Photoluminescence from Microcrystalline Silicon and Related Materials
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PHOTOLUMINESCENCE FROM MICROCRYSTALLINE SILICON AND RELATED MATERIALS M.RUckschloss, B.Landkammer, O.Ambacher and S.Vepfek*), Institute for Chemistry of Information Recording, Technical University Munich, Lichtenbergstrasse 4, D-8046 Garching/Munich Germany ABSTRACT Intense photoluminescence line silicon prepared in timizing the crystallite the grain boundaries due plasma deposited films.
has been obtained from nanocrystalcompletely dry processing by the opsize and the chemical passivation of to a controlled postoxidation of the
INTRODUCTION Photoluminescence from porous nanocrystalline silicon attracted much attention in the last two years. Following to the original work of Canham [1] and Lehmann and G6sele [2] a large number of papers dealing with various aspects of this subject has been published (e.g. [3] and many references there). The red photoluminescence of freshly etched porous silicon, PS, is associated with the passivation of the surfaces of the nanocrystals by chemisorbed hydrogen. Upon oxidation or annealing it vanishes and recovers again when a thin silicon dioxide layer is formed either by thermal [4,5] or anodic [6,7] oxidation. The PS-photoluminescence resembles some features of hydrogenated amorphous silicon, a-Si:H [8,9], but it differs significantly from that of nanocrystalline silicon, nc-Si, deposited from diluted silane [10] or by chemical transport [11] in a glow discharge. However, photoluminescence similar to that of PS can be obtained from nc-Si if the surfaces of the nanocrystals are passivated by thermally produced Si0 2 [12-14] showing a blue shift of the peak energy with decreasing crystallite size [12]. The interpretation of these results and the mechanism of the photoluminescence are still subject of an intense discussion, partially due to the relative poor control and characterization of the PS material. The aim of the present paper is to prepare in a well controllable manner and by fully dry processing compact, mechanically stable thin films of nc-Si embedded in an SiO2 matrix. Such films may have several promising optoelectronic applications and they could also contribute to the understanding of the origin and mechanism of the photoluminescence. *) Author to whom correspondence should be addressed Mat. Res. Soc. Symp. Proc. Vol. 283. 01993 Materials Research Society
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EXPERIMENTAL AND RESULTS The nc-Si:H films have been prepared by via chemical transport [15] in an apparatus Fig.1, or from silane diluted with hydrogen. tion has been done in an apparatus described controll er Temperature
plasma CVD either which is shown in The latter deposiin [16].
•.. Anode Ichmialtrasprtsubstrate silicon
• +•_.
g
._..I Ion Rotary" Turibo
Ubias
pump
Fig.l: Apparatus for the deposition of nc-Si via chemical transport in a hydrogen glow discharge.
In both cases we used a direct current, DC, excitation with the substrate holder placed within the positive column of the glow discharge. This allows us to control precisely the deposition conditions, such as temperature, composition of the
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