Carrier Mobility-lifetime Product Research Articles

Photocarrier Transport and Recombination in Amorphous Silicon

The effect of microstructure in undoped a-Si:H films on carrier transport, recombination, densities of midgap states and solar cell characteristics has been investigated. Extended state mobilities of electrons were obtained from photo and dark conductivity measurements between 40° C and 190° C and the gap states characterized using Dual Beam Photoconductivity. In these films the estimated room temperature electron mobilities increase from about 1 to 30 cm2/V sec as the dihydride concentrations and void volume fractions decrease. It is found that the carrier mobility-lifetime products are not solely determined by the dangling bond states. The effects of changes in the mobilities and midgap states on p-i-n homojunction solar cell characteristics are presented and discussed.

Improvements in Thallium Bromoiodide Photodetectors for Scintillation Spectrometers

ABSTRACTThallium bromoiodide, a tuneable band gap semiconductor system, was investigated as a photodetector for scintillation spectrometers. Extensive zone refining of starting materials, based on numerical simulations, considerably enhanced the electrical resistivity to 1011 Ωcm. In addition, accelerated crucible rotation technique (ACRT) crystal growth and after-growth annealing have improved the charge carrier mobility-lifetime product. However, a relatively low signal-to-noise ratio due to a high dielectric constant and relatively low quantum efficiency continues to be an obstacle to achieving high performance, large area T1BrxI1−xphotodetectors.

Schottky Barriers on a-Si:H,F/a-Si,Ge:H,F Superlattices

AbstractWe report measurements of Schottky barrier heights and minority carrier mobilitylifetime products of multilayer structures composed of a-Si:H,F and a-Si,Ge:H,F. These layers are grown by r.f. glow discharge decompostion of SiF4, GeF4, and H2 in the a-Si,Ge:H,F (well) layer and of SiF4 and H2 in the a-Si:H,F (barrier) layer.Schottky barrier height ΦB of Pt is measured using internal photoemission measurements. The minority carrier mobility-lifetime product (μτ)p is extracted from a fit of the voltage dependence of internal quantum efficiency to the Hecht expression. Both ΦB and (μτ)p are measured as a function of barrier and well thicknesses.

Energy dependence of the carrier mobility-lifetime product in hydrogenated amorphous silicon

The results of optical-absorption measurements determined by photothermal deflection spectroscopy, primary photoconductivity, and secondary photoconductivity on undoped and phosphorus-doped hydrogenated amorphous silicon films (a-Si:H) are reported. A normalization procedure for obtaining photocurrent spectra at constant generation rate is demonstrated. From these measurements, the efficiency-mobility-lifetime product (eta..mu..tau) for electrons is found to be constant from 2.0 to approx.0.9 eV for both undoped and phosphorus-doped a-Si:H. For excitations less than approx.0.9 eV, there is evidence that the product eta..mu..tau for electrons drops rapidly; similarly, the eta..mu..tau for holes exhibits a rapid decrease in undoped material for photon energies less than approx.1.5 eV. A model is proposed to explain the results, resolving a discrepancy between secondary- and primary-photoconductivity measurements of the optical absorption.