Investigation of epitaxial P-p CdTe/Hg0.775Cd0.225Te heterojunctions by capacitance-voltage profiling

Abstract

We investigate the electrical properties of isotype P-p CdTe/Hg0.775Cd0.225Te heterojunctions grown in situ by the metalorganic chemical vapor deposition technique. The capacitance-voltage (C-V) characterization of Schottky barriers (SB) is used to study the apparent majority carrier distribution and the valence band discontinuity. The C-V characteristics of metal insulator semiconductor (MIS) devices were used to determine the interface charge density. A theoretical model suitable for analysis of graded heterojunctions was developed based on the numerical solution of Poisson’s equation. The model includes an approximate description of the conduction band nonparabolicity and carrier degeneracy. We describe the procedures used in crystal growth and device fabrication for both SB and MIS structures. We demonstrated, on the basis of experimental measurements and theoretical analysis, that the valence band discontinuity in the devices studied here was 0.15 ± 0.05 eV and the fixed interface charge density was approximately (3 ± 1) · 1010 cm-2. Also, we observed a dependence of the C-V measurements on temperature which seems to be caused by either interface traps or carrier inversion at the CdTe/HgCdTe interface.