Transparent current spreading layers for optoelectronic devices

In this paper we develop a simple model based on a leaky transmission line to assess the electrical performance of transparent current spreading layers for application to surface light emitting diodes. Figures of merit suitable for device design are obtained and these are applied to a range of material systems reported in the literature. These calculations show that materials with electrical characteristics approaching ultimate performance limits can be achieved. Furthermore, calculations of the electromagnetic absorption of conducting layers show that further improvements should be possible by selecting materials with the highest possible majority carrier mobilities, which enable films of greater thickness to be grown while maintaining high transparency, leading to very low spreading layer resistances. Ways of achieving improved mobility are also discussed.