Electrical Properties of Te-Doped n-Type InSb At Low Temperatures

Abstract

Measurements of the longitudinal and transverse direct current (de) magnetoresistance of moderately doped n-InSb samples were carried out as a function of (i) temperature, T, down to 18 K and (ii) magnetic field up to 4.8 kG. Three different conduction mechanisms were observed.

The excess donor concentrations of the investigated samples were

9.5 x 1013 cm-3, 1.5 x 1QI4 cm-3 and 1.7 x 1014 cm-3. The average

spacing between the donors was estimated and found to be in the order 0 of the effective Bohr radius of this system (650 A). The present

concentrations, therefore, were assumed to be of a moderate type.

At low temperatures, in absence and presence of weak magnetic fields, the behaviour of the conductivity was of a metallic- like one, i.e., the conductivity cr tends to a finite value as T -7 0 K. However, at high magnetic fields, a metal-insulator transition might occur at a particular threshold value, He. This critical magnetic field depends on the concentration of the carriers. He, indeed, was found to increase as the concentration was increased. The presence of the magnetic field leads to a shrink in the electron wave functions associated with the different donors. The result is that ; at a particular field, He, the overlap of the adjacent wave-functions will be negligibly small so that the donors may become isolated. Hence, metal-insulator transition may occur. High concentrations, then needs high magnetic fields to induce such transition.

Measurements carried out at zero magnetic field in the ionized impurity scattering regime (low temperatures, below 50 K) show that the resistivity p varies with T as p - T-a where a- 0.7. This is less than the expected theoretical findings. This may be due to a possible contribution