Conditions and possible mechanism of condensation of e–h pairs in bulk GaAs at room temperature

Abstract

A mechanism of the condensation of e-h pairs in bulk GaAs at room temperature, which has been observed earlier, is proposed.The point is that the photon assisted pairing happens in a system of electrons and holes that occupy energy levels at the very bottoms of the bands. Due to a very high e-h density, the destruction of the pairs and loss of coherency does not occur because almost all energy levels inside a 30-60 meV band from the bottom of the conduction band prove to be occupied. As a result, a coherent ensemble of composite bosons (paired electrons and holes) with the minimum possible energy appears. The lifetime of this strongly non-equilibrium coherent e-h BCS-like state is as short as a few hundred of femtoseconds.

Pulse generation with ultra-superluminal pulse propagation in semiconductor heterostructures by superradiant-phase transition enhanced by transient coherent population gratings

“…lasing and SR emission generated from the same 3-section structure at different reverse bias levels and gain currents. SR spectra are always red shifted by 10-20 nm with respect to the peak of lasing as the observed cooperative emission occur at the band gap energy [22][23][24][25]. The peak wavelength of the SR emission is around 890 nm, whereas the centre wavelength of the c.w.…”

“…In general, they have gain and saturable absorber sections of different geometries with different gain/absorber ratios and total cavity lengths. The devices under test are described in detail in our previous publications (see, for instance, [22][23][24][25]). The composition of the GaAs/AlGaAs heterostructures is varied.…”

“…Eqs. (6) and (7) include correlated Gaussian random functions  ± N describing spontaneous noise in a similar manner to that in our previous SR model [25]. The Eqs.…”

“…Indeed, the semiconductor active medium in the GaAs/AlGaAs heterostructures studied does not exhibit any closely spaced gain or absorption lines with a strong anomalous dispersion region, which can be responsible for the fast light effect. However, by contrast to any laser, where the field is coherent while the active medium is incoherent, macroscopically large areas of the coherent macroscopic population exist in the semiconductor during the SR phase transition [22][23][24][25]. It has been previously suggested that the superluminal propagation of light in a coherent amplifier can occur as a results of the pulse reshaping [28][29][30][31][32].…”

“…Various papers have reported SR phenomena in semiconductors at room temperature [22][23][24][25]. Such observations however have led to debate on whether the pulses generated are really akin to those superradiant phenomena observed in low temperature or low density structures [5][6][7], and whether they are different, for example, than those generated by conventional Qswitching [26].…”