Azhati Lina a, Haofei Huang a, Keyun Gu a, Hongwei Li a, Zilong Zhang b, Ke Tang a c, Zhuorui Chen a, Haitao Ye d, Linjun Wang a c e, Jian Huang a c e
a School of Materials Science and Engineering, Shanghai University, Shanghai 200444, China
b Research Center for Electronic and Optical Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki, Japan
c Zhejiang Institute of Advanced Materials, SHU, Jiashan 314113, China
d School of Engineering, The University of Leicester, Leicester, LE1 7RH, United Kingdom
e Shanghai Collaborative Innovation Center of Intelligent Sensing Chip Technology, Shanghai, China
## Abstract
ZnTe materials exhibit distinctive characteristics that render them exceptionally suitable for the utilization in circumventing the electrode contact issue for the CdZnTe based devices for photoelectric applications. This work employed the co-sputtering technique to fabricate ZnTe:Cu films, probing the influences of Copper (Cu) sputtering power on the film's structural, morphological, optical, and electrical properties. It is disclosed that the sputtering power of the Cu target leads to a proportional increase in CuxTe compounds within the ZnTe:Cu films. Notably, an increase in the sputtering power of the Cu target is found to enhance the carrier concentration of the film, but not decrease the resistivity. This unnormal arose is due to a substantial reduction in carrier mobility at higher Cu target sputtering powers. The ZnTe:Cu film exhibits relatively lower resistivity when the sputtering power of the Cu target is approximately 3 W. The optimized ZnTe:Cu film as a buffer layer for the electrode is favor of remarkable improving the ohmic contact properties between the electrode and the CdZnTe, exhibiting a low contact resistivity of 0.62 Ω cm2. This work offers a promising approach to ameliorate the contact performance for the CdZnTe devices with high performance and high reliability.
## Introduction
CdZnTe is considered one of the most promising candidate materials for nuclear and photoelectric detection [[1], [2], [3]]. However, in the application of CdZnTe semiconductor devices, achieving good ohmic contact has always been challenging [4,5]. A low resistivity contact buffer layer is widely employed between metal electrodes and CdZnTe to overcome the limitations of ohmic contact characteristics [6]. ZnTe, a type II-VI semiconductor material, has gained more atterntion due to its excellent room-temperature properties, which make it appropriate for a variety of applications including Terahertz (THz) wave detections, light emitting diodes, laser diodes, and solar cells [[6], [7], [8], [9]].Compared to CdTe and CdZnTe materials, highly doped ZnTe with low resistivity is an ideal candidate for acting as a back contact interface layer in the CdTe solar cells and the CdZnTe detectors [[10], [11], [12]]. Generally, the back contact interface layers should have low resistivity. However, since Zn cation has a smaller covalent radius than Te anion, the realization of n-type doping for ZnTe is a challenge [13]. Currently, group I-A, group I–B, and group V-A elements are utilized for the p-type doping in ZnTe. The group I-A and group I–B elements mainly achieve the p-type doping by replacing Zn, while group V-A elements achieve this goal by replacing Te. Recently, the elements like Na, Cu, As, N, Ag and Sb have been developed for the doping of ZnTe [[14], [15], [16], [17], [18], [19]]. Among them, Cu has the most potential in realizing the p-type doping for the ZnTe films due to its abundant reserves, ease of availability, and excellent doping flexibility. The incorporation of Cu into the ZnTe lattice will not cause obvious lattice distortion or other defects since the atomic radius of Cu is similar to that of Zn, which ciontributes to high quality of ZnTe:Cu film. Additionally, when Cu is doped into ZnTe, it may combine with Te to form CuxTe compounds, which is beneficial for improving the conductivity of doped films [13]. Therefore, the Cu doping for ZnTe films has gained considerable interest and is presently a prominent subject of research in the realm of p-type ZnTe [20,21].
Recently, various fabrication techniques, such as co-evaporation [22,23], pulsed laser deposition [17], and sputtering methods [24], have been used to prepare ZnTe:Cu films. Among these, the sputtering method is considered an optimization method due to its advantages of simple equipment, fast film growth rate, and high film quality, which are essential for practical applications [25]. At present, ZnTe ceramic targets with fixed Cu doping concentration are generally used in the preparation of the ZnTe:Cu films by the sputtering method. It is a challenge to adjust the amount of Cu doping in the prepared films. To solve this issue, we employed the co-sputtering technique to precisely control the Cu doping by varying the power parameters of Cu targets.
In this work, we proposed a magnetron co-sputtering method to prepare ZnTe:Cu films and explored the effects of the sputtering power of the Cu target on the microstructure, morphology, optical, and electrical properties of the ZnTe:Cu films in detail. The impact of ZnTe:Cu buffer layer on the ohmic contact characteristics between the CdZnTe films and the electrodes was disclosed. This work presents a facile method to enhance the contact performance of CdZnTe devices, and in trun, improve the detection performance and reliability.
CdZnTe Association (CdZnTe.com)
https://www.cdznte.com/thesis/tailoring-ohmic-contact-of-cdznte-based-device-using-a-znte-cu-film-interlayer.html