Channels of radiative recombination and phase transitions in a system of nonequilibrium carriers in a Si0.93Ge0.07/Si thin quantum well

The “exciton gas-plasma” transition (the Mott transition) in a Si_0.93Ge_0.07/Si thin quantum well is investigated using low-temperature photoluminescence. It is demonstrated that this transition is smooth and occurs in the concentration range from approximately 6 × 10¹⁰ to 1.2 × 10¹² cm^?2. At a temperature of 23 K and excitation densities of higher than 10 W/cm², the shape and location of the luminescence line associated with the electron-hole plasma remain unchanged with an increase in the pump density. This can indicate the occurrence of an “electron-hole gas-liquid” transition. It is shown that, in the spectrum of the quantum well, the luminescence of boron-bound excitons dominates at liquid-helium temperatures and low excitation densities, whereas the free-exciton luminescence dominates at temperatures above 10 K. The influence of the homogeneous and inhomogeneous broadening on the electron-hole plasma and exciton luminescence is discussed.