Photoconductive decay in LCVD/PECVD low temperature grown GaN
Photoconductive decay in undoped GaN has been investigated at room temperature using an ArF excimer laser as illuminative source and a boxcar integrator for detection of decay signals. GaN films were grown by combined laser and microwave plasma enhanced chemical vapour deposition at 550°C. The respective room temperature electron concentration and Hall mobility of the films were measured to be in the range 1015–1016 cm−3 and up to 200 cm2/V s. Two time constants, 0.8 and 6 μs, are distinguishable in typical photoconductive decay curves and are associated with a dominant fast recombination and a weaker, slower process via an unidentified defect state respectively. Near-band photoluminescence dominates the emission spectrum with little contribution from the sub-bandgap process often found in the presence of high-density defects.
Using ultrafast optical-pump terahertz-probe spectroscopy, we study the THz dynamics and electronic cooling in few-layer epitaxial and CVD graphene; a microscopic theory of carrier-carrier and carrier-phonon interactions accounts quantitatively for the observed dynamics.