Emnanouil (Manos) Kioupakis
Materials Science & Engineering
University of Michigan
Electronic and Optical Properties of Nitride Semiconductors from First Principles
Location: EB1 Room 3003
Wednesday, March 2nd 2016 - 9:30 am
Group-III-nitrides are important semiconductors for laser and light-emitting diodes (LEDs) in the green to ultraviolet parts of the spectrum. However, the efficiency of current devices is reduced when they operate at high power (efficiency droop), particularly for devices operating at longer wavelengths (green-gap problem). In this talk, I will present results of predictive calculations on how atomic vibrations and alloy disorder enable non-radiative Auger recombination in InGaN alloys, which limits the efficiency of LEDs at high power. I will also discuss how the interplay of Auger recombination with the polarization fields in the quantum wells of polar devices gives rise to the green-gap problem. I will then examine how quantum confinement in atomically thin nitride quantum wells provides additional control over the emission wavelength of optoelectronic devices. Our calculations for the electronic and optical properties of ultrathin (1-4 cation monolayers) GaN and InN quantum wells examine the interplay between quantum confinement, polarization fields, exciton formation, and screening by free carriers on the luminescence properties. The strong quantum confinement in polar ultrathin quantum wells significantly increases the luminescence energy compared to bulk materials, leading to deep-UV emission from monolayer GaN and visible emission from monolayer InN. Excitons are strongly bound and stable at room temperature in these ultrathin layers with binding energies in the 100-200 meV range, which is promising for increasing the LED efficiency. We demonstrate that ultrathin GaN quantum wells are promising for tunable deep-ultraviolet light emission, with applications in sterilization, photolithography, and optical data storage.