title: The effect of free-standing GaN substrate on carrier localization in ultraviolet InGaN light-emitting diodes.
abstract: In this study, we have grown 380-nm ultraviolet light-emitting diodes (UV-LEDs) based on InGaN/AlInGaN multiple quantum well (MQW) structures on free-standing GaN (FS-GaN) substrate by atmospheric pressure metal-organic chemical vapor deposition (AP-MOCVD), and investigated the relationship between carrier localization degree and FS-GaN. The micro-Raman shift peak mapping image shows low standard deviation (STD), indicating that the UV-LED epi-wafer of low curvature and MQWs of weak quantum-confined Stark effect (QCSE) were grown. High-resolution X-ray diffraction (HRXRD) analyses demonstrated high-order satellite peaks and clear fringes between them for the UV-LEDs grown on the FS-GaN substrate, from which the interface roughness (IRN) was estimated. The temperature-dependent photoluminescence (PL) measurement confirmed that the UV-LEDs grown on the FS-GaN substrate exhibited better carrier confinement. Besides, the high-resolution transmission electron microscopy (HRTEM) and energy-dispersive spectrometer (EDS) mapping images verified that the UV-LEDs on FS-GaN have fairly uniform distribution of indium and more ordered InGaN/AlInGaN MQW structure. Clearly, the FS-GaN can not only improve the light output power but also reduce the efficiency droop phenomenon at high injection current. Based on the results mentioned above, the FS-GaN can offer UV-LEDs based on InGaN/AlInGaN MQW structures with benefits, such as high crystal quality and small carrier localization degree, compared with the UV-LEDs on sapphire.
authors.affiliation: Department of Electrophysics, National Chiao Tung University, 1001 Ta Hsueh Road, Hsinchu, 30010, Taiwan, allen_ken@hotmail.com.
authors.forename: Ming-Ta
authors.initials: MT
authors.lastname: Tsai
authors.forename: Chung-Ming
authors.initials: CM
authors.lastname: Chu
authors.forename: Che-Hsuan
authors.initials: CH
authors.lastname: Huang
authors.forename: Yin-Hao
authors.initials: YH
authors.lastname: Wu
authors.forename: Ching-Hsueh
authors.initials: CH
authors.lastname: Chiu
authors.forename: Zhen-Yu
authors.initials: ZY
authors.lastname: Li
authors.forename: Po-Min
authors.initials: PM
authors.lastname: Tu
authors.forename: Wei-I
authors.initials: WI
authors.lastname: Lee
authors.forename: Hao-Chung
authors.initials: HC
authors.lastname: Kuo