The Role of Si-H, Si-H 2 and Oxygen in the Photoluminescence of Porous Si
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The Role of Si-H, Si-H 2 and Oxygen in the Photoluminescence of Porous Si. J.M. Lavine and A.J. Bellezza, Electrical EnEineering Department and S.P. Sawan and Y-T. Shieh, Chemistry Department, University of Massachusetts Lowell, One University Avenue, Lowell MA 01854. ABSTRACT. We have observed no correlation between the presence or absence of the FTIR1 spectral lines at 669 and 2089 cm- 1 (Si-H) and at 912 and 2112 cm- (Si-H 2 ) and the photoluminescent output of porous Si. We have observed no correlation between the presence 1or absence of PL output and the growth-of the Si-O-Si line at 1105 cm- . As a result we suggest that surface passivation plays no role in the PL 1 output. We also suggest that the growth of the Si-O-Si line at 1105 cm- under photo-oxidative conditions results in the alteration of the backbone of a Si-backboned species and not in the attachment of 0 at the surface. Considerable controversy surrounds the role of the surface in the photoluminescence (PL) of porous Si (PS). In his original report of the observation of visible PL from anodized Si, Canham [1] placed strong emphasis upon hydrogen passivation of the surface to support his quantum-wire model of the phenomenon. Tischler et al [2] supported this point of view by observing the presence of the Si-H bond in the FTIR spectra of PS. Tischler et al also observed a large increase of the 1105 cm- 1 Si-O-Si bond after photo-oxidation which resulted in the quenching of the PL output. Recently Tischler et al [3] have directly related the loss of H to the decrease of PL output with photo-oxidation. The premise is that anodic oxidation in HF provides hydrogen passivation of the surface which reduces surface recombination enabling radiative recombination to occur. Photo-oxidation on the other hand, exchanges 0 for H providing non-radiative transitions which quench the PL output. While Tischler and his coworkers have concentrated on the Si-H bond, Tsai et al1 [4] have stated that Si-H 2 which is observed at 912 and 2112 cm- is essential for the observation of PL. Recently Prokes et al [5] have stated that H may play a role more important tl~an that of a passivant. Recently Robinson et al [6] studied the 912 cm-' (Si-H2) line during heating in "high vacuum and could not relate the loss of P'L with the decrease in intensity of this line, in direct contradiction to Tsai et al [4]. Tsai [7] and his coworkers have recently reported the hydrogenation of PS in boiling H20 which resulted in a small blue shift of the PL output. However, they report no FTIR or other data to support the presence of an increased concentration of H. Canham et al [8] have repeated their support of the importance of H on the surface and reported SIMS measurements detecting concentrations of H, C, 0 and F on the surface of their PS samples. They have also reported on the behavior of these elements on the surface of samples stored at room temperature (RT) for protracted periods of time. They have noted a small loss of H for a storage time of one year and a decrease of the 4.20K PL ou
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