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Electron Energy Spectra of Single and Multiple AlGaN/GaN Quantum Dots with Spontaneous and Piezoelectric Polarization Effects

Published online by Cambridge University Press:  01 February 2011

Choudhury Jayant Praharaj
Choudhury Jayant Praharaj*
Affiliation:
cjp1414@yahoo.com, Unaffiliated, Unaffiliated, 1901 Halford Avenue, Apt 74, Santa Clara, CA, 95051, United States
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Abstract

We present numerical calculations of electron spectra of single and multiple coupled quantum dots based on Aluminium Gallium Nitride / Gallium Nitride heterostructures. The effect of spontaneous and piezoelectric polarization on the confinement potential seen by the electrons is taken into account through bound interface sheet charges. We also calculated the spectra without polarization effects for reference. For some quantum dot dimensions, the energy eigenvalues shift by several hundred meVs due to the polarization charges. We calculate the spectra for the two cases of box-shaped and cylindrical quantum dots. The latter case is an approximation to quantum dots with hexagonal-facet shapes recently reported in the literature. The quantum dots in our calculations are surrounded by vacuum in the lateral direction, but the same qualitative conclusions will hold if the dots are embedded in some material, as long as the barrier heights are large. For GaN vertical confinement of less than 30 angstroms, most of the bound states are associated with the lowest eigenvalue of the vertical confinement potential. This is also true for higher vertical confinement dimensions because the triangular potential seen by the electrons is the same for the lowest energy eigenstates. The electric field in the vertical direction is a strong function of the aluminium concentration in the AlGaN layer. As the AlGaN layer composition is varied from very high Al concentration to medium Al concentration, the spectra shift by several hundred meVs, referred to the onset of the continuous spectra. The transition frequencies between bound states and between bound and the lowest continuum states lie in the low to the high infra-red range, and can be varied over a wide range by both the dimensions and the barrier aluminium concentration. For the case of 4 coupled quantum dots formed by repeated AlGaN/GaN heterojunctions, we find that the polarization-induced electric fields lead to excessive band-bending and as a consequence there are fewer bound states compared to the spectrum calculated without polarization effects.

Keywords

III-Vnanoscalepiezoelectric
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1017 , 2007 , 1017-DD08-30
Copyright
Copyright © Materials Research Society 2007

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