Violet-blue LEDs based on p-GaN/n-ZnO nanorods and their stability

Abstract

In this paper, we report a fabrication, characterization and stability study of p-GaN/n-ZnOnanorod heterojunction light-emitting devices (LEDs). The LEDs were assembled fromarrays of n-ZnO vertical nanorods epitaxially grown on p-GaN. LEDs showedbright electroluminescence in blue (440 nm), although weaker violet (372 nm) andgreen-yellow (550 nm) spectral components were also observed. The device characteristicsare generally stable and reproducible. The LEDs have a low turn-on voltage (∼5 V). Theelectroluminescence (EL) is intense enough to be noticed by the naked eye, at an injection current as lowas ∼ 40 µA (2.1 × 10 − 2 A cm − 2 at 7 V bias). Analysis of the materials, electrical and EL investigationspoint to the role of a high quality of p–n nano-heterojunction whichfacilitates a large rectification ratio (320) and a stable reverse current of 2.8 µA (1.4 × 10 − 3 A cm − 2 at 5 V). Stability of EL characteristics was investigated in detail. EL intensity showed systematicdegradation over a short duration when the LED was bias-stressed at 30 V. At smaller bias (<20 V) LEDs tend to show a stable and repeatable EL characteristic. Thus a simple lowtemperature solution growth method was successfully exploited to realize nanorod/filmheterojunction LED devices with predictable characteristics.