Computation of photoconductivity in insulators in the space charge and recombination regime: Application to PbO films

Abstract

Exact solutions for the photoconductivity of insulators with space charge (caused by deep trapping) and recombination require numerical methods for solving coupled, nonlinear differential equations. A method for obtaining computer solutions is outlined and the parameters required for fitting existing data for the photoconductor PbO are given. The carrier lifetimes are found to be much longer than previously assumed and the recombination coefficients for free with trapped carriers are found to be very large, close to diffusion controlled. The predictions for the time required to achieve steady state were found to be unexpectedly long, a result of the feedback between trapping and recombination.

Lead monoxide α-PbO: electronic properties and point defect formation

“…First-principles density-functional calculations were used to calculate the electronic properties of polycrys- The presence of defects and differential trapping of electrons and holes were predicted by others to explain space charge limited photoconductivity in PbO [4] and to model x-ray sensitivity, modulation transfer function (MTF) and detective quantum efficiency (DQE) of the PbO x-ray detector [6]. The results presented here agree well with these studies and provide insight into the nature of defects in PbO clarifying their electronic and charge states and explaining why vacancies exist in high concentration in thermally evaporated PbO layers.…”

“…PbO satisfies the first three criteria. However, thick PbO does not show adequate transport properties and this results in poor temporal characteristics (signal propagation/delay time) [2,4]. This is the primary issue in the development of PbO in x-ray medical imaging detectors.…”

Charge carrier injection into insulating media: Single-particle versus mean-field approach

“…By the simulation of inorganic and organic semiconductor devices the fixed values of charge carrier densities at the boundary with the insulating region are often used as boundary conditions [1][2][3][4][5][6] . For charge transport in bulk dielectrics the electric field at the injecting interface is often taken equal to zero assuming space-charge limitation of the current [7][8][9][10] .…”

Anisotropy of the carrier effective masses in bulk α -PbO

“…Experimental data exists only in restricted domains (i.e., mobility-lifetime product) and reliability has not been established. The carrier mobilities have only been roughly estimated [3]. Some efforts have been made to define the band structure and density of states (with an emphasis on orbital hybridization) [4][5][6][7], but the carrier effective masses remain unknown.…”