INTERFACE STATES-INDUCED-CHANGE IN THE ENERGY BAND DIAGRAM AND CAPACITANCE–VOLTAGE CHARACTERISTICS OF ISOTYPE <font>ZnTe</font>/<font>CdTe</font> HETEROJUNCTIONS

Abstract

Epitaxial layers of ZnTe have been grown on a (111) oriented CdTe single crystal substrate by thermal evaporation technique at 180°C and a pressure of 10 -6 Torr. X-ray diffraction pattern indicated a highly oriented crystallographic growth of ZnTe (111) layer on CdTe (111) substrate. C–V measurements are carried out at frequencies of 10 kHz and 100 kHz. 1/C 2 versus the forward bias voltage gave a straight line in the voltage range from 1 to 3 V. Extrapolation of 1/C 2 → 0 led to an estimated value of the built-in potential of about 0.58 V. The calculated charge carrier concentration in the lightly doped over-grown layer, ZnTe , has been found to be p = 1.7 × 10 16 cm -3 . It was found that energy band diagram constructed according to the electron affinity model is not the adequate one to explain the capacitance–voltage behavior. Therefore, one should take into account the effect of interface states on the energy band diagram. The interface states density has been estimated to be ~10 13 cm -2 for (111) ZnTe /(111) CdTe heterojunction system. The interface states were identified as hole traps for the ZnTe / CdTe heterojunction. Accordingly, a band bending downward both materials, and a depletion zone in both of them are expected.