Xiaoyan Liang a b, Shize Li a b, Jijun Zhang a b, Chen Xie a b, Liang Yin a b, Yue Shen a b, Linjun Wang a b, Jiahua Min a b
a School of Materials Science and Engineering, Shanghai University, Shanghai, 200444, China
b Zhejiang Institute of Advanced Materials, SHU, Jiashan, 314113, China
## Abstract
Passivation is usually used to reduce the leakage current between contacts of CdZnTe devices with pixel electrodes. For CdZnTe devices with planar electrodes, different passivation sequences and passivation regions result in two different device structures. In this paper, two different passivation sequences were used to treat the etched CdZnTe: depositing electrodes followed by passivation, and passivation followed by depositing electrodes, the difference they caused was whether the region below the contact was passivated. The leakage currents of the two structures were compared, and chemical components and Schottky barriers produced by these two different treatments were measured and discussed. Finally, the energy spectra of the two treatments were tested. It was found that, for CZT devices with planar electrodes, the method of depositing electrodes after passivation could significantly reduce the leakage current, although the contacts and CZT were separated by the passivation layer, however, the lower noise from reduced leakage current improved the energy resolution.
## Introduction
The use of semiconductors to detect X/γ rays has gradually become a trend, CdZnTe is a typical and potential semiconductor, the devices based on CZT have been widely used in medical, security, aerospace, environmental monitoring, and other fields [1,2].
Leakage current is an important factor limiting the energy resolution of CZT. Surface treatment to crystal is an important step affecting leakage current in the process of device preparation [[3], [4], [5], [6], [7]].
Generally, the first step is to mechanically polish the cut crystal. The second step is to use the solution containing Br to remove the scratches and other mechanical damage. However, when CZT is manufactured as a unipolar device with pixelated electrodes (as shown in Fig. 1), the low-resistance Te-rich layer between adjacent electrodes is formed by the second step resulting in a significant increase in leakage current [4]. Eventually, passivation is needed to “neutralize” the low-resistance region between the electrodes. The effect of passivation on the pixel-electrode structure is well understood, but when a planar electrode structure is used, since there is only one contact on the same side, the meaning of passivation becomes ambiguous.
In previous research, different institutions have different treatment methods for planar electrode structures and come to different conclusions. Typically, it can be divided into passivation followed by depositing electrodes [5] and depositing electrodes followed by passivation [6,7]. Fig. 2 shows the two structures produced by the two surface treatments. Obviously, in actual application, the photocurrent will pass through the passivation layer in Fig. 2(a), which is different from that in Fig. 2(b). For the passivation layer in Fig. 2(b), in the previous simulation work [8], we thought it was to improve the low resistance layer on the side face that might cause leakage current, but it still needs to be verified by experiment. In summary, for pixel electrodes and strip electrodes, the meaning of passivation is easy to understand, but when using MSM planar electrode structure, the electrodes are distributed at both ends of CZT, the necessity of passivation and the correct sequence of treatment deserves detailed discussion.
In this work, two different passivation modes were used for the same samples, namely passivation followed by electrodes deposition and electrodes deposition followed by passivation, and their I–V characteristics were compared, XPS was used to compare the two methods of surface treatment, and their Schottky barrier was compared by variable temperature I–V method. Finally, we tested the energy resolution spectrum of the samples to evaluate the practical performance of the two treatments.
CdZnTe Association (CdZnTe.com)
https://www.cdznte.com/thesis/effect-of-passivation-sequence-on-the-performance-of-planar-cdznte-detectors.html