Seminar
Nanoscale Type II Semiconductor Heterostructures:
Physics and applications
Prof. Yong Zhang
Electrical and Computer Engineering Department
University of North Carolina-Charlotte, USA
yong.zhang@uncc.edu
时间：6月13日，下午4:00-5:00，教12-201室
Abstract
In most cases we only consider whether or not the material properties of one individual material are suitable for a specific application, for instance the bandgap of a semiconductor is the primary consideration for a solar cell. However, if we include heterostructure of the two materials in the repository of the candidates, the options could be greatly increased. For the photovoltaic application, the conversional wisdom would suggest to find a semiconductor with a bandgap in the range of 1.0 – 1.6 eV for a single junction solar cell, because the Shockley-Queisser detailed balance theory predicts that under one sun a semiconductor with its bandgap in this range can potentially achieve an energy conversion efficiency > 30%. Many semiconductors with larger bandgaps (e.g., ZnO and ZnSe), are usually considered only useful for serving the supporting role such as a transparent electrode. It has recently been predicted that when two large bandgap semiconductors (e.g., ZnO and ZnSe or GaN and GaP), which on their own neither of them would be an efficient light absorber, form a type II heterojunction, it can absorb a much broad spectrum of light due to the interfacial transition, as though the heterojunction has a much lower bandgap than any of the components. Therefore, an array of type II heterojunctions of two large bandgap materials, core-shell nanowires in particular, can potentially make an efficient solar cell. I will talk about the electronic structures of the type II core/shell nanowires from density-functional calculations, the experimental observations of the signatures of the type II nanostructures in optical absorption, photoluminescence (PL), and time-resolved PL, and the demonstration of a prototype solar cell based on a ZnO/ZnSe core/shell nanowire array. The device shows a photo-response threshold of around 1.6 eV, much below the bandgap of either component (3.3 and 2.7 eV, respectively), an open circuit voltage of 0.7 V, among the highest reported values for the nano-structured PV devices.
简介
Prof. Yong Zhang
Electrical and Computer Engineering Department
University of North Carolina-Charlotte, USA
yong.zhang@uncc.edu
Yong Zhang received B.S. and M.S. in Physics from Xiamen University in 1982 and 1985, and Ph.D. in Physics from Dartmouth College in 1994. He was with National Renewable Energy Laboratory (NREL) from 1994-2009, first as a postdoc and later Senior Scientist of the Basic/Material Sciences Center. In 2009, he joined the ECE dept of UNC-Charlotte as Bissell Distinguished Professor. His group’s current research activities include alternative materials and structures for photovoltaics (e.g., ZnO/ZnSe nano-heterostructures), IR detector materials (e.g., InAs/GaSb SLs and MCT), inorganic-organic hybrid materials, graphene, graphene/Si heterostrutures, InGaN and AlGaN LED materials, and some basic solid state research. He has published more than 150 papers and book chapters.
