Surface processing of CdTe crystals by an excimer laser and its application in fabricating nuclear radiation detectors

Abstract

PACS 85.40.Ry Excimer laser based surface processing of CdTe crystals is investigated in two different ways, namely laser ablation and laser enhanced impurity doping, for their applications in fabrication of nuclear radiation detectors. Micro-pattering on CdTe surface is performed by irradiating the laser through a shadow mask placed on the CdTe in a high vacuum condition. On the other hand, single pulse laser irradiation on the thin In-layer evaporated CdTe surface at a high-pressure argon gas environment produced an In-doped ntype thin surface layer. Finally, a strip type CdTe nuclear imaging detector was constructed by utilizing these two distinct features of excimer laser.1 Introduction Excimer laser processing of semiconductors has been investigated since the past several years. This technique has an advantage that extremely high temperature can be achieved at the semiconductor surface without affecting the bulk because of the high absorption coefficient of excimer laser in semiconductor materials [1,2]. This is of particular interests for those semiconductors, like CdTe, which are vulnerable to high temperature processing [3,4]. This useful feature of excimer laser makes surface processing of semiconductors possible in two different ways. First, a variety of structures or desired etched patterns on the semiconductor surface can be formed by laser ablation by irradiating laser through a contact type masks or non-contact projection type masks in a high vacuum condition. Second, impurity doping on a thin semiconductor surface can be achieved by the laser enhanced impurity diffusion technique. For this the laser is irradiated on the dopant deposited semiconductor surface placed in a high pressure inert gas environment. Irradiation at a high gas pressure condition helps to suppress the ablation effect of the laser, and thus assists the impurity incorporation into the molten semiconductor surface.We have been studying the application of excimer laser processing to the II-VI compound semiconductors by strictly controlling the laser parameters and other irradiation conditions, like ambient gas and pressure, etc. We have previously reported on laser-assisted n-and p-type doping of CdTe [5,6] and ptype doping of ZnSe [7]. Here we present the results based on excimer laser ablation and impurity doping in CdTe crystals, and an application of these techniques on the fabrication of a monolithic nuclear imaging detector.

Optical emission characteristics of ablation plasma plumes during the laser-etching process of CdTe

“…1 It has been reported that laser processes for CdTe such as crystal growth and impurity doping were performed. [5][6][7][8] Low energy density laser irradiation was used in these laser processes. 7,8 This suggests that KrF excimer laser irradiation enables highspeed etching of CdTe.…”