title: Composition homogeneity in InGaAs/GaAs core-shell nanopillars monolithically grown on silicon.
abstract: Alloy composition homogeneity plays an important role in the device performance of III-V heterostructures. In this work, we study the spatial composition uniformity of n-In0.12Ga0.88As/i-In0.2Ga0.8As/p-GaAs core-shell nanopillars monolithically grown on silicon. Cross sections extracted along the axial and radial directions are examined with transmission electron microscopy and energy-dispersive X-ray spectroscopy. Interestingly, indium-deficient segments with width ∼5 nm are observed to develop along the radial ⟨112̅0⟩ directions in the InGaAs layers. We attribute this spontaneous ordering to capillarity effect and difference in group-III adatom diffusion lengths. The slight fluctuation in indium content (∼4%), however, does not induce any noticeable misfit defects in the pure wurtzite-phased crystal. In contrast, the heterostructure exhibits excellent alloy composition uniformity along the axial [0001] direction. Furthermore, abrupt transitions of gallium and indium are seen at the heterointerfaces. These remarkable properties give rise to extraordinary optical performances. Lasing is achieved in the core-shell nanopillars upon optical pump despite the observed alloy composition fluctuation in the radial directions. The results here reveal the potential of the InGaAs-based core-shell heterostructures as efficient optoelectronic devices and high-speed heterojunction transistors directly integrated on silicon.
authors.affiliation: Department of Electrical Engineering and Computer Sciences, University of California at Berkeley , Berkeley, California 94720, United States.
authors.forename: Kar Wei
authors.initials: KW
authors.lastname: Ng
authors.forename: Wai Son
authors.initials: WS
authors.lastname: Ko
authors.forename: Roger
authors.initials: R
authors.lastname: Chen
authors.forename: Fanglu
authors.initials: F
authors.lastname: Lu
authors.forename: Thai-Truong D
authors.initials: TT
authors.lastname: Tran
authors.forename: Kun
authors.initials: K
authors.lastname: Li
authors.forename: Connie J
authors.initials: CJ
authors.lastname: Chang-Hasnain
keywords: III−V nanopillar; alloy ordering; core−shell; laser; nanowire