Thermal-equilibrium relation between the optical emission and absorption spectra of a doped semiconductor quantum well

We report experimental demonstration of the Kennard-Stepanov (KS) relation, a fundamental equilibrium relation determined by absolute temperature, between photoluminescence (PL) and PL-excitation spectra of a doped quantum well. With the resonant excitation PL measurement technique, the KS relation has been fulfilled at 5-220 K, thanks to the thermal bath provided by the resident carriers introduced with the doping. Crossover to quasi thermal or nonthermal carrier distributions has also been characterized quantitatively via systematic off-resonant excitations.