Masayuki Sonobe

Dislocation-Free m-Plane InGaN/GaN Light-Emitting Diodes on m-Plane GaN Single Crystals

m-Plane (10-10) nonpolar InGaN-based light emitting diodes (LEDs) with no threading dislocations or stacking faults have been realized on m-plane GaN single crystals by conventional metal organic vapor phase epitaxy. The crystalline properties of the material, together with the structures of the LED devices, have been observed by scanning transmission electron microscopy. It is shown that dislocation-free nonpolar nitride layers with smooth surfaces can be obtained under growth conditions involving high V/III ratios, which are the optimized growth conditions for c-plane GaN. The peak wavelength of the electroluminescence emission obtained from the finished devices is 435 nm, which is in the blue region. The output power and the calculated external quantum efficiency are 1.79 mW and 3.1%, respectively, at a driving current of 20 mA.

Improved External Efficiency InGaN-Based Light-Emitting Diodes with Transparent Conductive Ga-Doped ZnO as p-Electrodes

Transparent conductive Ga-doped ZnO (ZnO:Ga) was fabricated to serve as p-contacts of InGaN-based light-emitting diodes (LEDs) using molecular-beam epitaxy. As-grown ZnO:Ga films typically have resistivities of ?=2-4?10-4 ??cm, and over 80% transparency in the near UV and visible wavelength ranges. The current-voltage characteristics between as-grown ZnO:Ga contacts and p-GaN layers were ohmic. The brightness of LEDs fabricated with ZnO:Ga p-contacts was nearly double compared to LEDs with conventional Ni/Au p-contacts. We obtained the external efficiency as high as 20.8% in the case of the near UV LED. The forward voltage at 20 mA was found not to increase even after the lamp LED with ZnO:Ga were kept for 80 h in high humidity and high temperature environments.

Optical Gain and Optical Internal Loss of GaN-Based Laser Diodes Measured by Variable Stripe Length Method with Laser Processing

We demonstrate a new technique for the variable stripe length (VSL) method by which the optical gain and optical internal loss of GaN-based laser diodes (LDs) can be directly measured. In the technique, the laser processing is utilized for varying the excitation length. The excitation length of GaN-based LDs can be varied by directly processing its p-electrode with high-power laser irradiation. From the results of the measurements, it was revealed that the optical internal loss of GaN-based LDs was strongly affected by the layer structure.