X-Ray CdZnTe Detector in Transverse and Longitudinal Photoconductivity Mode

Abstract

The work considers “transverse” and “longitudinal” photoconductivity modes, regarding the direction of radiation, photoconductivity in semiconductor detectors of CdZnTe. Mathematical calculations were made from the representation of the internal area of the detector in the form of radiation absorption sites. The results of the calculations are compared with experimentally measured photocurrent of the detector with a cross section of 2 × 2 mm CdZnTe from the direction of its radiation by X-ray. From the ratio of photocurrents in the range of X-ray radiation energies 35–72 keV for these two cases, a linear coefficient of X-ray absorption by the CdZnTe detector is determined.

APPENDIX

The total carrier (electron) current is a combination of drift and diffusion currents [4]:

$${{j}_{x}} = {{j}_{{{\text{drift}}}}} + {{j}_{{{\text{diff}}}}} = q{{\mu }_{n}}{{N}_{x}}E + q{{\mu }_{n}}(kT{\text{/}}q)d{{N}_{x}}{\text{/}}dx,$$

(A1)

where kT/q is the thermal potential, which is equal to 0.026 V at room temperature. Inserting (4) into (A1), we obtain

$${{j}_{x}} = q{{\mu }_{n}}{{N}_{0}}\exp ( - \mu x)[E - \mu (kT{\text{/}}q)].$$

(A2)

The diffusion current is neglected due to its smallness in the case

$$E \gg \mu (kT{\text{/}}q).$$

(A3)

Neglecting the “dead layer” [7] E = V/L, we find

$$V \gg 0.026\mu L.$$

(A4)

It follows from Table 1 that μL $\leqslant$ 3. Therefore, the diffusion current may be neglected if the applied bias voltage is

$$V \gg 0.078\,\,{\text{V}}.$$

(A5)

The bias voltages used in [1] were 200 and 400 V.