Effect of occupation of the excited states and phonon broadening on the determination of the hot carrier temperature from continuous wave photoluminescence in InGaAsP quantum well absorbers

An InGaAsP quantum well with a type-II band alignment is studied using continuous wave power and temperature dependent photoluminescence (PL) spectroscopy. The small energy separation between the ground state and first excited state results in significant thermal carrier redistribution and excited state occupation, particularly, with increasing excitation power and temperature. This state filling is evident as a high-energy shoulder in the PL spectra, the same energy region where in the simplest Planck-description the gradient is considered inversely proportional to carrier temperature. The outcome of an excited state occupation in broadening the high-energy PL tail is to perturb the temperature extracted using this analysis; therefore, the true temperature of carriers is not properly evaluated when significant state filling occurs. In addition, broadening of the PL due to phonons at higher temperatures also distorts (or falsely increases) the non-equilibrium “hot” carrier temperature and as such should be considered when using Planck's relation. The role of these two effects is considered and their mutual effect on the analysis of the extracted hot carrier temperature discussed.