Optical absorption and luminescence properties of wide-band gap amorphous silicon based alloys F. Giorgis a, * , P. Mandracci a , L. Dal Negro b , C. Mazzoleni b , L. Pavesi b a INFM and Physics Department, Polytechnic of Torino, C.so Duca degli Abruzzi 24, 10129 Torino, Italy b INFM and Physics Department, University of Trento, Via Sommarive 14, 38050 Povo, Italy Abstract Optical measurements of hydrogenated amorphous silicon nitride and silicon carbide alloys are performed and analyzed to correlate the absorption and emission properties. We found that for a-Si 1x N x :H 0 < x < 0:52 and a- Si 1x C x :H 0 < x < 0:5 samples the photoluminescence (PL) spectra and the carrier lifetime distributions depend on the localized tail states as measured by photothermal de¯ection spectroscopy (PDS). These data support the static disorder model. For C-rich alloys 0:5 < x < 1 the radiative properties do not ®t the model predictions due to the presence of C clusters. Ó 2000 Elsevier Science B.V. All rights reserved. 1. Introduction Hydrogenated amorphous silicon nitride and silicon carbide alloys (a-Si 1x N x :H and a- Si 1x C x :H) have been used for a variety of micro- electronic and optoelectronic applications [1]. In fact, these alloys have a tunable optical gap from 1.9 to 5 eV and from 1.9 to 3.6 eV, for a-Si 1x N x :H and a-Si 1x C x :H, respectively, depending on ni- trogen or carbon content [2,3]. In addition, the alloying increases the room temperature radiative eciency by several orders of magnitude and shifts the emission band towards higher energy [4]. These properties render silicon±nitrogen and silicon± carbon alloys useful for light emitting devices. Early studies established some relevant features of the photoluminescence (PL) properties of a- Si 1x N x :H and a-Si 1x C x :H ®lms [4,5]. On the other hand, there is a lack of information about the carrier recombination kinetics and only few anal- ysis of time resolved PL are reported [6,7]. The aim of this work is to analyze both absorption and emission processes in a-Si 1x N x :H and a-Si 1x C x :H samples in a wide compositional range. The optical properties are investigated by transmittance±re- ¯ectance (T±R), photothermal de¯ection spec- troscopy (PDS), stationary and time resolved PL measurements. Such techniques allow us to link the most relevant emission features, such as the PL line-shape and the lifetime distribution, to the electronic density of states (DOS). 2. Experimental The samples were deposited by a 13.56 MHz plasma enhanced chemical vapor deposition (PECVD) system on (1 0 0) Si wafers, 7059 Corn- ing glass or quartz substrates. The a-Si 1x N x :H (a- Si 1x C x :H) ®lms were grown in SiH 4 NH 3 H 2 SiH 4 CH 4 gas mixtures. The other depo- Journal of Non-Crystalline Solids 266±269 (2000) 588±592 www.elsevier.com/locate/jnoncrysol * Corresponding author. Tel.: +39-011 564 7355; fax: +39-011 564 7399. E-mail address: giorgis@polito.it (F. Giorgis). 0022-3093/00/$ - see front matter Ó 2000 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 - 3 0 9 3 ( 9 9 ) 0 0 7 4 8 - 6