Numerical investigation of efficiency loss mechanisms in light emitting diodes and determination of radiative and non-radiative lifetimes for infrared optoelectronics

The year 2015 was defined the international year of light and light-based technologies. This title did not come unexpected, the research activity in solid-state lighting intensified during the last decade striving to improve solid-state light sources in terms of power consumption and fabrication costs. Emerging technologies are going to improve and amplify the scope of applicability of current solid-state lighting technology. This work would like to give a contribution to scientific research in solid-state lighting on two fronts. First, by contributing to the determination of the optical properties of germanium and germanium-tin alloy and second, by searching for remedies to the temperature dependent efficiency loss in GaN/InGaN based blue light emitting diodes. On these premises, this work has been splitted in two parts. In part one, the Auger recombination properties of germanium and radiative and Auger recombination properties for germanium-tin alloy have been calculated. In case of germanium, the application of a minimum biaxial tensile strain turns the material to a direct gap semiconductor, suitable for active and passive optoelectronic applications. On the other hand, the germanium-tin alloy is even more interesting due to its tunable band-gap energy and the capability to turn into a direct gap material above a certain molar fraction. On top of that, both materials may represent cheaper alternatives to materials currently used for the fabrication of high performance photodetectors and active optoelectronic devices. For both materials, the Auger and radiative recombination properties have been determined through a novel numerical approach that applies a Green’s function based model to the full band structure of the material. In part two, the temperature dependent efficiency loss, experimentally detected in a reference GaN/InGaN based single quantum well light emitting diode, has been numerically studied by measn of a commercial simulation software Crosslight APSYS © . The charge transport mechanism in the device has been modeled through an improved drift-diffusion scheme and compared to the real device current-voltage characteristics. Once an agreement between real and simulated current-voltage characteristics was achieved, the impact of Shockley-Read-Hall recombination mechanism on the device internal quantum efficiency function of temperature has been throughfully studied.