Studies On Doping Properties Of CdTe Thin Films Deposited By CSS Method

Owing to its well optoelectronic properties, one of theâ…¡-â…¥compound semiconductors, CdTe has been an ideal absorber material for high-efficiency, low-cost polycrystalline thin film solar cells. We review the development of CdTe based polycrystalline solar cells, summarize its future application, and an overview is given on study of the diverse doping conditions of the CdTe thin films in this thesis.Two aspects of our work are given in the body of this thesis: (1) The Te-doped CdTe thin films are fabricated by Close-spaced Sublimation (CSS), and the effect of Te-rich on the films' properties has been studied. After annealed in different conditions, the effects of annealing are also discussed. (2) Cu has been doped into CdTe films by ion implantation technique, and then annealed in N₂ atmosphere. The effects of annealing and Cu concentration on Cu-doped CdTe films have been studied.Some main conclusions are obtained through the analysis of the crystal structure, morphology, optical and photoluminescence (PL) properties, as follows: (1) the proper Te-doping can improve the crystal quality of CdTe films and cause the lattice constant increasing. The band gap E_g is slightly decreased, while the acceptor energy level has little change, that is to say, Te-doping has little effect on the optical properties of CdTe films. The annealing treatment can improve the crystal quality once more and change the lattice stress caused by various defects. Te phase is observed after annealed in N₂ atmosphere, while the lattice constants and E_g decrease. (2) The proper Cu-doping can improve the crystal characteristic of CdTe films. The lattice defect and damage caused by ion-implantation can be eliminated by annealing, the lattice constants decrease and the Cu₂Te phase is detected; Cu doping also decrease the transmission for NIR light and optical band gap of CdTe films.