CdTe crystals are promising for their applications in optoelectronic devices, such as solar energy converters, optoelectronic modulators, highly efficient detectors for γ- and X-rays at room temperature.
Usually as-grown undoped CdTe crystals show p-type conductivity. Diffusion and ion implantation of III group elements are commonly used methods for the formation of diode structures. These methods could provide semiconductor doping of high quality, but need high temperature processing. Moreover, the diffusion of impurity on given low depth is difficult. To overcome these disadvantages, we have tested a process of doping p-CdTe with Indium under laser radiation in order to create abrupt In profiles for p-n junctions.
(111) CdTe p-type wafers, grown by the THM method were investigated. Indium was used as a dopant impurity. A thin layer of indium was vapor deposited in vacuum on the Te-side surface of p-CdTe crystal before its irradiation. Samples were irradiated at T=300K with multimode Q-switched ruby laser single pulses with 2x10-8 s duration both in air, and in chamber filled with Ar under 2 atmospheres pressure.
It was shown that the use of laser radiation has the potential for doping and producing shallow p-n junction in CdTe crystals. As opposed to doping during the process of growth the formation of p-n junction under laser doping occurs within short time (2x10-8 s) with predetermined locality both in depth and on the surface of crystals. The doping deposition thickness and procedure of irradiation necessary for creation of shallow p-n junction were optimized. Current-voltage characteristics of p-n junction in CdTe crystals were investigated. These characteristics of the p-n junction show diode properties with reverse current of 35 nA and 1.8 nA at 100V bias for 10 x 10 mm2 and for 3 x 3 mm2 structures respectively.
The mechanisms of shallow p-n junction creation under laser radiation are discussed.