Blue light-emitting diode based on ZnO

TL;DR

This paper reports on the development of a blue light-emitting diode using ZnO p-i-n homojunctions, demonstrating electroluminescence at 440 nm and analyzing charge injection and resistance issues.

Contribution

It introduces a ZnO-based blue LED with observed electroluminescence and discusses the charge injection imbalance and series resistance challenges.

Findings

Electroluminescence peak at 440 nm matches photoluminescence of p-ZnO.

Electron injection from n-ZnO to p-ZnO dominates the emission.

Series resistance of several hundred ohms affects device performance.

Abstract

A near-band-edge bluish electroluminescence (EL) band centered at around 440 nm was observed from ZnO p-i-n homojunction diodes through a semi-transparent electrode deposited on the p-type ZnO top layer. The EL peak energy coincided with the photoluminescence peak energy of an equivalent p-type ZnO layer, indicating that the electron injection from the n-type layer to the p-type layer dominates the current, giving rise to the radiative recombination in the p-type layer. The imbalance in charge injection is considered to originate from the lower majority carrier concentration in the p-type layer, which is one or two orders of magnitude lower than that in the n-type one. The current-voltage characteristics showed the presence of series resistance of several hundreds ohms, corresponding to the current spread resistance within the bottom n-type ZnO. The employment of conducting ZnO substrates may solve the latter problem.