Photoluminescence studies of CdS films grown by close-spaced vapor transport hot walls

Semiconducting films of CdS grown by a modified close-spaced vapor transpor t hot-wall technique were studied by photoluminescence (PL) in the range of 10-300 K. The films were grown with an Ar pressure of 100 mTorr, the subst rate temperature (T-su) varied between 500 and 700 degrees C, while the sou rce temperature (T-so) was kept at 750 degrees C. With these parameters it was possible to obtain different mean grain sizes. Several luminescence ban ds were observed, one located near the band-gap energy around 2.5 eV at 10 K. This band shows a strong temperature dependence and has an excitonic ori gin. Two other bands were detected around 2.4 and 2.1 eV at 10 K, and are d enoted in the literature as green and yellow emission bands, respectively. The lower energy band with a mean width of 150 meV is accompanied by the co rresponding optical phonon replica separated by exactly the LO-phonon energ y of 38 meV at low temperatures. The nature of these bands and the photolum inescence process as a function of the temperature as well as of the grain size will be analyzed and discussed in this work. (C) 1999 American Institu te of Physics. [S0021-8979(99)03718-4].