Development of contact technology for CdZnTe pixel radiation detectors

The University of Surrey and STFC (RAL) are both leading centres for the development of semiconductor detectors for X-ray imaging and spectroscopy. In this project the student will develop new technologies for CdZnTe pixel detectors, with a particular emphasis on the study of metal-semiconductor contacts and the influence of contact performance on CdZnTe X-ray detectors. CdZnTe pixel detectors are of particular interest for hard X-ray and gamma ray imaging applications, in particular for space science and synchrotron measurements. There is a growing interest also in the COBRA double beta decay project which if selected would need a large development in high performance isotopically pure CdZnTe detectors which would benefit from this project. Both partners are actively developing CdZnTe detectors, for example through characterisation of bulk properties and the charge transport performance in CdZnTe. Both applicants are co-investigators in the RC-UK/EPSRC Basic Technology HEXITEC programme to develop CdZnTe, and have access to a wide range of CdZnTe material produced by the majority of the significant crystal growers worldwide. In order to make practical imaging detectors for STFC instrumentation we need to pattern the bulk material with arrays of electrically active, stable, small feature size electrodes. These have to control the electric field in the devices, extract the signal effectively and be electrically isolated from each other. The student will focus on developing cost effective, high performance contacts that will be stable in the typical STFC scientific environments. Increasingly the bulk properties of CdZnTe continues to improve, and the relationship between charge transport properties and detector performance is becoming better understood. However in contrast the role of metal-semiconductor contacts in CdZnTe radiation detectors is still a major topic of investigation, for example the role of non-uniform barrier height, near surface oxidation, and inter-pixel passivation. The project will therefore concentrate on the development and optimisation of various metal-semiconductor contacts for CdZnTe, which may include electroless metal deposition, and/or ion implantation techniques. The electrical performance of the contacts will be studied, and compared against different types of CdZnTe material supplied by various crystal growers. Pixel detector test structures will be fabricated, suitable for testing with RAL ASICs, and passivation methods will be developed, for example to optimise inter-pixel resistivity.