Time-resolved reflectivity characterization of polycrystalline low-temperature-grown GaAs

Abstract

Using femtosecond time resolved reflectivity, we have characterized the dynamics of photoinduced generated carriers in a polycrystalline low-temperature-grown GaAs sample. Our measurements are fitted with an analytical expression reliable for low pump power experiments. The sample, which presents no As precipitates, shows an ultrafast subpicosecond response together with a longer picosecond tail that we attribute to the midgap defect states. Moreover, we have observed the influence of surface roughness on the differential reflected signal.

Experimental evaluation of the carrier lifetime in GaAs grown at low temperature

“…Since the change in the optical properties of the material was due to nonequi librium carriers generated by the pump pulse, the thus measured time is equal to the carrier lifetime. The value of τ we obtained is close to the record breaking short carrier lifetimes obtained by various research teams [10][11][12][13][14][15] for LT GaAs epitaxial layers.…”

“…The carrier relaxation dynamics are commonly studied by the pump-probe tech nique [7,[10][11][12][13][14][15]. In this method, an optical pump pulse creates, in the material, a nonequilibrium carrier concentration sufficient for changing the refractive index, whose variation dynamics are recorded with a probe light pulse.…”

Radiative recombination and other processes related to excess charge carriers, decisive for efficient performance of electronic devices

“…Also, LTG GaAs post-growth annealed at temperatures in a range of 600-800°C still showed the subpicosecond photo-excited electron decay (electron trapping time was between 0.2-1 ps) [28,29]. Several experimental techniques consistently proved this fast carrier dynamics in LTG GaAs: photocurrent transients [38], pumpand-probe reflectivity [39], absorption [40], timeresolved luminescence [26], optical pump-THz radiation probe [41], and analysis of THz emission from LTG GaAs photoswitch antennae [42]. Contribution of arsenic precipitates present in annealed LTG GaAs in the excess carrier recombination was strongly debated [18,10].…”

Semiconductors for terahertz photonics applications

“…A part of a pulsed laser beam induces the change in a certain physical characteristic of the sample, and this change is monitored with a second part of the same beam that arrives at the sample at different time delays. Carrier dynamics was documented by pump-probe measurements of several different physical characteristics of LTG GaAs: photocurrent transients [59], dynamic reflectance [60], dynamic transmittance [61], time-resolved photoluminescence [62], and THz conductivity [63]. All these physical characteristics are mainly sensitive to the presence of the non-equilibrium electrons in the sample; therefore, the electron dynamics in LTG GaAs is fairly well understood.…”