Session X29 - Wide Bandgap Semiconductors V: GaN and Related Materials.
FOCUS session, Thursday afternoon, March 15
Room 617, Washington State Convention Center, Seatle, WA

14:30
Effect of alloy nanostructure on the electronic properties of GaAsN, GaPN, and InGaN alloys
Paul Kent (National Renewable Energy Laboratory, Golden, Colorado 80401)

The III-V nitrides (GaAsN, InGaN) have emerged as a novel class of semiconductor alloys with important optoelectronic and photovoltaic applications. The optical and electronic properties of these alloys exhibit a surprisingly strong dependence on the detailed internal nanostructure. We calculated the electronic structure of GaAsN, GaPN, and InGaN alloys using the modern, atomistic, empirical pseudopotential method with large (14,000 atom) supercells. This method fully includes the effects of atomic relaxation, strain, and multi-band coupling necessary for accurate calculations of these materials. Unlike earlier, simplified calculations or phenomenological models, these calculations demonstrate the critical dependence of the physical properties of these materials on alloy nanostructure. We find:

(1) GaAsN/GaPN: We examine the evolution and formation of the electronic properties of low nitrogen content GaAsN and GaPN alloys with increasing nitrogen concentration. On the basis of our calculations we present a model of alloy formation involving highly localized nitrogen "cluster states" inside the band gap, and "perturbed host states" inside the conduction band. The cluster states include various N-N pairs and triplets, calculated in detail. As the nitrogen composition increases, the energy of the "cluster states" is fixed, but the energy of the perturbed conduction band move down ("bowing"), overtaking one-by-one the gap levels. The ensuing conduction band edge, having both localized and delocalized features explains the anomalous effective masses, temperature and pressure dependences of these alloys.

(2) InGaN: We examine the role of composition fluctuation and "intrinsic quantum dot" formation in InGaN alloys, believed responsible for the efficient blue luminescence of these alloys. Considering an InN-rich quantum dot embedded in a random InGaN alloy, we show how the effects of dot-induced quantum confinement and alloy-induced hole localization explain the luminescence properties of currently grown InGaN material.

Supported by SC/BES/OER