Structural and electronic properties of elastically strained InN/GaN quantum well multilayer heterostructures: Structural and electronic properties of elastically strained InN/GaN quantum well multilayer heterostructures

An important step towards optimization of InN/GaN based devices is identification of the structural characteristics of the corresponding interfaces since the favourable bonding configurations determine materials polarity and consequently the direction of spontaneous polarization. We have addressed this issue through calculations on InN/GaN interfaces comprising misfit dislocations (Kioseoglou et al., J. Mater. Sci. 43, 3982 (2008) [5]). In our present study, additional calculations are performed on subcritical thickness InN/GaN QWs, which exhibit lower dislocation densities as well as reduced InN decomposition and are currently implemented in the fabrication of near-UV light emitting diodes. Ab initio calculations are performed under modified pseudopotentials, accurately reproducing the InN and GaN band gap values, on supercells comprising multilayers of one monolayer (ML) thick InN elastically strained in 5 nm thick GaN barriers having a wurtzite or zinc blende stacking at the interface. The former is found to be energetically favorable. Subsequent calculations on supercells comprising 1 ML thick InN in 8 and 11 nm thick GaN barriers as well as 3 ML InN in 11 nm thick GaN, depict a variation in III-N bond lengths. This variation becomes more significant as the barrier thickness decreases or the QW thickness increases. Hence the strain and consequently piezoelectric polarization are modified. Our results scrutinize recent experimental observations and could prove beneficial for tailoring the optoelectronic properties of InN/GaN QWs. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim