Carrier dynamics in GaAs/AlAs ridge quantum wire

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We have investigated the carrier dynamics in the GaAs/AlAs ridge quantum wire by the optical methods. We could solely perform the measurement of the fluorescence spectra and its lifetime.[Experimental]We used the SHG of the femtosecond output pulse from a Ti:Sapphire regenerative Amp. (λ=400nm, 100μJ, 150fs) as the excitation. The samples studied here were the quantum wells, A1458 (AlAs 10nm-GaAs 7nm-AlAs 3nm), A1472 (AlAs 5nm-Al_<0.5>Ga_<0.5>As 170nm-GaAs 6nm-Al_<0.5>Ga_<0.5>As 170nm-AlAs 5nm), A1480 (AlAs 3nm-Al_<0.3>Ga_<0.7>As 283nm-GaAs 6nm-AlAs 3nm) and the ridge quantum wire with the same layer structure. The lifetime measurement of the fluorescence from the sample (10K) was carried out by using a streak camera.[Experimental Results](1) Lifetime measurement in GaAs/AlAs quantum wellsIn the case of strong excitation, we observed the broad fluorescence spectrum. It probably results from that the lowest excited states in quantum well are saturated due to the high density of the excited carriers. In this case, the lifetime was shorter at the shorter wavelength. In the case of weak excitation, we observed the narrow spectrum from the extitons in the quantum well. The measured lifetimes were 1290ps(A1458), 427ps(A1472), 280ps(A1480), respectively. In the sample A1480, the fluorescence at 666 nm of the barrier (Al_<0.3>Ga_<0.7>As) was also observed.(2) Lifetime measurement in GaAs/AlAs ridge quantum wireWe measured the lifetime of fluorescence in A1480 ridge sample. Two peaks were observed at 678 and 725 nm in the fluorescence spectrum. The lifetime of fluorescence was measured to be very short for the wavelength of 660 nm, but to become relatively long at 680 nm. At 700 nm, the fluorescence showed the two-exponential decay and it became the single-exponential deay at 720 nm. At 740 nm, the lifetime was observed to be long again. Based on these measurement, we attribute the fluorescence peaks at 678 nm and 725 nm to side-QW and QWR, respectively.