Anisotropic morphology of nonpolar a-plane GaN quantum dots and quantum wells

Abstract

The growth of (11–20) or a-plane quantum dots and quantum wells by plasma-assisted molecular-beam epitaxy has been studied. It is shown that Ga-rich conditions lead to the formation of quantum dots, whereas quantum wells are obtained in N-rich conditions. Combining various experimental techniques, it is furthermore demonstrated that quantum dot nucleation along [1–100] and quantum well morphology in the (1–100) plane are influenced by anisotropic growth of AlN buffer layer. Moreover, it is established that peculiar morphological features of quantum dots and quantum wells, in particular the asymmetric shape of quantum dots, are related to the polar character of the [0001] direction in wurtzite nitride material.

Anisotropic strain relaxation and abnormal zigzag shape planar defects in nonpolar a-GaN grown by metalorganic chemical vapor deposition

“…Ga and N atoms in c-GaN are alternatively stacked along the polar [0 0 0 1] crystallographic direction, which leads to spontaneous polarization. In addition, in InGaN/GaN MQWs, stress applied along the same axis contributes to piezoelectric polarization and, thus, total polarization is the sum of spontaneous and piezoelectric polarizations [4]. Total polarization in the c-GaN heterolayers, which can generate internal fields and spatial separation of electron and hole wave functions, leads to a decrease in the efficiency and peak shift [5,6].…”

Nonpolar a-plane GaN films grown on γ-LiAlO2 (302) substrates by low-pressure MOCVD

“…As shown in Fig. 2(b The anisotropic behavior is a specific characteristic of the nonpolar GaN films [13]. Fig.…”

Optical properties of wurtzite GaN/AlN quantum dots grown on non-polar planes: The effect of stacking faults in the reduction of the internal electric field

“…Polar QDs, with the dot axis parallel to the c-axis (c-QDs), are modeled as truncated hexagonal based pyramids [2], as depicted in Fig 2 (a). On the other hand, a-QDs have the truncated trapezoidal based pyramidal shape [9] shown in Fig 2 (b). We shall take the z-axis always parallel to the crystal [0001] direction.…”

“…We show how such stacking faults, acting as zinc-blende (ZB) inclusions, modify the electric polarization inside the QDs and can account for additional electric field reductions. Such reduction, united to the effects of Coulomb correlation [12] or the realistic shape of the dots [9,13], could complete the picture of the QCSE suppression in non-polar QDs.…”

“…In this paper we study the emission of a-plane GaN/AlN QDs and compare it with the predictions of a theoretical model which takes into account the realistic arrow-head shapes of these systems [9]. The absorption spectrum is calculated using a plane-wave expansion method and a 8 × 8 k·p model.…”