TABLE OF CONTENTS Most of the early work on binary Si 1 ? xGe x alloy films was performed using MBE whereas growth using CVD systems started much later. Several excellent reviews on SiGe alloy layers have appeared in the literature [1, 82, 83]. In the following, we briefly discuss the development and general characteristics of SiGe films grown using various techniques.
Kasper and Herzog [84] were the first to attempt the growth ofSi 1 ? xGe x on Si at 750 C using MBE. At this high temperature, three-dimensional growth and islanding were observed. Using MBE, the concept of strained layer epitaxy [85] was applied again to Si/SiGe material system by Bean et al. [86] in 1984 at a low temperature (550 C). In the case of strained layer epitaxy, lattice mismatched layers can be grown without misfit dislocations if the thickness is kept below a critical thickness. At this low temperature, it was found that the critical thickness for the epilayer was several times higher than the value that can be obtained from the mechanical equilibrium theory [87]. The key feature of this low temperature technique is that two-dimensional growth of strained Si 1 ? xGe x containing a high concentration of Ge is possible as shown in the atomic force micrograph (figure 2.7).
