• Chinese Optics Letters
  • Vol. 20, Issue 3, 031402 (2022)
Lei Han1、2、3, Yuanbin Gao1、2、3, Sheng Hang1、2、3, Chunshuang Chu1、2、3、*, Yonghui Zhang1、2、3, Quan Zheng4, Qing Li4, and Zi-Hui Zhang1、2、3、**
Author Affiliations
  • 1State Key Laboratory of Reliability and Intelligence of Electrical Equipment, Hebei University of Technology, Tianjin 300401, China
  • 2Key Laboratory of Electronic Materials and Devices of Tianjin, School of Electronics and Information Engineering, Hebei University of Technology, Tianjin 300401, China
  • 3Hebei Key Laboratory of Advanced Laser Technology and Equipment, Tianjin 300401, China
  • 4Key Engineering Center of Flat-Panel-Display Glass and Equipment, Shijiazhuang 050035, China
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    Abstract

    The hole injection capability is essentially important for GaN-based vertical cavity surface emitting lasers (VCSELs) to enhance the laser power. In this work, we propose GaN-based VCSELs with the p-AlGaN/p-GaN structure as the p-type hole supplier to facilitate the hole injection. The p-AlGaN/p-GaN heterojunction is able to store the electric field and thus can moderately adjust the drift velocity and the kinetic energy for holes, which can improve the thermionic emission process for holes to travel across the p-type electron blocking layer (p-EBL). Besides, the valence band barrier height in the p-EBL can be reduced as a result of usage of the p-AlGaN layer. Therefore, the better stimulated radiative recombination rate and the increased laser power are obtained, thus enhancing the 3 dB frequency bandwidth. Moreover, we also investigate the impact of the p-AlGaN/p-GaN structure with various AlN compositions in the p-AlGaN layer on the hole injection capability, the laser power, and the 3 dB frequency bandwidth.

    1. Introduction

    Due to the advantages of low threshold current, single longitudinal mode output, easy process for packaging, wafer level testing, and circular output beams[1], vertical cavity surface emitting lasers (VCSELs) have shown tremendous application potential in data communication, retinal scanning displays, medical laser, high density optical storage, printing and optical scanners, etc.[24]. Since the first, to the best of our knowledge, room-temperature electrically injected GaN-based VCSEL was achieved in 2008[5], great efforts have been made to achieve better lasing performance for GaN-based VCSELs[68]. However, the development of GaN-based VCSELs still faces quite a few challenges. One of the obstacles that hinder the lasing performance is lateral optical mode confinement. Lateral optical mode confinement can be realized by using the buried SiO2 layer below indium-tin-oxide (ITO), where the design can also reduce the internal loss[9]. However, an even easier method to achieve the lateral mode confinement is locally varying the cavity length, and therefore a nano-height cylindrical waveguide structure has been reported[10]. Another obstacle that hinders the improvement for the laser power is low hole injection, which arises from the current crowding effect at the aperture periphery and the hole blocking effect by the p-AlGaN electron blocking layer (p-EBL). For the purpose of shaping the current paths for VCSELs, a tunnel-junction VCSEL and a VCSEL with a p-GaN/n-GaN/p-GaN structured current spreading layer are proposed to increase the current injection into the aperture[11,12]. Besides, the AlGaN/GaN multiple-quantum-barrier structured p-EBL and Al composition-graded p-EBL have been reported, which can promote the hole injection efficiency by reducing the valence band barrier height of p-EBL[13,14].