Diffusion of iodine into CdTe at room temperature

Abstract

Studies on the diffusion of iodine into CdTe at a temperature of 20°C using four widely differing types of diffusion sources are compared and discussed. The concentration profiles were measured using either a radiotracer sectioning (RTS) technique or secondary ion mass spectrometry (SIMS).The profiles were composed of four parts to which a computer package consisting of the sum of four complementary error functions (erfc) gave accurate fits, providing four empirical values of the diffusivity. The diffusivities for the fastest component in all four cases were in agreement (∼2 × 10−14 cm2 s−1) and were consistent with previously published data. These results indicate that when iodine is diffused from the vapour it is not a suitable long‐termstable dopant in devices where sharp junctions are required.

Electrical activity of iodine-diffused CdTe

“…The other important conclusions that were drawn from these measurements were that the total concentration of iodine at the surface of such slices was 10 23 cm −3 and that the diffusivity of the fastest-diffusing component at room temperature was 10 −14 cm 2 s −1 . 4 These results were confirmed independently by radiotracer sectioning and SIMS and close agreement was obtained 5 between the two measuring techniques.…”

“…3 The projected room temperature diffusivity for the fastest part of the chlorine diffusion profiles (6 × 10 −25 cm 2 s −1 ) 7 was much lower than the corresponding one for iodine. 4 More recently, the diffusion of bromine into CdTe has been studied 8 and the concentration profiles which were measured using SIMS gave four-component profiles, yielding values of diffusivities and activation energies similar to those for the diffusion of iodine into CdTe. 4 The question of the mechanisms involved in the incorporation of iodine into CdTe when iodine was diffused from the vapour led to the measurement of C -V profiles at the Defence Research Agency (DRA), Malvern in both iodine-diffused CdTe slices and CdTe slices that had been diffused with excess vapour of either Cd or Te.…”

“…The levels observed were very much less than the corresponding total concentrations of iodine, but (2) At a diffusion temperature of 500°C (run 1) in a saturated CdI 2 and Cd atmosphere the iodine became electrically active in the regions corresponding to D 3 and D 4 . The conductivity was ntype, as would be expected for iodine on Te sites, and the donor concentration rose to a maximum value of about 10 17 cm −3 before falling along with the total iodine concentration in the tail of the D 4 domain.…”

Analysis of MZO/CdTe photovoltaic device treated with cadmium bromide

“…Previous studies have investigated the effects of bromine, iodine and fluorine as a bulk dopant [6]- [10]. CdBr2 has previously been demonstrated to produce a 5.4 % CdTe solar device [12].…”

Studies on the diffusion of the halogens into CdTe

“…Indium has been the most widely used n-type dopant in CdTe and (Hg x Cd 1−x )Te, but as it has proved to be a fairly fast diffusant [1] attention has been directed to the halogens, which are expected to reside on anion sites and may therefore diffuse at significantly different rates. Iodine has been used on a regular basis as an n-type dopant in epitaxially grown material for infrared devices [2], but recent measurements have shown that iodine is a fairly fast diffusant if diffused from an external vapour source, producing diffusivities of 10 −14 cm 2 s −1 at room temperature [3]. Such measurements have produced complex diffusion profiles which were found to be very closely fitted by a function composed of the sum of four complementary error functions.…”