Si/Ge Intermixing and Island-Island Interaction in Ge/Si(100) Self-Assembled Islands
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Si/Ge Intermixing and Island-Island Interaction in Ge/Si(100) Self-Assembled Islands G. Capellini1), M. De Seta1), and F. Evangelisti 1,2) 1) Istituto Nazionale per la Fisica della Materia e Dipartimento di Fisica Università di Roma Tre, via della Vasca Navale 84, I-00146 Roma, Italy. 2) Istituto di Elettronica dello Stato Solido, IESS-CNR, Via Cineto Romano 42, I-00156 Roma, Italy. ABSTRACT In this paper we present a study of the influence of the growth rate and deposition temperature on the growth dynamic of self-assembled Ge/Si(100) islands. By combining AFM and XPS measurements we show that the main effect of rising the deposition temperature is an enhancement of the Ge-Si intermixing. The actual composition of the Ge islands as a function of deposition temperature has been measured in the 450 °C- 850 °C range: the Ge content x in the alloyed epilayer was found to decrease from x=1 to x=0.28. By changing the growth rate at fixed deposition temperature we were also able to modify the island density. The influence of the island density on the island size has been investigated. We found that an increase of the island density from 109 to 2×1010 cm-2 at T=600 °C brings about a change of the mean island size from 85 to 55 nm. This reduction is explained in terms of island-island interaction effects on the growth dynamic.
INTRODUCTION The strain energy stored during the growth of highly mismatched semiconductor heterostructures is relaxed mainly by the island self-organization [1-4]. The island size, the island size distribution and the island density are strongly dependent on the effective mismatch that exists between the epilayer and the substrate [5]. However the effective misfit can be modified by intermixing [6] and/or by island-island elastic interaction [7]. As a matter of fact, intermixing of the chemical components represents an alternative way for the system to reduce the strain field built up during the growth. Moreover, the elastic interaction between dense islands avoids a complete deformation of the substrate lattice planes, leading to a stiffer substrate. Although intermixing in the Ge-Si system has been reported by several groups [8-15], a quantitative study of its influence on the island growth has not, to our knowledge, been reported. Island-island interaction and its influence on the island evolution has been observed in the SiGe/Si system [16] but no data are available concerning the higher mismatched Ge/Si heterostucture. In this paper we present a systematic investigation of the influence of the deposition temperature and growth rate on the formation dynamics of the Ge/Si(100) islands. The presentation has been divided in two sections. In section A we present a new method, based on a combination of the AFM/XPS techniques, that allowed us to quantify the average composition of nominally pure Ge islands deposited in the 450-850 °C temperature range. In section B we focus on the possibility of tuning the island density by changing the growth rate. It is shown that the growth rate influences the isla
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