High Quality III-V Semiconductors/Si Heterostructures for Photonic Integration and Photovoltaic Applications

Detta är en avhandling från Stockholm : KTH Royal Institute of Technology

Sammanfattning: This thesis deals with one of the promising strategies to monolithically integrate III-V semiconductors with silicon via epitaxial lateral overgrowth (ELOG) technology and is supported by extensive experimental results. The aimed applications are light sources on silicon for electronics-photonics integration and cost effective high efficiency multijunction solar cells.The work focusses on the growth of III-V semiconductors consisting of indium phosphide (InP) and its related alloys on silicon primarily because of the bandgaps that these offer for the aimed applications. For this purpose, we make use of the epitaxial growth technique called hydride vapour phase epitaxy and exploit its near equilibrium operation capability to achieve primarily ELOG of high quality InP as the starting material on patterned InP(seed)/silicon wafer. The InP/InGaAsP layers are grown by metal organic vapour phase epitaxy.Different pattern designs are investigated to achieve high quality InP over a large area of silicon by ELOG to realise lasers. First, nano patterns designed to take advantage of aspect ratio trapping of defects are investigated. Despite substantial defect filtering insufficient growth area is achieved. To achieve a larger area, coalescence from multiple nano openings is used. Shallowly etched InP/InGaAsP based microdisk resonators fabricated on indium phosphide on silicon achieved by this method have shown whispering gallery modes. However, no lasing action is observed partly due to the formation of new defects at the points of coalescence and partly due to leakage losses due to shallow etching. To overcome these limitations, a new design mimicking the futuristic monolithic evanescently coupled laser design supporting an efficient mode coupling and athermal operation is adopted to yield large areas of ELOG InP/Si having good carrier transport and optical properties. Microdisk resonators fabricated from the uniformly obtained InP/InGaAsP structures on the ELOG InP layers have shown very strong spontaneous luminescence close to lasing action. This is observed for the first time in InP/InGaAsP laser structures grown on ELOG InP on silicon.A newly modified ELOG approach called Corrugated ELOG is also developed. Transmission electron microscopy analyses show the formation of abrupt interface between InP and silicon. Electrical measurements have supported the linear Ohmic behaviour of the above junction. This proof of concept can be applied to even other III-V compound solar cells on silicon. This allows only thin layers of expensive III-V semiconductors and cheap silicon as separate subcells for fabricating next generation multijunction solar cells with enhanced efficiencies at low cost. A feasible device structure of such a solar cell is presented. The generic nature of this technique also makes it suitable for integration of III-V light sources with silicon and one such design is proposed. 

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