Dynamics of thermalization in GaInN/GaN quantum wells grown on ammonothermal GaN

In this work, we present measurements of the dynamics of photoexcited carriers in GaInN/GaN quantum wells (QWs) grown on ammonothermal GaN, especially thermalization and recombination rates. Emission properties were measured by time-resolved photoluminescence (PL) and electroluminescence spectroscopy. Due to the use of high quality homoepitaxial material, we were able to obtain very valuable data on carrier thermalization. The temperature dependence of the QW energy observed in PL shows characteristic S-shape with a step of about 10meV. Such a behavior (related to thermalization and localization at potential fluctuations) is often reported for QWs; but in our samples, the effect is smaller than in heteroepitaxial InGaN/GaN QWs due to lower potential fluctuation in our material. Absorption properties were studied by photocurrent spectroscopy measurements. A comparison of emission and absorption spectra revealed a shift in energy of about 60meV. Contrary to PL, the QW energy observed in absorption decreases monotonically with temperature, which can be described by a Bose-like dependence E(T) = E(0) - lambda/(exp(theta/T) - 1), with parameters lambda = (0.11 +/- 0.01) eV, theta = (355 +/- 20) K, or by a Varshni dependence with coefficients alpha = (10 +/- 3) x 10(-4) eV/K and beta = (1500 +/- 500) K. Taking into account absorption and emission, the fluctuation amplitude (according to Eliseev theory) was sigma = 14 meV. The time resolved PL revealed that in a short period (<1 ns) after excitation, the PL peaks were broadened because of the thermal distribution of carriers. We interpreted this distribution in terms of quasi-temperature (T-q) of the carriers. The initial T-q was of the order of 500K. The thermalization led to a fast decrease of T-q. The obtained cooling time in the QW was tau(C) = 0.3 ns, which was faster than the observed recombination time tau(R) = 2.2ns (at 4K). (C) 2013 AIP Publishing LLC.