Electron Energy Spectra of Single and Multiple AlGaN/GaN Quantum Dots with Spontaneous and Piezoelectric Polarization Ef
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1017-DD08-30
Electron Energy Spectra of Single and Multiple AlGaN/GaN Quantum Dots with Spontaneous and Piezoelectric Polarization Effects Choudhury Jayant Praharaj formerly with Cornell University, Santa Clara, CA, 95051
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 cylindrical quantum dots, which is an approximation to quantum dots with hexagonal-facet shapes recently reported in the literature. 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. 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 states not coincident with continuum energy levels
Introduction Group III nitride semiconductors with wurtzite crystal symmetry have spontaneous polarization in the absence of externally applied electric fields. The spontaneous polarization discontinuities at group III nitride heterojunctions is of the order of 1013 electrons per cm2 [1 ] Further, the nitride semiconductors have large piezoelectric polarizations when they are grown as lattice-matched layers [ 2 ]. Quantum dots built from group III nitride semiconductors are of technological interest as detectors of infrared radiation [ 3 ]. The spontaneous and piezoelectric polarizations in these semiconductors play a crucial role is determining the energy spectra and the transition frequencies in quantum dots. Nitride quantum dots with vertical dimensions along the ( 0001 ) crystallographic axis, or the c-axis, of a few atomic monolayers have been reported based on self-assembly during the Stranski-Krastanow growth mode [ 3,4,5,6 ]. Many of the studies report quantum dot layers stacked vertically above each other. The studies so far have reported vertical
stacking between quantum dot layers of several atomic monolayers. The quantum mechanical coupling between the quantum dot laye
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