Abstract
In this study, indium-tin oxide (ITO)/Al-doped zinc oxide (AZO) composite films were fabricated by pulsed laser deposition and used as transparent contact layers (TCLs) in GaN-based blue light emitting diodes (LEDs). The ITO/AZO TCLs were composed of the thin ITO (50 nm) films and AZO films with various thicknesses from 200 to 1000 nm. Conventional LED with ITO (200 nm) TCL prepared by E-beam evaporation was fabricated and characterized for comparison. From the transmittance spectra, the ITO/AZO films exhibited high transparency above 90% at wavelength of 465 nm. The sheet resistance of ITO/AZO TCL decreased as the AZO thickness increased, which could be attributed to the increase in a carrier concentration, leading to a decrease in the forward bias of LED. The LEDs with ITO/AZO composite TCLs showed better light extraction as compared to LED with ITO TCL in compliance with simulation. When an injection current of 20 mA was applied, the output power for LEDs fabricated with ITO/AZO TCLs had 45%, 63%, and 71% enhancement as compared with those fabricated using ITO (200 nm) TCL for the AZO thicknesses of 200, 460, and 1000 nm, respectively.
Highlights
High efficiency GaN-based light-emitting diodes (LEDs) are used in a large range of potential applications such as full-color displays, traffic signals, automobiles, solid-state lighting, backlights of liquid-crystal displays, and so on [1,2,3]
composite films were fabricated by pulsed laser deposition
AZO transparent contact layers (TCLs) were composed of the thin indium-tin oxide (ITO)
Summary
High efficiency GaN-based light-emitting diodes (LEDs) are used in a large range of potential applications such as full-color displays, traffic signals, automobiles, solid-state lighting, backlights of liquid-crystal displays, and so on [1,2,3]. Indium tin oxide (ITO) has emerged as one of most promising materials for the TCL in GaN-based LEDs due to its low resistivity and high transparency in the range of visible wavelength [9,10]. 90% in both visible and UV regions [20] It indicates that the film has great potential in the TCL on LEDs. In this work, the ITO (50 nm)/AZO (200-1000 nm) films, which were grown by PLD, were characterized and used as the TCLs on GaN blue LEDs to improve light extraction efficiency. The AZO films with various thicknesses are applied for uniform current spreading, high transparent and thick window layer to achieve the highly efficient LEDs. the conventional LED with ITO (200 nm) TCL grown by Ebeam evaporation was fabricated as contrasted sample
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