High-performance InGaN/GaN MQW LEDs with Al-doped ZnO transparent conductive layers grown by MOCVD using H ₂ O as an oxidizer

Abstract

In this study, the high performance of InGaN/GaN multiple quantum well light-emitting diodes (LEDs) with Aldoped ZnO (AZO) transparent conductive layers (TCLs) has been demonstrated. The AZO-TCLs were fabricated on the n + -InGaN contact layer by metal organic chemical vapor deposition (MOCVD) using H 2 O as an oxidizer at temperatures as low as 400 • C without any post-deposition annealing. It shows a high transparency (98%), low resistivity (510 −4 Ω•cm), and an epitaxial-like excellent interface on p-GaN with an n + -InGaN contact layer. A forward voltage of 2.82 V @ 20 mA was obtained. Most importantly, the power efficiencies can be markedly improved by 53.8%@20 mA current injection and 39.6%@350 mA current injection compared with conventional LEDs with indium tin oxide TCL (LED-III), and by 28.8%@20 mA current injection and 4.92%@350 mA current injection compared with LEDs with AZO-TCL prepared by MOCVD using O 2 as an oxidizer (LED-II), respectively. The results indicate that the AZO-TCL grown by MOCVD using H 2 O as an oxidizer is a promising TCL for a low-cost and high-efficiency GaN-based LED application.

Effect of graphene/ZnO hybrid transparent electrode on characteristics of GaN light-emitting diodes

“…Therefore, in the present work the transmittance was chosen as an alternative comparison reference. The measured transmittances of 200 nm AZO, 280 nm GZO, 440 nm IZO, and 1L-3L Gr at the wavelength of 550 nm have been measured and reported by Park et al, [17] Lin et al, [18] Lameche et al, [19] and Li et al, [34] respectively. Thus, the calculated and experimental transmittances of these six kinds of TCLs were compared, and the results are given in Fig.…”

“…Generally, the undoped ZnO film has a low carrier concentration and a high resistivity, and thus In, aluminum (Al), and gallium (Ga) are often applied to dope ZnO to improve the conductivity. [17][18][19] Therefore, three kinds of ZnO, i.e. Al-,Ga-, and In-doped ZnO (AZO, GZO, and IZO, respectively), are observed in this paper.…”

“…Thus, in order to get precise calculated results, the actual refractive index of various doped ZnO should be chosen. Typically, the refractive indices of Gr, IZO, AZO, and GZO are taken as n = 2.24 + 0.07i, [34] 1.97 + 0.01i, [17] 1.91 + 0.05i, [18] and 1.87 + 0.01i, [19] respectively. The transmission of TCLs is equal to the ratio of the square of the electric field strength.…”