The dual role of nitrogen as alloying and confining element in GaAs-based dilute nitride semiconductors.

We examine transport and relaxation dynamics of optically excited electrons in GaAs-based heterostructure layers, involving dilute nitrides in percent-level concentration range. Such heterostructures contain materials with very different mobilities. Drift instead of Hall mobility is determined using a special technique. The value of the mobility of photogenerated electrons in a freestanding, 3% N InGaAsN layer, as part of a two-layer structure of 100 nm GaAs/2 μm nitride, is found to be of the order of 2 cm2/Vs, much lower than other values reported in the literature. The concomitant presence of carriers in the GaAs and nitride layers leads to formation of a barrier at the interface region that hinders electrons to enter in the nitride material. The dwell time of photoexcited electrons in GaAs interfacing the nitride layer is of the order of milliseconds, as seen by photoconductivity transients after pulsed optical excitation, much longer than the resulted time from optical experiments. Comparison of optical with transport properties reveals that the same centers involved in luminescence, that appear to be extended, are responsible also for hopping transport, where they appear as deep states. A theoretical explanation is given. [ABSTRACT FROM AUTHOR]