Author: John Anthony Buckeridge

Publisher:

Published: 2010

Total Pages: 217

ISBN-13:

The focus of this work is an investigation of the local structure of nitrogen-related defects in the dilute nitride semiconductor, GaNxAs1-x. 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 1.55æm) 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, to such a degree as to render the materials unacceptable for many applications at present. 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 sharing Ga nearest-neighbours, with energies very close to the conduction band edge. We calculate methods of probing defects associated with substitutional N in GaAs. In particular we present results of first-principles density functional theory calculations on the localized vibrational mode (LVM) spectrum of the Si-N defect in GaAs, and the effects of strain on the isolated nitrogen LVM. A gated, double-quantum-well InGaAs/GaNxAs1-x heterostructure device, in which the interaction between conduction band carriers and states associated with clusters of nitrogen atoms, 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 lie near the GaAs conduction band edge and are considered to be the primary mobility-limiting factor in the dilute nitrides.