[Comparative study on photoluminescence from Ge/PS and Ge/SiO2 thin films].

Ge thin films were deposited on porous silicon substrate using the RF magnetron sputtering technique with Ge target and sputtering for 4, 8 and 12 min respectively. Ge-containing silicon oxide thin films were deposited on n-type Si substrate using the RF magnetron sputtering technique with a Ge-SiO2 composite uarget and with Ge wafer in the target having percentage areas of 5%, 15% and 30%, respectively. These samples were annealed in a N2 atmosphere at 300 degrees C, 600 degrees C and 900 degrees C for 30 min. A comparative study of photoluminescence from Ge/PS and Ge/SiO2 thin films is reported. The FTIR was used to research the structure of Ge/PS thin films. The FTIR showed that the Si-Hx (x = 1-3) absorption peaks disappeared, but Si-O-Si, Si2O-SiH and H2Si-O2 absorption peaks were enhanced, and the surfaces of Ge/PS thin films have formed a goodish integrated cross-linked Si-O-Si network. It was indicated that Ge thin films deposited on porous silicon can improve the level of oxidation. At the same time, the Si-O and Si-Si bonds on the surface of PS thin films were broken, but some new bands such as Si-Ge, Ge-Ge and Ge-O formed. As the results of the experiment showed that the photoluminescence peaks of Ge/PS thin films were located at 517 nm, the sputtering time influenced the intensity of light-emission remarkably and with increasing the thickness of Ge layer coated, the intensity of light-emission dropped abruptly. When Ge sputtered for 12 min, the photolumines cence peak almost disappeared. The photoluminescence peaks of Ge/SiO2 thin films were located at 580 nm, the percentage areas of Ge wafer in the target influenced the intensity of light-emission obviously, and with increasing the percentage area of Ge wafer in the sputtering target, the photoluminescence intensity was reduced greatly. Though with increasing the annealing temperature of different thin films, all the photolu minescence spectra from Ge/PS and Ge/SiO2 thin films changed scarcely, and our explanation is that Ge-related defects at the interfaces between PS and the Ge nanocrystals embedded in the pores were responsible for the photoluminescence of Ge/PS thin films. However, the photoluminescence of Ge/SiO2 thin films' light emission originates from luminescence centers in Si oxide films. Ge/PS and Ge/SiO2 thin films both contained Ge nanocrystals and silicon oxide layer, and have similar structure, however, they have different mechanism behind photoluminescence. The experimental results have been explained reasonably.