Cryst. Res. Technol. 46, No. 7, 659 – 663 (2011) / DOI 10.1002/crat.201100106 © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Study of ammonium fluoride passivation time on CdZnTe bulk crystal wafers H. Bensalah* 1 , J. Crocco 1 , V. Carcélen 1 , J. L. Plaza 1 , Q. Zheng 1 , L. Marchini 2 , M. Zanichelli 3 , G. Domínguez 4 , L. Soriano 4 , and E. Diéguez 1 1 Crystal Growth Laboratory, Departamento de Física de Materiales, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain 2 IMEM-CNR, Parma,43100 Italy 3 Department of Physics, University of Parma, Parma, 43100 Italy 4 Departamento de Física Aplicada and Instituto de Ciencias de Materiales Nicolás Cabrera, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain Received 11 March 2011, revised 29 April 2011, accepted 5 May 2011 Published online 20 May 2011 Key words CdZnTe, passivation, XPS, surface leakage current. The chemical etching and the passivation processes of CdZnTe wafers were studied. The treatment effects were tested through an X-Ray Photoelectron Spectroscopy (XPS) analysis and I–V measurement. The chemical etching in 2%Br–MeOH solution may effectively remove the damaged layer and improve the ohmic contact between CdZnTe wafer and Au electrodes making rich the surface with Te. After different etching times, the CdZnTe wafers were passivated with NH 4 F/H 2 O 2 .CdZnTe wafer passivated immediately after etching showed the best passivation efficiency because the enriched Te on the surface was fully oxidized to TeO 2 , which results in the thickest oxide layer, and the most stoichiometric surface. Also the surface leakage current was reduced in comparison with the sample passivated 24 h after etching. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1 Introduction There has been a widespread interest in Cd 0.9 Zn 0.1 Te (CZT) semiconductors in recent years due to its various applications [1]. CZT has been investigated for many potential uses in medical imaging. CZT can also be used in the field of national security, nuclear detecting, nuclear control, astrophysical research and industrial measurement [2,3]. The advantages of the CZT material can be derived from the high average atomic number (Z=50) and density (d = 5.9 g/cm 3 ) yielding CZT detectors that are both efficient and compact. Cd 0.9 Zn 0.1 Te has an energy gap of 1.6 eV and is available in its high resistivity form (10 10 -10 11 Ωcm) as a highly compensated semiconductor where the carrier density is significantly lower than the concentration of deep levels [4]. Surface treatment is a critical and sensitive process in the fabrication of CZT radiation detectors, and plays a critical role in determining the detectors performance. During the process of the CZT detector preparation, mechanical polishing and chemical etching always induce surface damage, dangling bonds, which are considered as the primary factors for high surface leakage current. Furthermore surface leakage can significantly degrade pulse height resolution, rendering a device unusable for γ-ray spectroscopy. In addition, surface properties can influence the surface trap state within the device and can have a significant effect on charge transport and signal formation [5]. The surface passivation of CdZnTe detectors is an important step in the device manufacturing. Therefore, the process of passivation had been typically required to reduce the conductivity of the Te-enriched surface layer and decrease the surface leakage current [3].Various methods have been studied for the CZT surface passivation, which could oxide the surface. Previous studies have shown that hydrogen peroxide (H 2 O 2 ) forms oxides tellurium on the CZT surface, thus acting as a good passivating agent [6]. The KOH aqueous solution leaves a more stoichiometric and smoother CZT surface [7]. In this study we will present results on the use of an ammonium fluoride solution. ____________________ * Corresponding author: e-mail: hakima.bensalah@uam.es