University of Minnesota
School of Physics & Astronomy

Physics and Astronomy Calendar

Wednesday, May 25th 2016
Speaker: Bekele H. Badada, University of Cincinnati
Subject: Probing Electronic Band Structure and Quantum Confined States in Single Semiconductor Nanowire Devices

I will explore electronic band structure of various group III-V semiconductor nanowires using electrical transport and photocurrent spectroscopy on photo-lithographically contacted single nanowire devices. The nanowires were grown by MOCVD technique where the growth was initiated by a 50-100 nm gold catalyst which determines the diameter of the nanowire. Typically these nanowires are 4-6 ┬Ám long. Further, I will introduce a more complex GaAs/AlGaAs core-multishell heterosturucres, quantum well tube (QWT), where a thin GaAs layer was embedded inside a thick AlGaAs shell surrounding a 50 nm diameter GaAs nanowire core. Here I will present the nature of exciton localization in single GaAs/AlGaAs QWT nanowire devices using photocurrent (PC) spectroscopy combined with simultaneous photoluminescence (PL) and photoluminescence excitation (PLE) measurements at 10 K . Excitons confined to GaAs quantum well tubes of 8 nm and 4 nm widths embedded into an AlGaAs barrier are seen to ionize at high bias levels. Spectroscopic signatures of the ground and excited states confined to the QWT seen in PL, PLE, and PC data are consistent with numerical calculations. The demonstration of good electrical contact with the QWTs enables the study of Stark effect shifts in sharp emission lines of excitons localized to quantum dot-like states within the QWT. Atomic resolution cross-sectional TEM measurements and an analysis of the quantum confined Stark effect of these dots provide insights into the nature of the exciton localization in these nanostructures.

Faculty Host: Vlad Pribiag

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