Pawel Strak, Pawel Kempisty, Maria Ptasinska, Stanislaw Krukowski
Density functional theory simulations have been used to obtain physical properties of AlN/GaN system. These calculations have shown that chemical band offset of valence bands of AlN and GaN is reverse and equal to -2.43 eV. Combination of these two compounds into multiquantum well (MQW) structure will induce strong electrostatic effect leading to emergence of high magnitude dipole layers at the AlN/GaN interfaces, which were first postulated by {Tersoff Phys. Rev. B 30(8) pp.4874 (1984)} and already identified in these systems by {Romanowski et al. J. Phys. Chem C 114. 14410 (2010)}. Valence band offset becomes small, of order of 0.1 eV, thus almost whole bandgap difference is realized as conduction band offset. Systematic analysis of influence of GaN layers width on the properties of wells have shown that for thickness up to 8 double atomic layers (DALs) i.e. 21 {\AA}, the GaN layers behave as carriers locating potential rather, while for larger thickness it is a standard quantum well. In all cases wells strongly localize quantum states close to valance band maxima (VBM) and conduction band minima (CBM). It was also shown that standard correction screening field gives the same field values in MQWs as the minimal excess electrostatic energy condition. The oscillator strength values were also calculated they rapidly decreases for the well thickness above 8 DALs (\sim21 {\AA}) that is in agreement with experimental observations. Magnitude of Quantum Confined Stark Effect (QCSE) was investigated. Change of transition energy with respect to geometric arrangement which affects electric fields in wells and barriers was also obtained.
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http://arxiv.org/abs/1208.5849
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