The direct current-voltage characteristic of glass-ITO-n-CdS-p-CdTe-graphite structure is shown in Fig.1 This dependence can be described as

I= I01 exp(eV/AikT) + I02 exp(eV/A2kT) (1)

Fig.1 The forward current-voltage characteristics at different temperatures: 1-193 K, 2-223 K, 3-243 K, 4-273 K, 5-293 K

where A1 = 2 at low voltages of kT/e < V < 0.1 -0.4 V and A2 = 1.0 — 1.5 at 0.1-0.4 < V < VD. While I0 reduces with decreasing of temperature. So, expression (1) can be written as

I = b1(T)exp(S1V) + I02(T)exp(S2V) (2)

The dependence of the direct current on temperature at different voltages is shown in Fig.2. It is seen that the slope of this dependence dI/dT does not depend on voltage.

Fig.1 and 2 allow us to conclude that the predominant mechanism of the direct current is the tunneling of carriers and can be described by the following empirical equation

I = bexp(aT + bV)

where, a and b are experimentally determined parameters which are typical for tunneling — recombination mechanism in heterostructures.

The reverse current-voltage characteristics at different temperatures are presented in Fig.3 and can be described as

Ir — V n (4)

Where n = 1.5 for kT/e < V < 0.8 — 1.0 V and n > 3.0 for 1.0 < V < 10.0 V. For low voltages value of n indicates on thermal generation of carriers in the space charge region. The reverse current mechanism is tunneling at high voltages.

Acknowledgement

The authors would like to thank Professor Y. Goswami and Dr. S.Vijayaraghavan for their support.