Optical properties of self-organised SSMBE and GSMBE Ge nanostructures grown on SiGe template layers on Si (118)
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Optical properties of self-organised SSMBE and GSMBE Ge nanostructures grown on SiGe template layers on Si (118) G. Brémond(a), P. Ferrandis (a), A. Souifi(a), A. Ronda(b), I. Berbezier(b) (a) Laboratoire de Physique de la Matière, UMR-CNRS, INSA de Lyon, bat 502, 20 Av. Albert Einstein – F-69621 Villeurbanne CEDEX, France (b) Centre de Recherche sur les Mécanismes de la Croissance Cristalline, CRMC2 – UP-CNRS, Campus de Luminy, case 913, F-13288 Marseille, France
ABSTRACT This work reports on the photoluminescence properties of self-organized fully strained Ge dots fabricated using two different growth techniques: gas source molecular beam epitaxy (GS-MBE) and solid source molecular beam epitaxy (SS-MBE). Variable temperature photoluminescence (PL) measurements were carried out on Si/(n)Ge/SiGe/Si structures (n varying from 1 to 7 monolayers) consisting in double layer structures (Ge(n)/Si1-xGex) deposited on (118) oriented Si substrates. The process used consists in realising in a first step a Si1-xGex template layer with a “self-patterned” morphology. Such patterning, based on periodic morphological modulation of the surface is used to confine and organise the Ge dots in a second deposition step. Similar series of experiments with various growth temperatures, Ge coverage levels and Si1-xGex concentrations (x) were done by both GS-MBE and SSMBE. The PL from the 2D wetting layer in the case of n = 3 ML has been found to be more intense in GS-MBE thanks to the passivating role of the hydrogen atoms. The 2D to 3D growth transition is accompanied by the occurrence of a red-shifted broad PL band (L) attributed to the Ge dots. While broadened luminescence is obtained from dots directly deposited on the Si substrate, a narrower band is obtained from dots deposited on the template layer. Moreover the red-shift of the (L) band observed in the latter case is attributed to higher Ge concentration in the dots. On the other hand, there is no effect of the hydrogen on the formation of the islands which show similar optical and structural properties in both growth techniques. The main difference between GS-MBE and SS-MBE concerns a low energy shift in the PL of the SSMBE Ge dots we interpret as due to size, dispersion and Ge concentration or strain effects
INTRODUCTION These last years, there have been a great number of studies aimed at the realisation of an optical device exploiting the strained SiGe/Si semiconductor system by realising optoelectronic integrated circuits using Si processing techniques [1] . The control of Ge/Si selforganized low dimensional nanostructures becomes very important due to the great potentiality of this semiconductor to form quantum dot nanostructures for theoretical modelling and for technological application in nanoelectronics and optoelectronics. According to this aim, we have realised several Si/Ge/SiGe/Si structures grown by both Gas Source Molecular Beam Epitaxy (GS-MBE) and Solid Source Molecular Beam Epitaxy (SSMBE) on (100) and (118) silicon surfaces with various Ge coverage. These struct
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