Graphite/CdMnTe Schottky diodes and their electrical characteristics

The first Schottky diodes based on n-CdMnTe crystals with pronounced rectifying properties are investigated. It is shown that the I–V characteristics of the diodes fabricated by printing colloidal graphite can be described by the Sah–Noyce–Shockley theory of generation–recombination in the space charge region. Exponential increase of forward current with voltage is limited by a relatively low barrier height at the graphite/CdMnTe contact (∼ 0.4 eV) and a significant series resistance of the crystal bulk (∼ 10⁶ Ω at room temperature). Tunneling due to high concentration of uncompensated impurities in investigated Cd_0.9Mn_0.1Te crystals (7 × 10¹⁷ cm⁻³) does not allow increasing the reverse bias voltage to the values needed for the operation of x- and γ-ray detectors. High concentration of uncompensated donors is interpreted by the fact that a certain part of the Mn atoms does not substitute for Cd but plays a role of over-stoichiometric impurities. In the case of the presence of a thin intermediate insulator layer in the graphite/CdMnTe contact, a rapid increase in the current for both polarities of high voltage due to the Frenkel–Poole emission is observed. The obtained results shed light on the problems of technology of growing and post-processing CdMnTe crystals regarded as a prospective material for x- and γ-ray detectors. (paper)