DETERMINATION OF THE ELECTRICAL-PROPERTIES OF SEMI-INSULATING GAAS - ROLE OF THE MAGNETIC-FIELD DEPENDENCES OF SINGLE-CARRIER PARAMETERS

The electrical properties of four semi-insulating GaAs : Cr crystals in the temperature range 295-430 K have been determined by using the mixed conductivity analysis, taking into account the magnetic field dependences of single-carrier conductivities and Hall coefficients. It is shown that when the field dependence of the electron single-carrier Hall coefficient is neglected, a very large error in the determination of the hole mobility and carrer concentrations may arise. The intrinsic concentration at various temperatures is calculated from the experimental data and its value at 296 K is n i≈ (2.4±0.3) ×106 cm-3, which compares within a factor of about 1.6 with theoretical values deduced from the band gap and effective masses. The temperature dependences of electron and hole Hall mobilities are found to be rnμn∼T -(0.5-1) and rpμp∼T-2.5, respectively. The determined electron-to-hole concentration ratios for individual samples are in the range 0.01-0.3 which corresponds to the Fermi level lying within ±0.03 eV from the middle of the band gap.