Transparent electrode design for AlGaN deep-ultraviolet light-emitting diodes.

Ray- Hua Hrong,Yi-Keng Fu,Wei-Hung Kuo,Wei-Kai Wang,Yu-Yuan Zeng,Chia-Lung Tsai

doi:10.1364/oe.25.032206

Abstract

Zinc gallate (ZnGa2O4; ZGO) thin films were employed as the p-type transparent contact layer in deep-ultraviolet AlGaN-based light-emitting diodes (LEDs) to increase light output power. The transmittance of 200-nm-thick ZGO in deep-ultraviolet wavelength (280 nm) was as high as 92.3%. Two different ohmic contact structures, a dot-LED (D-LED; ZGO/dot-ITO/LED) and whole-LED (W-LED; ZGO/ITO/LED), exhibited improved light output power and current spreading compared to a conventional ITO-LED (C-LED). At an injection current of 20 mA, the D-LED and W-LED exhibited 33.7% and 12.3% enhancements in light output power, respectively, compared to the C-LED. The enhanced light output power of the D-LED can be attributed to an improvement in current spreading and enhanced light-extracting efficiency achieved by introducing ZGO/dot-ITO.

Highlights

AlGaN-based deep-ultraviolet (DUV) light-emitting diodes (LEDs) with 280-nm wavelengths attract considerable attention for use in chemical sensors, biological detection, water purification, UV curing, and so on [1,2]
Zinc gallate (ZnGa2O4; ZGO) thin films were employed as the p-type transparent contact layer in deep-ultraviolet AlGaN-based light-emitting diodes (LEDs) to increase light output power
Two different ohmic contact structures, a dot-LED (D-LED; ZGO/dot-Indium tin oxide (ITO)/LED) and whole-LED (W-LED; ZGO/ITO/LED), exhibited improved light output power and current spreading compared to a conventional ITO-LED (C-LED)

Summary

Introduction

AlGaN-based deep-ultraviolet (DUV) light-emitting diodes (LEDs) with 280-nm wavelengths attract considerable attention for use in chemical sensors, biological detection, water purification, UV curing, and so on [1,2]. It is important to develop new transparent conductive oxide (TCO) materials with wide optical bandgaps as replacements for ITO thin films to improve the performance of UV LEDs [6]. The resistivities of wide-bandgap TCO materials such as MgxZn1-xO, InxGa1-xO, and Ga2O3 are too high (on the order of 10−1~10−3) for application as TCEs in DUV LEDs [8,9,10]. Zinc gallate (ZnGa2O4; ZGO) films (composites of Ga2O3 and ZnO) have been proposed as TCO materials for use in the DUV region because of their high chemical stability and large optical bandgap of 5.12 eV. The electrical and optical properties of DUV LEDs containing ZGO-based ohmic-contact ITO TCE (ZGO:ITO) layers were investigated

Experimental

Results and Discussion

Conclusions