Masaaki Nido

Room-Temperature Continuous-Wave Operation of InGaN Multi-Quantum-Well Laser Diodes Grown on an n-GaN Substrate with a Backside n-Contact

Continuous-wave operation at room-temperature has been demonstrated for InGaN multi-quantum-well (MQW) laser diodes (LDs) grown on low-dislocation-density n-GaN substrates with a backside n-contact. The current, current density and voltage at the lasing threshold were 144 mA, 10.9 kA/cm2 and 10.5 V, respectively, for a 3 µm wide ridge-geometry diode with high-reflection dielectric coated mirrors. Single-transverse-mode emission was observed in the far-field pattern of the LDs and the beam full width at half power in the parallel and perpendicular directions was 6° and 25°, respectively.

High-quality InGaN MQW on low-dislocation-density GaN substrate grown by hydride vapor-phase epitaxy

Abstract A low-dislocation-density thick GaN layer was successfully grown using selective-area HVPE growth combined with epitaxial lateral overgrowth. The InGaN MQWs fabricated on this thick GaN layer showed superior optical properties compared with that on a sapphire substrate. Mg diffusion, induced by threading dislocations, was greatly suppressed for the LEDs on the HVPE-grown GaN layer. The results clearly indicate that the HVPE-grown GaN substrate will be useful for achieving high-performance light-emitting devices.

Novel Ridge-Type InGaN Multiple-Quantum-Well Laser Diodes Fabricated by Selective Area Re-Growth on n-GaN Substrates

A novel ridge structure fabricated by selective-area epitaxial re-growth is proposed for InGaN multiple-quantum-well (MQW) laser diodes (LDs). This technique is capable of precisely controlling the active ridge width and height, thus enabling stable single tran sverse-mode operation. Together with a backside n-contact on a low-dislocation-density GaN substrate, this structure provides high productivity and performance for GaN-based blue-violet LDs. A stable fundamental transverse mode up to 40 mW was demonstrated for the certain range of ridge dimensions. The minimum aspect ratio of the far-field patterns (FFPs) was about 2.1 in the fabricated ridge-type InGaN MQW LDs.

Analysis of differential gain in InGaAs-InGaAsP compressive and tensile strained quantum-well lasers and its application for estimation of high-speed modulation limit

A simplified model that furnishes an intuitive insight for the change in quantum-well (QW) laser gain due to QW strain and quantum confinement is presented. Differential gain for InGaAs-InGaAsP compressive and tensile strained multi-quantum-well (MQW) lasers is studied using the model. The comparison between the calculated and experimental results for lattice-matched and compressive strained MQW lasers shows that this model also gives quantitatively reasonable results. It is found that the variance-band barrier height strongly affects the differential gain, especially for compressively strained MQW lasers. The tensile strained MQW lasers are found to have quite high differential gain, due to the large dipole matrix element for the electron-light-hole transition, in spite of the large valence-band state density. Furthermore, a great improvement in the differential gain is expected by modulation p doping in the tensile strained MQW lasers. The ultimate modulation bandwidth for such lasers is studied using the above results. >

Temperature characteristics of a vertical-cavity surface-emitting laser with a broad-gain bandwidth

Temperature-insensitive characteristics are of great importance in implementing the actual applications of vertical-cavity surface-emitting lasers (VCSELs) because of the temperature change in the surroundings. To extend the operational temperature range of such lasers, we fabricated a VCSEL with a broad gain bandwidth. The active layers in VCSELs consist of multiple quantum wells (MQWs) with different bandgap energies. From the change in the threshold current, with temperature as a parameter, we found that the operational temperature range of a VCSEL with a broad gain bandwidth is more than 20/spl deg/C wider than that of conventional VCSELs, whose active layers consist of a single type of MQW. We demonstrate that the extended-gain bandwidth gives better temperature characteristics. In addition, we simulated the structure of the active layers, and the optimized structure resulted in a 1-mW light output power at less than 5 mA in a single transverse mode oscillation from 20-70/spl deg/C. >

Reflectance spectroscopy on GaN films under uniaxial stress

The uniaxial stress effects on valence band structures in GaN are investigated by reflectance spectroscopy. It is observed that the energy separation between A and B valence bands increases with the application of uniaxial stress in the c plane. The experimental results are analyzed on the basis of the k⋅p theory, and deformation potential D5 is determined as −3.3 eV. It is indicated that the uniaxial strain effect could be utilized for improving GaN-based laser performance.

Effect of Biaxial Strain on Cubic and Hexagonal GaN Analyzed by Tight-Binding Method

The effect of tensile and compressive biaxial strain on the valence band structures around the valence band edge, for both cubic and hexagonal GaN, were analyzed using a tight-binding method, which took the spin-orbit interaction into account. Biaxial strain was induced in the (001) and (0001) plane for cubic and hexagonal GaN, respectively. The strain induced change in the band structures was qualitatively the same for two types of GaN, however, it was remarkably different compared with GaAs, due to the very small split-off energy in GaN. The advantages of tensile strained GaN semiconductor lasers were discussed.

Γ‐ and X‐band contributions to nonresonant tunneling in GaAs/Al0.35Ga0.65As double quantum wells

Time‐resolved photoluminescence in the picosecond regime is performed on an asymmetric GaAs/Al0.35Ga0.65As double quantum well structure with a barrier thickness of 6 nm to obtain the Γ‐ and X‐point barrier contributions to nonresonant tunneling. Application of hydrostatic pressure up to 37 kbar at 5 K reveals that tunneling via virtual X states is at least 800 times less efficient than via virtual Γ states. Above 24.5 kbar an extremely fast scattering of electrons out of the n=1 quantized level of the narrower quantum well is observed.

100-Gbps CMOS transceiver for multilane optical backplane system with a 1.3 cm 2 footprint

A compact 25-Gbps × 4-channel optical transceiver has been fabricated for optical backplane systems. Power consumption was as low as 20 mW/Gbps. A transmission experiment was successfully conducted at 25 Gbps.

Single domain hexagonal GaN films on GaAs (100) vicinal substrates grown by hydride vapor phase epitaxy

Hexagonal GaN ( h-GaN) films are grown on GaAs (100) vicinal substrates by hydride vapor phase epitaxy. The substrate misorientation dependence of the crystal structure is investigated by X-ray diffraction measurements using a 4-circle diffractometer. It is found that misorientation toward the B direction is essential for the growth of single domain h-GaN films and that the c-axis of the single domain h-GaN orients to the GaAs B direction.