In the nitride system, polarization of light is an extraordinary property of quantum wells (QWs) with growth direction inclined to the c-axis. This anisotropy of emission is a direct consequence of strain symmetry in these pseudomorphically grown semipolar and nonpolar oriented layers.

A nonpolar quantum well above a schematic illustration of the wurtzite crystalline structure is drafted in the left part of the image. This property of its emission is expressed by spherical harmonics on top. They reflect the optical polarization of the emitted light in all growth directions. From polar to nonpolar grown QWs, even a switching behavior can be detected, indicated on the surrounding circle.

In their article on pp. 700 L. Schade et al. report on the spectral properties of optically polarized light originating from semipolar and nonpolar InGaN quantum wells at low temperatures. There, only one radiative transition contributes to the emission. All data can be explained by the influence of the varying indium content within the quantum wells of different crystal orientation.

The work of Lewis Z.-Y. Liu et al. (pp. 704) enables high resolution real-time characterisation of LEDs under their working conditions. The figure shows a GaN-based LED chip emitting light on an in-situ biasing TEM holder, on which a TEM lamella has been prepared by FIB. The design ensures that a significant amount of the current goes through the cross-sectional TEM lamella. The paper focuses on using electron holography to determine the electrostatic potential across the LED structure. This experimental platform allows a variety of TEM techniques to be applied to extract a range of information from a working LED at high spatial resolution.