute according to the Weibull statistics, and the decrease rate of the CPL with the aging time depended very strongly on the injection current. Finally, using the relationship between the decrease rate of the CPL with the aging time and the current, we predicted roughly the time of a COD failure occurrence for both large and small current cases. As a result, we clarified that for our Al-free uncoated 0.98-/spl mu/m laser, a COD failure became a fatal problem in the case of a large-current (high-power) operation.

Surface Treatment by Ar Plasma Irradiation in Electron Cyclotron Resonance Chemical Vapor Deposition

To reduce the surface states of GaAs and related semiconductors which originate from native oxides on a surface, we developed a simple surface treatment method in which the surface oxides could be physically sputtered by Ar plasma irradiation in an electron cyclotron resonance chemical vapor deposition (ECR-CVD) apparatus. In the experiment of Ar irradiation of a GaAs surface, we were able to determine the optimum irradiation time at which the native-oxide-related surface states were almost removed without damaging the irradiated surface. Then, we applied this method to an actual 0.98-µm semiconductor laser in which catastrophic optical damage (COD) failure occurred due to the surface states of the output facet. By irradiating Ar plasma to the output facet of the laser and removing the oxide-related surface states there, tolerance to COD was remarkably improved compared with that of a conventional non-Ar-irradiated one.

Interdiffusion of GaAs/Ga1-xInxAs quantum wells

We report results of an investigation of interdiffusion in GaAs/Ga0.82In0.18As strained single quantum wells. Wells of width 12–100 A, grown by organometallic vapor phase epitaxy, were subjected to 10 s rapid thermal anneals of 830–950 °C, and shifts in the electron‐to‐heavy‐hole transition energies were detected by 4 K photoluminescence. We employed a powerful computer model to relate postdiffusion well shape to changes in photoluminescence energies, enabling estimation of diffusivity. Interdiffusion rates of 1×10−16–2×10−14 cm2/s and activation energies of 3.1–3.8 eV were obtained.