Growth And Characterization Of Ordered Ge/Si Islands On Si Substrate

In this thesis,2D period patterns have been fabricated on Si substrate by holographic lithography and Ge/Si islands are grown on it through ultra-high vaccun chemical vapor deposition(UHV/CVD).The change of the pattern in the substrate with thermal cleaning in ultra high vacuum,and effect of the growth conditions on Ge islands are systematically studied.The difference of the growth of Ge islands on patterned substrate compared to that on flat substrate is showed.Moreover,the effect of thickness of Si space layer on the multilayer Ge/Si islands grown by UHV/CVD is investigated.Holographic lithography consists of exposal and etching.2D period pattern is achieved through once exposal when three lights irradiate on photoresist simultaneously.Pattern is transferred to substrate by ICP etching.Then the patterned substrate is oxidized and wet etched to reduce the roughness produced from ICE The period and depth of pattern are 1.2μm and 110～120nm,respectively.The Ge/Si islands are grown on the patterned substrate by S-K growth model. During desorption of native SiO₂ at high temperature in ulta-high vacuum,the depth of pattern become shallow and ordered Si islands are formed on the edge of mesas. These changes are attributed to the Si monomer diffusion resulting from oxide thermal desorption.The distribution of Ge islands on patterned substrate is affected by temperature significantly.Ge islands prefer to nucleate on ridges of pattern at higher temperature.Some are nucleating on Si islands,so the volume of Si islands become larger.However,Ge islands nucleate random on patterned substrate at lower temperature.Comparing to those on flat substrates,Ge islands are formed later for the releasing of strain through patterned substrate.Multilayer Ge/Si islands of different thickness in Si space layer are grown through UHV/CVD.The Ge islands are characterized by X-ray difffraction(XRD),photoluminescence(PL),Raman and so on.The results of XRD indicate that the interface in multilayer changes to well with the increasing of thickness of Si space layer.In diffraction curves,two series satellite peaks produced from wetting layer and Ge islands each are found.It is easy to form dislocation in thinner Si space layer according to the results of PL.The PL arising from Ge islands in sample whose Si space layer is most thick can persist to 175k.The average Ge content in multilayer is around 0.4 from Raman spectra,showing that the interdiffusion between Ge and Si is enhanced.The results reveal that the strain in multilayer is released more in sample of thinner Si space layer.