Electron energy structure of self-assembled In(Ga)As nanostructures probed by capacitance-voltage spectroscopy and one-d
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Christian Notthoff, Matthias Offer, Cedrik Meier, and Axel Lorke Department of Physics and CeNIDE, Universita¨t Duisburg-Essen, D-47048 Duisburg, Germany
Chennupati Jagadish Department of Electronic Materials Engineering, Research School of Physical Sciences and Engineering, The Australian National University, Canberra ACT 0200, Australia
Andreas D. Wieck Solid State Physics, Ruhr-Universita¨t Bochum, D-44780 Bochum, Germany (Received 29 September 2008; accepted 5 December 2008)
The electron energy structure of self-assembled In(Ga)As/GaAs nanostructures, quantum dots, and quantum rings was studied with capacitance-voltage spectroscopy and one-dimensional numerical simulation using Poisson/Schro¨dinger equations. The electron energy levels in the quantum dots and quantum rings with respect to the electron ground state of the wetting layer were determined directly from capacitance-voltage measurements with a linear lever arm approximation. In the regime where the linear lever arm approximation was not valid anymore (after the charging of the wetting layer), the energy difference between the electron ground state of the wetting layer and the GaAs conduction band edge was obtained indirectly from a numerical simulation of the conduction band under different gate voltages, which led to the erection of complete electron energy levels of the nanostructures in the conduction band.
I. INTRODUCTION
Recently, much attention has been devoted to investigating self-assembled nanostructures, such as quantum dots (QDs) and quantum rings (QRs), due to their great potential in device applications.1,2 To further improve device performance, it is important to know the energy structure of these nanostructures. Much work has been done to resolve the electronic structure of these nanostructures theoretically.3–8 Experimentally, the electronic structure of these nanostructures can be assessed by optical and transport measurements. Some experimental work has also been done to understand the electronic structure of QDs and QRs by using photoluminescence and photoluminescence excitation spectroscopy, photoa)
Address all correspondence to this author. e-mail: [email protected] This paper was selected as an Outstanding Symposium Paper for the 2008 International Materials Research Conference, Symposium D. To maintain JMR’s rigorous, unbiased peer review standards, the JMR Principal Editor and reviewers were not made aware of the paper’s designation as Outstanding Symposium Paper. DOI: 10.1557/JMR.2009.0293 J. Mater. Res., Vol. 24, No. 7, Jul 2009
current spectroscopy, capacitance-voltage (C-V) spectroscopy, and absorption spectroscopy, among other methods.2,9–17 As for the use of C-V spectroscopy to determine absolute energy scales, one problem is to determine the Schottky barrier formed on the sample surface. There are two possible ways to do it: one way is to use a reference sample to extract the Schottky barrier, in which no QD (or QR) layer is present; the other way is to fabricate several devices with different geometric lever arms
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