Low-energy plasma-enhanced chemical vapor deposition for strained Si and Ge heterostructures and devices

We review the potential of low-energy plasma-enhanced chemical vapor deposition (LEPECVD) for the fabrication of strained Si and Ge heterostructures and devices. The technique is shown to be equally applicable to the formation of relaxed SiGe buffer layers, and to entire heterostructures including strained modulation doped channels. Pure Ge channels on Ge-rich linearly graded buffers are shown to exhibit low-temperature hole mobilities up to 120,000 cm 2 V � 1 s � 1 , limited by remote impurity and background impurity scattering rather than interface roughness scattering. Strained-Si modulation-doped field-effect transistors (n-MODFETs) with excellent frequency response have been fabricated by combining LEPECVD and MBE for buffer layer and active layer growth, respectively. Maximum oscillation frequencies of n-MODFETs above 140 GHz have been achieved for active layer stacks both on buffers linearly graded to a Ge fraction of 40% at a rate of 10% per micron, and on constant composition buffers which are 10 times thinner. The use of a thin buffer results in significantly less device self-heating. � 2004 Elsevier Ltd. All rights reserved.