The continued scaling of Si metal oxide semiconductor field effect transistor (MOSFET) devices to enhance performance is reaching its fundamental limits and the need for new device architecture and/or new materials is driving research and development within the semiconductor industry. Germanium, with its much higher intrinsic carrier mobilities, has a considerable advantage over Si as a channel material and its compatibility with current complementary metal oxide semiconductor (CMOS) technology makes it a very promising candidate. There is currently significant technological interest in the epitaxial growth of high quality relaxed Ge layers directly on Si substrates for potential applications including: high-mobility metal-oxide-semiconductor field-effect-transistors (MOSFETs), infrared photodetectors, solar cells and III-V integration. The crystallographic orientation of the substrate also influences the inversion layer mobility in transistors; compared to (100) orientation, Ge grown on (111) and (110) substrates can considerably enhance the carrier mobilities for electrons and holes. The 4.2% mismatch between Ge and Si is, however, a major drawback for the growth of high quality epitaxial layers, as 3-dimensional islanding, surface roughening and the generation of a high density of defects can occur which are all detrimental to performance of prospective devices. In particular, epitaxial growth on (110) and (111) surfaces is more susceptible to the formation of extended stacking faults as the gliding sequence of the dissociated 30° and 90° partial dislocations is reversed with respect to that for the (100) surface. This means that the concept of a thick graded buffer for gradual strain relaxation is not as easily applicable in the case of (111) and (110) substrates. In this work, we have investigated the growth of relaxed Ge films on (111) and (110) Si substrates by reduced-pressure chemical vapour deposition (RP-CVD) in an ASM Epsilon 2000 reactor using the high temperature/ low temperature growth technique, which comprises of a thin low temperature (LT) Ge seed, a thick high temperature (HT) Ge layer and subsequent in-situ high temperature H2 anneal. We will show how the growth conditions influence both the presence and nature of defects within the Ge layers, their surface morphology and also the state of relaxation using transmission electron microscopy (TEM), atomic force microscopy (AFM) and X-ray diffraction (XRD) techniques. Formation of islands in the 10 nm Ge seed layer has led to a significant enhancement in the quality of the buffer by providing a effective way to relax the layers, reducing the densities of stacking faults and threading dislocations by at least a decade compared to previous studies and also producing a smooth surface around 2 nm rms.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:560390 |
| Date | January 2012 |
| Creators | Nguyen, Van H. |
| Publisher | University of Warwick |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://wrap.warwick.ac.uk/50222/ |
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