Study of carrier dynamics in LT GaAs by means of time-resolved emission terahertz spectroscopy

Summary form only given. Biased large aperture semiconductor emitters are widely used to generate ultrashort broadband terahertz (THz) pulses. The temporal shape of such pulses can be determined through a phase sensitive electro-optic or photoconduction sampling technique. The measured profile of the THz pulse then depends on several factors: (i) incoming optical pulse shape, (ii) dynamics of photo-excited carriers in the THz emitter, (iii) far-infrared optics transforming the THz beam, and (iv) receiving antenna or sensor spectral detectivity. We used 80 fs laser pulses at 800 nm generated by a self-mode-locked Ti:sapphire laser to excite biased GaAs samples. They consisted of a 1.3 /spl mu/m layer of MBE-GaAs grown at low temperatures (LT-GaAs) on a semi-insulating GaAs substrate with a 72.5 nm GaAs buffer layer. We studied several samples characterised by different deposition temperatures ranging between 175 and 250/spl deg/C. The irradiated THz waveform was measured using a ZnTe electro-optic sensor (without any focusing optics to avoid the waveform reshaping). The THz signal was studied as a function of several parameters (applied voltage, pump laser intensity, distance between biased electrodes). Lateral scans of the emitter position (with regard to the pump beam) were also performed.