標題: InGaN-based light-emitting diodes grown on various aspect ratios of concave nanopattern sapphire substrate
作者: Ke, Wen-Cheng
Chiang, Chih-Yung
Son, Widi
Lee, Fang-Wei
電子物理學系
Department of Electrophysics
關鍵字: LED;Nanoscale-patterned sapphire substrate;Anodic aluminum oxide;Diffuse transmittance;Aspect ratio
公開日期: 31-十月-2018
摘要: This study presented the optoelectronic properties of InGaN-based light-emitting diodes (LEDs) grown on nanoscale-patterned sapphire substrates (NPSSs) with various aspect ratio (AR) concave nanopatterns. Concave nanopatterns with low ARs of similar to 0.5 (LAR-NPSS) and high ARs of 2, 3 and 4 (HAR-NPSS) were achieved using an anodic aluminum oxide template as the dry etching mask. The diffuse transmission (DT) rate of the incident light wavelength at 450 nm increased linearly, from 2.2% for LAR-NPSS to 12.7% for HAR-NPSS with an AR of 4. However, the diffuse reflection (DR) rate for HAR-NPSS did not increase linearly with the increasing AR values. The limit of the DR rate for HAR-NPSS could be attributed to the guiding effect when the incident light entered into the high AR concave nanopattern; most of the incident light could not be reflected (returned to the air), therefore there was no significant contribution to the DR rate. The luminous intensities of LEDs grown on bare sapphire (B-LED), HAR-NPSS (HAR-LED) and LAR-NPSS (LAR-LED) were 39, 38 and 74 mcd, respectively. Interestingly, the lowest brightness of any LED was the HAR-LED, which had higher DT and DR rates. This significant discrepancy could be attributed to a large number of voids occurring at the initial growth stage of the LED epitaxial layer on the HAR-NPSS that caused the emitted photons to remain trapped inside the LED. In addition, increasing the LED epilayer coverage area (i.e. 1.6-fold) with the inclined facets of low AR concave nanopatterns effectively scattered the emitted photons, leading to an increased light emitting intensity of the LED. The experimental results indicated that the specific AR concave nanopattern of an NPSS could increase the LED epitaxial layer coverage area and prevent void formation, which plays a crucial role in achieving high-brightness in InGaN-based LEDs.
URI: http://dx.doi.org/10.1016/j.apsusc.2018.06.223
http://hdl.handle.net/11536/147986
ISSN: 0169-4332
DOI: 10.1016/j.apsusc.2018.06.223
期刊: APPLIED SURFACE SCIENCE
Volume: 456
起始頁: 967
結束頁: 972
顯示於類別:期刊論文