Influence of phosphorus ion implantation on the optical properties of CdTe bulk crystal

Bulk CdTe crystals were implanted with 400 keV phosphorus ions to investigate the dopability of the host material. Induced devastation in crystal structure related to changes in optical constants of the material was examined by UV–Vis-IR transmittance measurements and spectrometric ellipsometry in a wide range of energies, corresponding to 200–2500 nm for transmittance and 191–2000 nm for ellipsometry. We used phosphorus particle fluences in a range of 5⋅1013 to 5⋅1016 P/cm2. Such fluences should provide p-type dopants concentration at a range of 1018 to 1021 P/cm3 assuming an average range of implanted ions (R) and longitudinal straggling (SR) as R ± SR = 403 ± 166 nm as estimated by SRIM software. The highest doping level was achieved with minor damages in the host lattice. Charged phosphorus particles implanted into bulk CdTe produce sublayer of CdTe:P, indicated by changes in the optical constants and luminescence. It was also observed that the doped layer of CdTe:P affects the transmittance of the crystals. Room temperature micro-Raman spectra of implanted samples, obtained with 532 nm and 785 nm lasers, do not differ from those for an undoped CdTe crystal. Luminescence measurements performed at temperature range down to 11 K show great improvement in luminescence emission, strong band-acceptor excitonic emission (A,X), exciton binding energy EXB = 8.7 meV and shallow acceptor level established by P-ion at about 19.1 meV above valence band maximum (VBM). We concluded that bulk crystals can be successfully doped with phosphorus ion of 400 keV energy up to ion fluences at the range of 5∙1016 P/cm2.