Abstract
Experimental and theoretical studies have been made of low and high field electron transport in n-type In AS1-X PX as a function of alloy composition and hydrostatic pressure. With the electron concentration and Hall mobility varying from 6 x 1015cm-3 and 3500 cm2/V/s respectively in InP to 2 x 1016cm-3 and 12500 cm2/V/s in In As, the total density of impurity was found to vary from about 1016cm-3 in InP to about 1017cm-3 in In As showing that impurity scattering became increasingly important with decreasing phosphorus content. A decrease in mobility with increasing pressure was observed. Taking the measured density of impurities, the variation in mobility with pressure could be accounted for by the theory when both polar optical and ionized impurity scatterings were taken into account. The drift mobility relevant to high field studies was determined by measuring the Hall mobility at a magnetic field of 9T. The results of high field measurements showed that at atmospheric pressure and x 0.3 by the Gunn effect. The threshold field, FT, was found to increase steadily with x from about 1 kV/cm in In As to close to 9 kV/cm in InP. In the avalanche region, (x < 0.3), increasing pressure and increasing x produced similar changes in both FT and VT if 1 k-bar was set equivalent to 1% increase in phosphorus. In the Gunn region, despite the increasing threshold field, vT measured remained almost constant with composition. By contrast, with increasing pressure FT remained almost constant and vT dropped about 16% in 15 k-bar. The results were simulated by Monte Carlo calculations of the velocity-field characteristics including an ionized impurity scattering corresponding to the low field mobility of the samples used. The parameters used and their variations with x and pressure were discussed. Reasonable agreement was obtained for the magnitudes of FT and VT and for their variations with pressure and composition. By reducing the impurity scattering to zero, estimates for the characteristics of the pure alloys were obtained. These indicated that vT increases from about 2.6 x 1017cm/s in InP to 3.05 cm/s in In As0.7 P0.3, suggesting this may be a useful material for microwave devices. Analysis of the transition from impact ionization to Gunn effect gave values of the sub-band gap, DeltaETL, of 0.71 and 0.79 eV for In AS0.7 P0.3 and In As0.79 P0.21 respectively. Electron loss to impurity levels normally above the Upsilon1c minimum was observed. The pressure coefficients of the levels are discussed and their energies are determined. A semiconductor-semimetal phase transition, which occurs at 60 k-bar in In As, is found to vary linearly to 100 k-bar in InP and is compared with the theory of Van Vechten.