Optical Properties of Random Multilayers of Amorphous A-Si:H/A-Si 3 N 4+x :H and the Classical Localization
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OPTICAL PROPERTIES OF RANDOM MULTILAYERS OF AMORPHOUS A-Si:H/A-Si 3N4+x:H AND THE CLASSICAL LOCALIZATION Shoji Nitta, Kohji Ogawa, Takehiro Furukawa, Takashi Itoh and Shuichi Nonomura Department of Electronic and Computer Engineering, Gifu University, 1-I Yanaido, Gifu 501-11 Japan ABSTRACT In the optical reflectance spectrum of the random multilayers of a-Si:H/ a-Si3N4+x:H, itis observed an anomalous peak which is explained by the classical localization of light propagation. The following two subjects are discussed in this report; (a). The Kramers-Kronig transformation is done including the anomalous disorder-related reflectance peak. Extra absorption coefficients Aa are obtained by this analysis. Energy dependence of the localization length l(hv) of light propagation are obtained by l(hv)=lI/Aa(hv). (b). The other is the experiment on scaling where the ratio of the disorder and the average layer thickness is kept constant but the size of each layer is changed ineach experiment.
INTRODUCTION Amorphous semiconducting multilayers i.e. amorphous superlattices have been studied extensively in recent years, making periodic amorphous multilayers and studying the properties of these films. We have started recently to study how the disorder introduced to amorphous multilayer films affects to the physical properties [1-4]. By using a computer controlled glow-discharge decomposition apparatus, we have prepared amorphous random multilayer films of a-Si:H/a-Si 3 N4 +x:H and aSi:H/a-Si 0 .6N0.4:H with the random distribution of the well or the barrier layer thickness. Two effects associated with randomness in the distribution of layers were observed in the optical transmittance and reflectance spectra [2]. One isthe distortion of the interference patterns inthe spectra which can be explained by taking into account the multiple reflections and transmissions at each layer. The other isa disorder-related reflection peak which can be understood by the classical localization of light propagation [3-51. In this paper, the following two subjects are discussed. One is the experiments on the scaling where the ratio of the disorder and the average layer thickness is kept constant but the size of each layer is changed ineach sample. The other is the reduction of extra-absorption coefficients Aa by the Kramers-Kronig transformation of reflectance spectra including the anomalous disorder-related reflection peak. Energy dependence of the localization length of light propagation l(hv) are obtained by using l(hv)= lI/Aa(hv).
Mat. Res. Soc. Symp. Proc. Vol. 219. ©1991 Materials Research Society
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EXPERIMENTAL ASPECTS Amorphous semiconducting multilayer films made of hydrogenated amorphous silicon (a-Si:H) as the well layers and amorphous insulator hydrogenated silicon nitride (a-Si3N4+x:H) as the barrier layers, were deposited onto substrates of Coming 7059 glass kept at 250 *Cby using a small size capacitively coupled glow discharge decomposition apparatus. The volume of main reaction chamber was about 200 c.c.. We used a small reactio
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