Compliant substrate of silicon-on-insulator for lattice-mismatched epitaxial films.

摘要

The concept of compliant substrate is being developed for the growth of thick lattice-mismatched epitaxial films without degradation. By relieving the strain within the substrate, compliant substrate can facilitate high quality lattice-mismatched epitaxial films without generating threading dislocation within the films. In this thesis Silicon-on-Insulator (SOI) is employed as the compliant substrate for the lattice-mismatch epitaxial growth of Si _xGe_1–x and SiC films. The compliance of SOI substrate is both theoretically and experimentally investigated. SOI with a very thin top Si layer has been proved as an excellent compliant substrate for the lattice-mismatched epitaxial growth of Si_1–xGe_x films.; The degree of the compliance of SOI substrate is determined by the structural parameters of SOI, which are the bonding strength of top Si layer with the insulator (SiO₂) layer, the thickness of the top Si layer, and the lattice misfit between epilayer and substrate. Dislocation-free epitaxial films can be obtained on the SOI substrate without the thickness limitation, providing the SOI substrate has a very thin Si layer. By using bond and etching back SOI (BESOI) with a 200Å top Si layer as the compliant substrate, high quality relaxed Si_0.6Ge_0.4 films as thick as 1.0 μm have been achieved. A greater than five order of magnitude reduction in threading dislocation density has been achieved by compliant growth compared to the growth on unmodified Si(100) substrates. No other technique can accommodate this 1.6% lattice mismatch without generating a high density of dislocations. Additionally, for the first time we show that it is not necessary to separate the growth and relaxation processes. The relaxation during growth is governed by the nature of the compliant substrate structure that terminates dislocations at the unique crystalline (Si)-amorphous SiO₂ interface of SOI. Results indicate that utilizing SOI as a compliant substrate can be extended to other lattice-mismatched epitaxial films.; Using thin film of SiC grown on SOI has been proposed as the compliant substrates for the growth of GaN epilayers. Monocrystalline SiC thin films with the c-axis aligned with SOI(111) has been achieved. Meanwhile, molecular beam epitaxy growth of GaN by using ammonia as the nitrogen source was developed. High quality GaN have been achieved both electrically and optically. The GaN growth rate of the ammonia MBE can be reached as high as more than 1 μm/hr, which is very promising for the industry application. In addition, p-type Mg-doped GaN grown by ammonia MBE has been achieved for the first time. All these results indicate that our GaN MBE growth method and the resulted materials have great potentials in future device applications.