A. K. Chowdhury

Effect of temperature on the validity of the einstein relation in heavily doped semiconductors

An analytical expression of the modified form of the Einstein relation in heavily doped semiconductors in which Gaussian band tails are formed near the lower limit of heavy doping is derived for studying the temperature dependence of the diffusivity-mobility ratio of the carriers in such semiconductors. It is found that, with increasing temperature from relatively low values, the ratio first increases in a nonlinear manner and then decreases till, at high temperatures, it approaches its value corresponding to the non-degenerate condition resulting in a peak over a narrow range of temperatures.

Oscillatory effective mass in degenerate narrow-gap semiconductors in a quantizing magnetic field

An attempt is made to study the effect of a quantizing magnetic field on the effective electron mass in degeneraten-type narrow-gap semiconductors at low temperatures. It is found, takingn-Hg1−xCdxTe as an example, that the effective electron mass shows an oscillatory magnetic-field dependence as is expected because of the dependence of the effective mass in degenerate non-parabolic bands on Fermi energy which oscillates with changing magnetic field. The amplitude of oscillations is, however, found to be significantly influenced by the alloy composition whereas the period is found to be independent of the band non-parabolicity, i.e. of the compositional parameter in ternary semiconductors.

Effect of a quantizing magnetic field on the diffusivity-mobility ratio of the carriers in n-channel inversion layers on small gap semiconductors

In the present work, an attempt is made to derive expressions for the diffusivity-mobility ratios of the carriers in n-channel inversion layers on small-gap semiconductors under both weak and strong electric field limits in the presence of a quantizing magnetic field. It is found, taking n-channel layers on p-type InSb as examples, that the ratios show spiky oscillations with charging magnetic field, the periods of oscillations being independent of the degree of band non-parabolicity.

Influence of alloy composition on the dependence of the diffusivity-mobility ratio in ternary semiconductors on a quantizing magnetic field

An expression is derived for the diffusivity-mobility ratio in degenerate narrow-gap ternary semiconductors in the presence of a quantizing magnetic field. With the help of this expression, the diffusivity-mobility ratio is shown, taking n-Hg1−xCdxTe as an example, to have an oscillatory dependence on a quantizing magnetic field. The influence of alloy composition on such dependence is also investigated.

Temperature dependence of the Debye screening length in heavily doped semiconductors having Gaussian band-tails

In the present work, a generalized expression is derived for the Debye screening length of the carriers in heavily doped semiconductors having Gaussian band-tails. The temperature dependence of the screening length is also computed for such semiconductors, taking n-type GaAs as an example.

Effect of a quantizing magnetic field on the capacitance of MOS structures of small-gap semiconductors

An attempt is made to investigate the effect of a quantizing magnetic field on the capacitance of MOS structures of small-gap semiconductors havingn-channel inversion layers under the weak electric-field limit. It is found, takingn-channel InSb as an example, that both the MOS and surface capacitances show spiky oscillations with changing magnetic field. It is further observed that the sharpness and the depths of the spikes increase with increasing magnetic field whereas the depths are found to decrease with increasing thickness of the insulating layer.

Influence of alloy composition on the diffusivity-mobility ratio in n-channel inversion layers on ternary semiconductors

An expression is derived for the diffusivity-mobility ratio of the carriers in n-channel inversion layers on semiconductors like the ternary compounds which have strongly non-parabolic energy bands. The dependence of the ratio on alloy composition is also studied under the weak-field limit taking n-channel Hg1−xCdx.Te as an example.

On the gate-controlled surface capacitance of MOS structures of Si having n-channel inversion layers

An attempt is made to work out a simple theory of gate-controlled MOS capacitance based on the triangular potential-well approximation. The predicted dependence of the capacitance on gate voltage is in excellent qualitative agreement with the recent experimental observation reported elsewhere.