Colloquium: Jos Haverkort – Direct bandgap hexagonal SiGe nanowires.

Lecturer: Prof. Jos Haverkort, Eindhoven University of Technology, The Netherlands

Title: Direct bandgap hexagonal SiGe nanowires.

Abstract:

It has been a holy grail for several decades to observe efficient direct bandgap emission from silicon. Unfortunately, cubic silicon has an indirect bandgap, thus impeding the efficient emission of light. The VLS growth method allows to grow III/V nanowires in either the cubic (zincblende) or hexagonal (wurtzite) crystal phase. This allows to grow hexagonal crystal phase SiGe nanowire shells that feature a direct bandgap in the spectral region between 1.5 and 3.4 µm. This material shows efficient light emission and a subnanosecond radiative recombination lifetime. Moreover, by transferring these nanowires to an AlN substrate, we observe a nonlinear increase of the Fabry-Perot cavity modes, thus providing a clear prove of stimulated emission in hex-SiGe. Our recent research is focused on hex-Ge/SiGe nanoshells which feature type I band alignment. Moreover, the quantum well emission spectra show clear quantum confinement effects. The realization of these quantum heterostructures in hex-SiGe is a first step towards quantum well lasers and hex-SiGe single photon emitters.   

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