Theoretical study of local defect structures in dilute nitride semiconductors

Abstract

Dilute nitride alloys have attracted considerable attention in recent years. When a small fraction of the As atoms in GaAs or InGaAs are replaced by N, the energy gap of the material decreases rapidly; for example by 150 meV when the N concentration is 1%, making it a promising material for long wavelength (1.3 and 1.5 micron) telecommunications lasers based on a GaAs substrate and for extending the wavelength range of GaAs-based solar cells further into the infrared. However, the addition of these small concentrations of nitrogen to GaAs has also been found to cause a drastic reduction in n-type carrier mobility. The reductions in band gap and carrier mobility are attributed to an interaction between the GaAs conduction band, and a set of localized or quasi-localized defect states associated with the substitution of N on As sites at random throughout the alloy. The drastically low mobility in particular is attributed to the interaction with localized defect states associated with clusters of N atoms, whose energies are near-resonant with the conduction band edge. We calculate methods of probing defects associated with substitutional N in GaAs. A gated, double-quantum-well InGaAs/GaNAs heterostructure device, in which the interaction between conduction band carriers and states associated with N complexes, forming at random throughout the alloy, can be tuned by varying the gating electric fields, is described. The mobility as a function of gate field is calculated, with reductions in mobility occurring when the Fermi level is resonant with the energies of the N cluster states, providing a possible experimental method of probing these states, which are considered to be the primary mobility-limiting factor in the dilute nitrides.

John Buckeridge

Lecturer in Energy Engineering and Materials Devices

Materials physicist working at the School of Engineering - Division of Electrical and Electronic Engineering, London South Bank University.