Investigation on the two-step passivation process for CdZnTe detectors

Abstract

ABSTRACT In this paper, the composition, morphology and electrical properties of the passivation layer for CdZnTe detectors were investigated. A two-step passivation was performed under different conditions, including passivation time, temperature and NH 4 F/H 2 O 2 concentration. The obtained passivation layers were characterized by XRD, SEM, XRF and I-V methods. The results showed that the best passivation condition was with the NH 4 F/H 2 O 2 concentration of 10wt%, passivation time of 40min and temperature of 20oC. Under this condition, the passivation layer was purely oxidized and compact, and the surface leakage current of CZT crystals was most effectively reduced. Keywords: CdZnTe, passivation process, surface treatment 1. INTRODUCTION The Cadmium zinc telluride (CZT) had shown great promise as a material for large-volume room-temperature X-ray and gamma-ray spectrometers because of its wide band-gap and high absorption coefficients [1-3]. However, the performance of CZT X-ray and gamma-ray spectrometers was of ten limited by its surface l eakage currents which was a critical factor determining the noise and an alysis efficiency of the detectors. Th us, reducing the surface leakage currents and the noise effects was very important for the fabrication of CdZnTe detectors. It was well known that the surface processing, such as polishing, etching and passivation, had great effects on the surface leakage currents of CZT wafers[4-6]. Usually, the 2–5% Br–MeOH (BM) solution was used to re move the surface damaged laye r introduced by cutting and mechanical polishing to obtain a clean su rface before electrode deposition, which would in return produce Te enriched surfaces[7]. The enrichment of Te on the surface was favorable for Ohmic contacts, but also leaded to great surface leakage. The passivation treatment was an important step in the production of CdZnTe detectors, in order to reduce the surface leakage. The passivation was classified to wet chemi cal methods and dry methods [5,6], with the wet chemical methods more popular, which produced sulfide or oxide films on the CdZnTe surface to restrict the surface leakage currents [8-10]. In this paper, a two-step passivation of the CZT detector was investigated under different conditions including passivation time, NH