The effect of point defects on the dielectric properties of semiconductor materials: structure, charge, and concentration.
ORAL
Abstract
Dielectric effects have been shown to be important to many material and device properties. Despite this, little work has been done examining in detail the effects of defects in semiconductors on the dielectric response. We calculate the dielectric response of GaAs as a function of photon energy in the presence of all intrinsic point defects for a range of charge states. In the case of intrinsic point defects, we consider multiple configurations to study the effect of the defect structure on dielectric behavior, which may be relevant in non-equilibrium conditions. The effects of defects on the matrix elements and energy levels as they pertain to the dielectric behavior are also examined.
The presence of point defects is found to produce the strongest deviation in dielectric behavior from the pristine behavior at low photon energies. This most significantly manifests in the common, though not universal, creation of an Urbach tail in the dielectric function. This tail is found to be related almost entirely to the effects of defect induced states off the Gamma-point in the GaAs band-structure. The charge state of the defect is found to have significant effects on the dielectric response of GaAs, particularly at low frequencies where an Urbach tail may be present. The effect of defect structure on the dielectric function to be strongest at low frequencies and was found to be able to change the dielectric response by as much as twenty-five percent with comparatively smaller effects on the shape of the dielectric function.
We also present an examination of the effect of decreasing defect density on the contributing factors to our model of dielectric behavior. In service of this goal, we propose a new method for calculating the dielectric function of a material with more realistic point defect concentrations (of order 1/10000 or less) which are far beyond the scope of regular DFT calculations. Experemental results have shown that dielectric properties can be appreciably affected by defect concentrations in this regime.
The presence of point defects is found to produce the strongest deviation in dielectric behavior from the pristine behavior at low photon energies. This most significantly manifests in the common, though not universal, creation of an Urbach tail in the dielectric function. This tail is found to be related almost entirely to the effects of defect induced states off the Gamma-point in the GaAs band-structure. The charge state of the defect is found to have significant effects on the dielectric response of GaAs, particularly at low frequencies where an Urbach tail may be present. The effect of defect structure on the dielectric function to be strongest at low frequencies and was found to be able to change the dielectric response by as much as twenty-five percent with comparatively smaller effects on the shape of the dielectric function.
We also present an examination of the effect of decreasing defect density on the contributing factors to our model of dielectric behavior. In service of this goal, we propose a new method for calculating the dielectric function of a material with more realistic point defect concentrations (of order 1/10000 or less) which are far beyond the scope of regular DFT calculations. Experemental results have shown that dielectric properties can be appreciably affected by defect concentrations in this regime.
*This work is supported by the Laboratory Directed Research and Development program of Los Alamos National Laboratory.
–
Publication: Planned Papers (titles provisional): Optical Properties of GaAs in the Presence of Point Defects, Dielectric Permittivity of GaAs with Realistic Defect Concentrations.
Presenters
-
Stephen Fluckey
- Los Alamos National Laboratory (LANL)