Photovoltaic properties of CdTe p-n junctions produced by ion implantation

Abstract

A surface region about 0.22 μm thick of cadmium-annealed undoped n-type CdTe single crystal was converted to p type by implantation of 60-keV As+ ions followed by a cadmium annealing. The electrical properties of the p-type layer were measured as well as the photovoltaic properties of the p-n junction formed in this way. For illumination by sunlight an open-circuit voltage of 0.84 V was found in a cell with a solar efficiency of 3.0%. The parameters of the junction were determined using a model designed to describe the spectral response of the cell.

Insights into post-growth doping and proposals for CdTe:In photovoltaic devices

“…For these samples, the initial decay in the PL intensity in the first one or two nanoseconds is dominated by the fast component τ 1 (0.21-0.54 ns) while thereafter the curve shape matches that for the slower, bulk recombination, lifetime, τ 2 , which falls in the range 1.5-2.5 ns. As expected, these values for polycrystalline material are all somewhat less than those reported for single crystal n-CdTe (5-20 ns) [37][38][39][40].…”

“…(b) Contacting [34]: low resistance contacts to single crystal n-CdTe may be formed with indium, providing the surface is oxide-free and the indium is thick enough, for example, 500 nm. (c) Minority carrier lifetime and diffusion length: A range of values have been reported for τ h in single crystal samples as follows: single crystal Bridgman-0.5 ns [37]; ion implanted single crystal-5.5 ns [38]; epitaxial MBE [39] and single crystal solvent evaporated 18.6 ns [39]. For polycrystalline CdTe grown under excess Te, the lifetime was measured as 7 ns [40].…”

Ion implantation of CdTe single crystals

“…The p-n junction formation was supported by U-I characteristics which show forward resistance of 30 Ω and reverse breakdown of 40V. Chu [7] implanted n-type undopted CdTe by As + ions with energy 60 keV, and dose 10 15 . Electrical and photovoltaic properties were measured.…”

“…Platelets were mechanically polished and chemically etched with a solution of bromine in methanol . The preimplantation annealing of Te rich CdTe in Cd vapour was used for 36 h at 500 o C ensuring Cd overpressure of 0.5 Torr [7]. The implantation with As + at room temperature is not efficient while the damage of structure is so great that the sample becomes semi insulating .…”

Photoreflectance Study of Boron Ion-Implanted (100) Cadmium Telluride

“…Ion implantation I has been successfully used to fabricate both p-and n-type CdTe 2 -5 and to produce controlled amounts of doping in the closeiy related and important semiconductor alloy Hg 1 lCdxTe. 6 , 7 Electro-optic oevices such as infrared detectors 8 and solar cells 9 We have used PR at 77 K to study (100) CdTe implanted with boron both before and after the annealing process. The heavily damaged zone and regions that are partially or fully recovered due to annealing can be identified using their spectroscopic signatures.…”