A Mystery Wrapped in an Enigma: Optical Properties of InGaN Alloys

Abstract

The high efficiency of luminescence from InGaN has underpinned widespread recent developments in blue-green optoelectronics. A loose consensus on the nature of the luminescence has emerged in the last three years. Localisation of excitation, whether by composition fluctuations or self-formed quantum dots, appears to tilt the balance in favour of radiative recombination, despite the presence of huge densities of extended defects found in device-grade' material by electron microscopy. The luminescence is lowered in energy with respect to the excitation by internal electric fields. What is not clear at present is the relationship between the composition and the structure: what exactly is responsible for optical effects in this material We have argued previously that, contrary to accepted wisdom, current theoretical treatments fail to give a satisfactory account of the dependence of the optical energies on the composition of InGaN. We now advance a strong form of this argument: present theoretical treatments of light-matter coupling may be inadequate to take account of the complexities of structure inherent in this, or any other, luminescent material.