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.
@article{arxiv.cond-mat/0504587,
title = {Blue light-emitting diode based on ZnO},
author = {Atsushi Tsukazaki and Masashi Kubota and Akira Ohtomo and Takeyoshi Onuma and Keita Ohtani and Hideo Ohno and Shigefusa F. Chichibu and Masashi Kawasaki},
journal= {arXiv preprint arXiv:cond-mat/0504587},
year = {2009}
}