Growth and Characterization of GaN Underlying Layer Used in Blue-Violet GaN-Based Laser Diodes on Sapphire
- PDF / 409,411 Bytes
- 9 Pages / 612 x 792 pts (letter) Page_size
- 21 Downloads / 207 Views
Growth and Characterization of GaN Underlying Layer Used in Blue-Violet GaN-Based Laser Diodes on Sapphire Kenji Funato, Tomonori Hino1, Shigetaka Tomiya2, Takao Miyajima, Takeharu Asano1, Tsyuyoshi Tojyo1, Shigeki Hashimoto, Katsunori Yanashima, Shiro Uchida1, Koshi Tmamura, Toshimasa Kobayashi, and Masao Ikeda1 Core Technology Development Center, Sony Corporation Core Technology & Network Company, Yokohama Research Center 2-1-1 Shinsakuragaoka Hodogaya-ku, Yokohama-shi, Kanagawa, 240-0036, Japan 1 Development Center, Sony Shiroishi Semiconductor Inc. 3-53-2 Shiratori, Miyagi, 989-0734, Japan 2 Environment & Analysis Technology Department, Technical Support Center, Yokohama Research Center, Sony Corporation 2-1-1 Shinsakuragaoka Hodogaya-ku, Yokohama-shi, Kanagawa, 240-0036, Japan ABSTRACT The underlying GaN layers on which laser diodes are fabricated have been improved through two steps. In the first step, GaN single layer on sapphire was investigated. The residual strain and etch pit density were measured. We found that they reflect the optical quality. We found that the threading dislocation can be reduced to 4 x 108 cm-2. The optical quality depends on the residual strain and dislocation density. In the next step, we have utilized epitaxial lateral overgrowth (ELO) technique. The optimized GaN layer on sapphire with the smallest dislocation density was used as seed layer. In the wing region of ELO-GaN, the threading dislocation density was reduced to 1 x 106 cm-2. On the other hand, in the seed region, dislocation density remained 4 x 108 cm-2. Photoluminescence intensity in the wing region was three times as large as that in the seed. The laser diodes were fabricated on the ELO-GaN layer, so that the ridge stripe was fabricated over the wing region, and its properties were compared with those of laser diodes on sapphire. It was found that the lifetime can be increased by using the ELO-GaN layer as the underlying layer.
INTRODUCTION GaN-based laser diodes (LDs) are promising for the light source of high-density optical data storage system. The continuous-wave (CW) operation at room temperature was achieved in 1996 [1], for LD grown on sapphire. The lifetime more than 10000 hours has been achieved [2] by using epitaxial lateral overgrowth (ELO) technique [3,4]. The threading dislocation density can be dramatically reduced by ELO. This suggests that the reduction of threading dislocation density is effective for improvement of the lifetime. In the present paper, we will report our approach to the reduction of the threading dislocation density of the GaN underlying layer on which LD structure is grown. The approach was composed of two steps. In the first step, the GaN single layer on the sapphire substrate was improved. We used raised-pressure metalorganic chemical vapor deposition (RP-MOCVD) in which the growth pressure can be set more than atmospheric pressure [5]. The residual strain was estimated by measuring lattice constants with x-ray diffraction. The residual strain was caused by difference between therma
Data Loading...
