Effects of surface roughness on large-volume CdZnTe nuclear radiation detectors and removal of surface damage by chemical etching

Abstract

This study investigates the effectiveness of chemical etchants to remove surface damage caused by mechanical polishing during the fabrication of Cd 0.9 Zn 0.1 Te (CZT) nuclear radiation detectors. We evaluate different planar CZT devices fabricated from the same CZT crystals. All detectors used electroless Au for the metal contacts. Different polishing particle sizes ranging from 22.1-µm SiC to 0.05-µm alumina were used, which caused different degrees of surface roughness. Current-voltage measurements and detector testing were used to characterize the effects of surface roughness and etching on the material and detector properties.

Surface Passivation Effect on CZT-Metal Contact

“…Wright reported the decrease of the leakage current after NH F H O passivation [6]. However, the leakage current was reported to be increased after immersion in a NH F H O solution from the work by Prettyman and Wright [8], [9]. It was assumed that the NH F H O solution could affect the metal contact; however it was not clearly understood [9].…”

“…Many researchers have shown that NH F H O solution could be one choice for the CZT surface passivation. In the previous work [6], [9], it was reported that the detector performance was enhanced after immersion of the detector into a NH F H O solution. Wright reported the decrease of the leakage current after NH F H O passivation [6].…”

“…However, some researchers reported that the surface resistivity was reduced when the surface was treated with NH F H O [8]. Even Wright reported an increase of the leakage current with a treatment with NH F H O in their later work [9] In the present work, the effect of a surface passivation with NH F H O solution was studied experimentally. The surface passivation with the NH F H O solution could affect the surface between the metal electrodes and the metal-semiconductor contact.…”

“…The I-V curve and the -ray energy spectrum of the detectors were measured and compared to observe the effect of a surface passivation. The leakage current of the detector, which was made with the surface passivation, was 60 nA at bias voltage of 500 V. In the previous work about the passivation effect [9], the leakage current of the detector was reported to be 99 nA in the similar condition.…”

Large area/volume CZT nuclear detectors

“…Reliable surface control is difficult to achieve with simple mechanical polishing; a more reliable method would be to use a chemical process (surface passivation). We have achieved the best performance results from fabricated detectors by applying a chemical treatment in which highly polished crystals were submersed for several minutes in a NH 4 F/H 2 O 2 solution [19].…”