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Title: Ultrafast carrier dynamics in P doped InGaAs GaAs quantum dots
Author: Cesari, Valentina
ISNI:       0000 0004 2748 0665
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2009
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In this PhD project the effect of p doping on the carrier dynamics in InGaAs quantum dot amplifiers emitting near 1.3/mi at room temperature has been investigated by transient differential transmission spectroscopy (DTS) and four-wave mixing (FWM) experiments in a heterodyne detection scheme. From DTS experiments, an absorption bleaching on the order of few hundreds of ps and an ultrafast gain recovery were measured at operating condition, i.e. room temperature and with current injection. The faster absorption bleaching recovery observed in p doped amplifiers has been attributed to the carrier-carrier scattering due to built-in holes. Conversely, the gain compression recovery is limited by the lack of an electron reservoir in the dots which has been demonstrated in doped amplifiers. These findings should help in elucidating the role of p doping in the design of QD-based devices with high-speed performances. Temperature dependent DTS measurements have confirmed this interpretation and lead to a microstate model developed at 20 K to represent the gain dynamics. At room temperature the combined study of the gain and refractive index dynamics allows us to measure the line width enhancement factor. We observed that p doping is effective in reducing this parameter. By FWM experiments, the polarization decay of ground state excitonic transitions in the temperature range from 5K to 210 K has been measured to obtain the zero-phonon line (ZPL) width and its contribution to the homogeneous line shape. The temperature-dependent ZPL width is reproduced by a thermally-activated behaviour. This finding has been discussed in the framework of exciton-phonon interactions. Coulomb interaction is investigated by measuring the dephasing time versus injected current at 20 K. From measurements of the homogeneous broadenings of exciton and biexciton transitions we demonstrated that the carrier capture dominates on pure dephasing in these strongly confined dots. Moreover, a much faster dephasing is observed in p doped devices due to Coulomb interaction between built-in holes.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available