The Crystal Growth And Related Properties Of SiGe Nanocrystal In Si,Ge, SOI Substrates

Low-dimensional SiGe, especially the growth and related physical properties of SiGe nanocrystal, is the present attractively research field which can be used for developing the new-generation single electron devices, the lasers and optoelectronic devices, and offer a solution for Si-based optoelectronic integration. The research on the crystal growth and related properties of the SiGe nanocrystal has significantly realistic meaning, and this thesis is focus on the research of the SiGe nanocrystal. In order to take advantage of SiGe nanocrystal, it is very important to control the size, shape and distribution of the nanostructure.In this thesis, the SiGe nanocrystal were fabricated in Si, Ge and SOI substrates by ion implantation technique. The influence of the conditions of implantation and subsequent anneal process was investigated. The microstructure and the visible photoluminescence of the SiGe nanocrystal were characterized. The stress and strain of the substrates with SiGenanocrystal were discussed.(1) SiGe nanocrystal was fabricated in Si substrate by two-step Ge ions implantation and annealing at1100℃. The nanocrystal has a kind of quantum structure with ordered SiGe atomic arrangement and to be formed during amorphous-crystal transformation. The growth orientation of the nanocrystal is followed by<001>siGe//<001>si and (111)SiGe//(111)si.SiGe nanocrystal growth is affected by the annealing process. On one hand, a dense of SiGe nanocrystal can be obtained after2hours furnace annealing (FA) with size of5-7nm in the recrystallization region with15-20at.%Ge content, where the micro defects, such as stacking faults, micro twin crystal and {311} defects can be found. These nanocrystal and defects can dissolve with increased annealing time. On the other hand, completely coherent SiGe nanocrystal can be obtained after180s rapid thermal annealing (RTA) with size of5-7nm in the recsyratallization region with12-14at.%Ge content, and no defects exist in this region.(2) SiGe nanocrystal was fabricated by two-step Si ion implantation with subsequent RTA pecess in Ge substrate. It has been demonstrated that the precipitation of SiGe nanocrystal is due to the local growth along the set of {311} facet at near-surface, which is derived by the strain energy. The SiGe nanocrystal was only grown in the recrystallization region with more than50at.%Si content. Due to the anti-diffusion effect of transient enhanced diffusion, RTA process at900℃is better to fabricate the SiGe nanocrystal in Ge substrate than800℃(3) Ge ions implanted in SOI with high dose can lead to ion mixing around the interface between top-Si layer and BOX layer. SiGe nucleuses were produced by ion implantation due to the cascading warming and ripening during the subsequent annealing. Ball-shaped SiGe nanocrystal with2-5nm was obtained in BOX layer after annealing. The density of the SiGe nanocrystal is1.96×108/cm2. The HRTEM investigation shows that the SiGe nanocrystal can be obtained in top-Si layer, the distribution is dispersed and the stack faults are induced.The growth orientation is followed by<001>SiGe//<001>Si.(4) SiGe amorphous layer was obtained by two-step Ge ion implantation in SOI and the SiGe nanocrystal were grown on the surface of SOI by island growth mode. Two kinds of SiGe nanocrystals and the "micro-ring" structure were formed on the surface. The dynamic model was established to analyse the formation mechanism. In addition, SiGe nanocrystal with diameter of5-7nm, twin crystal and stacking faults were induced in the recrystallization layer.(5) The recrystallization layer of Si substrate after Ge implantation and annealing process was tensile stressed, while the recrystallization layer of Ge substrate after Si implantation and annealing process was compressed. The stress in Ge substrate relax when increase the annealing temperature. The recrystallization layer of the SOI was alloyed after Si implantation and annealing process due to the viscous liquidity of the BOX layer at high temperature. In SOI, the SiGe alloy layer was compressed while island growth occured on the surface.(6) Visible photoluminescence of the SiGe nanocrystal has been measured, which is attributed to the bound exciton. The location of photoluminescence peaks are affected by the size of SiGe nanocrystal while the intensity was affected by the microstructure of the substrate.In summary, ion implantation combined with thermal annealing is adequate technique process to fabricate SiGe nanocrystal in Si、Ge、SOI substrates. The SiGe nanocrystal shows exciting visible photoluminescence phenomenon at room temperature. All these results are useful in Si-based photoelectron research field.