Polarization switching phenomena in semipolarInxGa1−xN/GaNquantum well active layers

Abstract

We report the observation of optical polarization switching in In x Ga 1−x N / GaN quantum well active layers, using semipolar ͕1122͖ planes. When the In composition is less than ϳ30%, the emissions related to the top and second valence bands are polarized along the ͓1100͔ and perpendicular ͓1123͔ directions, respectively, similar to earlier studies. On the contrary, as the In composition increases above 30%, the polarizations switch, indicating a crossover between the two valence bands. Because the polarization degree is less sensitive to the well width, the observed polarization switch is ascribed to the InN deformation potentials.

Role of strain in polarization switching in semipolar InGaN/GaN quantum wells

“…Our D 6 value for GaN is smaller in magnitude than that reported by Vurgaftman and Meyer, 22 which was obtained from other deformation potentials by means of the quasi-cubic approximation and not from direct measurements or calculations. For InN, our deformation potential is considerably smaller in magnitude than the value of D 6 = −8.8 eV proposed by Ueda et al, 11 which was deduced indirectly from the dependence of the polarization on indium composition. Before we can investigate the effect of strain on the band structure the strain conditions in the alloy have to be determined.…”

“…This affects the splitting of the uppermost valence bands and hence the polarization of the emitted light. A corresponding optical anisotropy has already been observed for both nonpolar 6-8 and semipolar [9][10][11][12][13][14] devices. This raises the question of how to control the polarization of the emitted light, which is not only of scientific interest but also of technical importance for the performance of light-emitting diodes and laser diodes.…”

“…11,12 The dominant polarization direction of emission was found to switch from [1100] (perpendicular to the c-axis) to [1123] when the In concentration was increased above 30%, but the mechanism responsible for the change in polarization could not be identified. Other experimental studies have found no evidence of polarization switching, however.…”

“…Ueda et al, on the other hand, found no appreciable QW thickness effect. 11 They proposed strain to be the dominant factor, and derived a large shear-strain deformation potential of D 6 =-8.8 eV from their measurements. 11 Strain in (1122) semipolar InGaN grown on GaN substrates is characterized by shear strain and anisotropic strain in the c plane.…”

“…11 They proposed strain to be the dominant factor, and derived a large shear-strain deformation potential of D 6 =-8.8 eV from their measurements. 11 Strain in (1122) semipolar InGaN grown on GaN substrates is characterized by shear strain and anisotropic strain in the c plane. In this work, we calculate the effect of shear strain on the band structure of GaN and InN from first principles.…”