The photoelectronic properties of CdTe films sintered with various amounts of $CdCl_2$ and $CuCl_2$ have been investigated by the measurements of dark electrical resistivity, photoconductivity, thermoelectric power, optical transmission and by observation of microstructures.
The grain size increases and the porosity decreases, which increases the value of optical transmission, with increasing amount of $CdCl_2$ indicating that the $CdCl_2$ acts as a sintering aid.
For the sintered CdTe films that contained 1 wt% of $CdCl_2$ before sintering, the electrical resistivity decreases sharply with increasing sintering temperature, whereas the resistivity is almost independent of the sintering temperature for the sintered CdTe films that contained 5 wt% or 10 wt% of $CdCl_2$ before sintering. This fact combined with the observed microstructures and the optical transmission data indicates the presence of more than 5 wt% of $CdCl_2$ is necessary to cause liquid phase sintering in the CdTe films. For the specimens which contained various amounts of $CdCl_2$ before sintering and were sintered at a high temperature (such as at 700℃), the microstructures are improved and the electrical resisitivity increases with the increase of $CdCl_2$. Therefore, it can be concluded that the $CdCl_2$ acts not only as a sintering aid but also as a dopant source of donor (Cl) during the sintering of CdTe films.
The dark resisitivity of the sintered CdTe films could be reduced further by a post heat treatment which removes residual $CdCl_2$ in the cdTe films.
From the analysis of the temperature dependence of dark conductivity and C-V characteristics it can also be concluded that the hole concentration is less than $1E15cm^{-3}$ and all the grains are depleted of carrier by the trapping centers at grain boundaries. The electrical resistivity decreases and photoconductivity gain ($A-cm^2/W$) increases with increasing amount of $CuCl_2$ up to 250 ppm due to Cu-doping during sintering.
