Coherent Spectroscopy of Semiconductors

Unconventional motional narrowing in the optical spectrum of a semiconductor quantum dot

“…The asymmetry between the power dependences of τ ↓ and τ ↑ stems from the existence of different microscopic processes of various efficiencies in semiconductor physics [12]. The constant value of 10 ps for τ ↓ is consistent with an optical-phonon assisted capture in the traps around the quantum dot [15].…”

“…In fact, in bulk semiconductors or in quantum wells, the standard phenomenology is the exact opposite. An increasing number of photo-created carriers leads to the activation of carrier-carrier Coulomb correlations, and induces the inverse transition from an inhomogeneously broadened Gaussian line to a homogeneous Lorentzian one [12]. In the following, we provide a quantitative analysis of our measurements in the framework of the Kubo theory.…”

“…The saturation value Σ s of the spectral modulation amplitude is thus given by √ N ∆/2. In semiconductor nanostructures, at low temperature carrier escape is known to be much less efficient than the capture process [12]. When τ ↓ /τ ↑ ≪1, the correlation time τ c has approximately a constant value given by τ ↓ whereas Σ scales as 2Σ s τ ↓ /τ ↑ .…”

Dephasing in the quasi-two-dimensional exciton-biexciton system

“…The binding energy of the biexcitons has been investigated in great detail, 1-3 while only little is known about the scattering processes of biexcitons [4][5][6] compared to that of excitons. 7 In four-wave mixing ͑FWM͒ spectroscopy, commonly used to measure scattering processes, the disorder present in nanostructures strongly modifies the FWM response, 8 especially the biexcitonic signal, 9,10 and the analysis of the biexciton scattering is intricate. 11 In a homogeneously broadened system instead, the dephasing rates of exciton and biexciton to ground-state transitions and also of the exciton-biexciton transition can be determined.…”

Dephasing in InAs/GaAs quantum dots

“…The development of four-wave mixing techniques has allowed to measure T 2 in both bulk materials and low-dimensional heterostructures also in the presence of strong inhomogeneous broadening, where a simple linewidth analysis in the spectral domain fails. 2 Recent breakthroughs 3 in the growth of zero-dimensional semiconductor structures strengthen the interest in extracting the homogeneous linewidth of these systems. 4,5 Especially the ''phononbroadening'' is controversial, because the discrete energy level structure is expected to reduce phonon interactions ͑phonon bottleneck͒.…”