STRUCTURAL AND OPTICAL STUDIES IN A-CDTE-O ANNEALED FILMS

Thin films of stable crystalline phases of the Cd-Te-O ternary system were prepared by thermal annealing in an Ar flux of amorphous CdTe:O f ilms. The composition of the annealed films depended on the initial ox ygen content in the film, the temperature and duration of the annealin g process. The annealed films were characterized by means of x-ray dif fraction spectroscopy and by optical absorption spectroscopy. The resu lts show that for low oxygen content in the as grown film and high ann ealing temperature, the CdTe cubic phase is the predominant crystallin e phase in the annealed film. For intermediate oxygen content in the a s grown film, the result obtained after the annealing process is a com posite material consisting in the mixture of both CdTe and CdTeO3 crys tallites. The variation of the annealing temperature produces changes in the size of the crystallites of both crystalline phases. It also ca n change the CdTe to CdTeO3 proportion in the films. For low annealing temperature, the size of the CdTe crystallites in the film is <14 nm, the exciton Bohr diameter in CdTe. The optical characterization of th e CdTe-CdTeO3 composite material shows that this system is very suitab le for the study of optical transitions in the electronic band structu re of CdTe. Furthermore, for the films with the smallest CdTe crystall ites it is possible to observe the effects in the CdTe band structure produced by the reduction in the size of the CdTe crystallites to a di mension comparable to the exciton Bohr diameter. The annealing process in the as grown films with high oxygen content produces films compose d by a mixture of the oxide insulating phases CdTeO3 and CdTe2O5. (C) 1996 American Institute of Physics.