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.
Highlights
The InGaN-based ultraviolet light-emitting diodes (UVLEDs) with wavelength ranging from 350 to 400 nm have received enormous attention for practical application, such as bio-sensor, high density storage, and shorthaul optical communication [1,2]
The epitaxial structure of the ultraviolet light-emitting diodes (UV-LEDs) was grown on both substrates, comprising a 2.5-μm-thick nGaN epilayer grown at 1,150°C, a 12-period InGaN/ AlInGaN multiple quantum well (MQW) active layer grown at 830°C, 15-nmthick Mg-doped Al0.3Ga0.7N electron blocking layers (EBLs) grown at 1,030°C, and a 100-nm-thick p-GaN layer grown at 1,030°C
The uniform, well-defined, and long crystallographic steps can be observed on the top surface of UV-LEDs on free-standing GaN (FS-GaN), suggesting that the UV-LEDs based on InGaN/AlInGaN MQWs of excellent quality are grown
Summary
The InGaN-based ultraviolet light-emitting diodes (UVLEDs) with wavelength ranging from 350 to 400 nm have received enormous attention for practical application, such as bio-sensor, high density storage, and shorthaul optical communication [1,2]. The white-light LEDs (WLEDs) can be realized by using InGaN-based UVLED chip which excited the phosphor of red, green, and blue (RGB) [3]. Compared with the case of white-light emission from yellow phosphor with blue LED chip, many researches pointed out that the InGaN-based UV-LED has many excellent properties, such as lower wavelength shift as increasing injection current, high luminous efficiency, white point determined by phosphor only, better color that high crystalline quality epilayer could dramatically improve the device performance. We examine the effect of FS-GaN on the growth of UV-LEDs based on the InGaN/AlInGaN MQW structure with the characterizations of interface structure and optical properties being emphasized
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