AbstractThe electronic and transport properties of doped and undoped arsenic triselenide have been characterised in an extensive study. Measurement of optical absorption, d.c, conductivity, thermoelectric power and fast charge transient photoconductivity were made. In addition, an improved time of flight technique and a modulated steady state photocurrent experiment were developed.
Results obtained from undoped, vitreous, evaporated and sputtered samples were explained on the basis of a multiple trapping transport model with trap levels E2 (0.62eV) and E3 (0.42eV) above the valence band edge.
Variation of the dispersion parameter with temperature in vitreous material supports the presence of structure at E2 in the distribution of localised states N(E). Deviations from power law behaviour in the transient photodecay also suggest a structured N(E) and a computer simulation of the thermalisation process was developed in order to obtain N(E) from the data. For sputtered material a feature incorporated at E3 in a continuous tail of states gave the the best fit to the data. Determination of N(E) using two other recently developed spectroscopic techniques also gave excellent agreement in the energy position E3.
The spectroscopic analysis offered a new technique for obtaining values of the capture coefficient C and offers the possibility of obtaining the energy dependence of C (if any).
In nickel doped specimens the Fermi-level was shifted by as much as 0.6eV, the conductivity increased by 11 orders of magnitude and n-type conduction, rarely seen in chalcogenides, observed. These unique findings were explained by inclusion of an acceptor level (E4 0.22eV), introduced by nickel, into the intrinsic model density of states.
Results obtained when incorporating indium infer a shift in the valence band edge by 0.03 eV rather than a shift of the Fermi-level. A decrease in the trap density at E3 with increasing indium content is also inferred.
|Date of Award||Mar 1985|