INTRODUCTION Reactive ion etching (RIE) for the formation of n- on-p junctions in HgCdTe is a promising alternative to current junction-formation technologies based on ion implantation. Using an H 2 /CH 4 chemistry, RIE has been shown to produce diodes with high per- formance, yield, and uniformity as well as providing a simplified process flow through the use of the pas- sivation layer as a physical mask for the p-to-n con- version process. 1 There are, however, concerns about the long-term stability of junctions formed by a hy- drogen plasma-based process. Attempts to evaluate the stability of RIE-formed junctions in HgCdTe are hindered by the limiting effect of the surface passi- vation on such narrow bandgap materials. This paper examines the effect of two common passivants, ZnS and CdTe, on the vacuum bake-stability per- formance of RIE-formed n-on-p photodiodes in mid- wavelength infrared (MWIR) Hg 1-x Cd x Te (x  0.3). EXPERIMENTAL Using midwave (x  0.3) liquid phase epitaxy (LPE)-grown HgCdTe on CdZnTe, vacancy-doped (1  10 16 cm -3 ) p-type material purchased from Fermionics Corporation (Simi Valley, California), n-on-p photodiodes were fabricated using a previ- ously published RIE process for p-to-n type conver- sion. 1 A schematic diagram of the device cross sec- tion is given in Fig. 1. Prior to passivant deposition, the epitaxial layer was cleaned using organic sol- vents and briefly etched in Br/methanol. In all cases, the passivation was deposited using a thermal-evap- oration process, with the resulting layer used as a physical mask for RIE p-to-n type conversion. Fol- lowing diode formation, both n and p contacts were made using Cr/Au in a lift-off process. Despite the use of Cr/Au for the p contacts, an ohmic contact was achieved by the use of very large contact areas (3 mm 2 ). Because of the bonding technology employed, it was necessary to use large bond pads for the n contacts, in the order of 300 m 2  300 m 2 . The current-voltage (I-V) and capacitance-voltage (C-V) measurements, using a Agilent, (Pala Alto, CA) HP4156 semiconductor parameter analyzer and a HP4280 1 MHz C-V profiler, respectively, were per- formed in a shielded cryogenic vessel with a 0° field of view. All postprocessing baking to assess long- term stability was carried out under vacuum. Journal of ELECTRONIC MATERIALS, Vol. 31, No. 7, 2002 Special Issue Paper Passivation Effects on Reactive-Ion-Etch-Formed n-on-p Junctions in HgCdTe J.K. WHITE, 1,4 J. ANTOSZEWSKI, 1 R. PAL, 2 C.A. MUSCA, 1 J.M. DELL, 1 L. FARAONE, 1 and J. PIOTROWSKI 3 1.—Department of Electrical and Electronic Engineering, The University of Western Australia, WA 6009,Australia. 2.—Solid State Physics Laboratory, Delhi, India. 3.—VIGO Systems,Warsaw, Poland. 4.—E-mail: johnwhite@ieee.org The formation of n-on-p junctions by reactive ion etching (RIE) of HgCdTe using an H 2 /CH 4 plasma has previously been demonstrated to produce high- performance photodiodes. To fully exploit the inherent advantages of this process, a compatible surface-passivation technology that provides long-term stability is required. This paper examines the effects of thermally evaporated CdTe- and ZnS-passivation on RIE-formed photodiodes undergoing low-tem- perature baking in a vacuum at temperatures typically used for Dewar bake- out. Experimental results show that as a single passivation layer, neither CdTe nor ZnS are suitable for vacuum packaging of RIE-formed diodes that are to be operated at cryogenic temperatures. A double passivation layer, how- ever, consisting of CdTe passivation and an insulating overlayer of ZnS, pro- duces photodiodes that are stable throughout 175 h, approximately 1 week, of 80°C baking in a vacuum. Key words: HgCdTe, RIE, CdTe, ZnS, passivation, type conversion, bake stability (Received October 3, 2001; accepted March 25, 2002) 743