Abstract
The high electric field properties of GaAs have been investigated using a uniaxial stress apparatus, developed at the University of Surrey, and the hydrostatic pressure equipment at STL. An initial increase of the Gunn effect threshold field with pressure was observed, in contrast to previous measurements which are explained qualitatively in terms of pressure effects on non-ohmic contacts. Comparison of the results with Monte-Carlo calculations suggests that it may be incorrect to ignore the L1c minima as in previous analyses. Indeed, best agreement is obtained with the L1c valleys at 0.38 eV and the X1c valleys at 0.40 eV above the T1c minimum. Uniaxial stress measurements of low-field resistivity and the threshold field also provide evidence that the L1c and X1c valleys are at approximately the same energy. Deformation potentials of the conduction band have been determined. T1c valley, (Ed °-a) = -7(+/-2) eV; X1c valleys, Eux = 21(+/-9)eV and (Edx-a) = -5(+/-5) eV; L1c valleys, EuL = 22 (+/-3) eV and (EdL-a) = -10(+/-3) eV. High field measurements have also been made on InP and InAs. The InP threshold field results agree with preliminary calculations using a 2-level T-L model. The InAs results extend earlier data into the region where the Gunn effect is the dominant mechanism over avalanche breakdown and the T-L sub-band gap is determined as 0.94(+/-.07)eV. The threshold field is found to increase approximately proportional to the effective mass in the range 33-42 kbar and these results are also compared with Monte-Carlo calculations. Impurity levels have been observed both in the forbidden gap and degenerate with the conduction band. Information on their positions is discussed and their effects on high field behaviour considered.