Investigation of Sputtered AlN Nucleation Layer on GaN-based Light Emitting Diodes

• Main Authors: Wang, Wei-Li, 王韋力
• Other Authors: Kuo, Cheng-Huang
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/71451638416243143225

碩士 === 國立交通大學 === 照明與能源光電研究所 === 100 === The purpose of this study was to investigate the application of sputtered AlN nucleation layers in GaN-based light-emitting diodes (LEDs). We first investigated the growth mechanism and surface morphology of GaN film growth on varying thicknesses of sputtered AlN nucleation layers. Based on GaN film growth time and surface reflectivity diagrams, we used SEM to measure the surface morphology at various times, conducted analysis, and then measured GaN film quality with X-ray diffraction and AFM image of etching pits density. Finally, after employing MOCVD to grow GaN nucleation layers with GaN-based light-emitting diodes, we measured and compared the optical properties and light output power. According to SEM-measured GaN film growth on sputtered AlN nucleation layers of varying thicknesses, as the sputtered AlN thickness decreases, the 3D to 2D growth recovery time of GaN films increases and the GaN film pit density decreases. Differences in the sputtered AlN nucleation layer thicknesses also produce differences in the surface crystal nucleation densities, further affecting GaN film growth. GaN (102) full width at half maximum (FWHM) measurement analysis and etching pit density measurement results show that the X-ray (102) FWHM of GaN films grown on sputtered AlN nucleation can be reduced from 558 arcsec to 387 arcsec compared to those grown on conventional sapphire, and the etching pit density declines as the sputtered AlN nucleation layer thickness decreases. The results show that GaN films grows on sputtered AlN nucleation layers can increase the film quality. Finally, after using MOCVD to grow GaN nucleation layers with GaN-based LEDs, the current-voltage measurement system results indicate that, with an injected current of 20 mA, sputtered AlN nucleation layers and MOCVD-grown AlN nucleation layers show no significant effect on the electrical properties of LEDs. The current-voltage curves adopted by the current-voltage measurement system under reverse bias verify that reducing the nucleation layer thickness can increase GaN film quality and further improve leakage current values. With an injected current of 20 mA, increasing from 3.40 mW to 4.53 mW, the light output power was increased by 33%. This demonstrates that AlN film nucleation layers can effectively reduce the etching pit density caused by incompatible GaN films and sapphire lattice constants, improving GaN film quality and increasing internal quantum efficiency and light output power.