The high-density effects in the recombination of electron–hole plasma in photoexcited homoepitaxial GaN epilayers were studied by means of transient photoluminescence at room temperature. Owing to the “backward” and “lateral” photoluminescence measurement geometries employed, the influence of stimulated transitions on the decay of degenerate nonthermalized plasma was revealed. The lateral stimulated emission was demonstrated to cause a remarkable increase in the recombination rate on the early stage of the luminescence transient. A delayed enhancement of the stimulated emission due to the cooling of plasma from the initial temperature of 1100 K was observed. After completion of the thermalization process and exhaustion of the stimulated emission, the spontaneous-luminescence decay exhibited an exponential slope that relates to the nonradiative recombination of the carriers. The homoepitaxially grown GaN layer featured a luminescence decay time of 445 ps that implies a room-temperature free-carrier lifetime of 890 ps (considered to be extremely high for undoped hexagonal GaN).

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Optical gain in GaN epilayers, grown by metalorganic chemical-vapor deposition technique on bulk GaN substrates is studied by means of time-resolved luminescence spectroscopy at room temperature. Both stimulated emission and carrier recombination rate are analyzed under high photoexcitation conditions that are close to laser operation regime. Homoepitaxial GaN shows a high value of optical gain coefficient g=7200cm−1 estimated under intense pulsed excitation by a variable stripe method. For comparison, a GaN epilayer grown under identical conditions on sapphire shows a significantly lower value, g=2300cm−1. Larger values of the optical gain coefficient achieved in homoepitaxial GaN are due to the lower density of nonradiative traps. This is proved by the carrier capture time that is estimated right after exhaustion of the inverted population, and has values of τe=970 and 195ps for homo- and heterolayers, respectively.

We report on the development of deep-ultraviolet light-emitting diodes with AlGaN multiple-quantum-well active region for real-time fluorescence lifetime sensing in natural biofluorophores. The peak wavelengths of the devices are 340 and 280 nm, linewidth at half maximum approximately 10 nm, wall-plug efficiency up to 0.9%, output power in the milliwatt range, peak-to-background ratio up to four orders of magnitude, and cutoff frequencies for electrical modulation in the range of 100 MHz. Devices with high-frequency modulated output were demonstrated for frequency domain fluorescence lifetime measurements in basic biological autofluorophores (nicotinamide adenine dinucliotide, riboflavin, tyrosine, and tryptophan) with subnanosecond resolution.

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