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

Abstract

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. Copyright © 2017 John Wiley & Sons, Ltd.

Quantitative experimental assessment of hot carrier-enhanced solar cells at room temperature

“…Figure 4c shows the carrier temperature as a function of the excitation power. We observe a temperature increase of more than 1300 K above the room temperature for carrier in the QW (i.e 1300 K above the carrier temperature in the barrier) -a range of temperature already reported in the litterature [23,25]. We have previously demonstrated that this surplus amount of heat can be converted into a gain in voltage via a Richardson emission of hot carriers (also seen as a pseudo-Seebeck effect) [20].…”

“…Today we find a plethora of promising research on the development and characterisation of hot carrier absorber [15][16][17][18][19][20][21][22]. However, the optical methods used to obtain carrier temperature can be inaccurate when dealing with nanostructures and high excitation fluxes [23][24][25]. Meanwhile, several studies have been performed towards completed devices; especially electrical investigation to validate energy selective contacts [26][27][28]38].…”

Enhanced hot electron lifetimes in quantum wells with inhibited phonon coupling

“…In the simplest case, taking a linear fit to the high-energy tail of the natural logarithm of a PL spectrum determines the carrier temperature 14,15,24,25,32 . However, such an analysis can be problematic in the case of QWs, where higher carrier excitation (increased laser excitation) and/or increased temperature results in the redistribution and thermal occupation of carriers in the higher energy subbands of the QW 31,33 . These effects serve to broaden the PL in low-dimensional systems at high energy, independent of the carrier temperature.…”

Hot carrier solar cells and the potential of perovskites for breaking the Shockley–Queisser limit

“…Additionally, we would like to note, that care has to be taken when carrier temperatures for nanostructures are solely based on PL studies, as the contribution of higher electronic states in the wells can have non-trivial effects on emission spectra. 67 Early on, a slower carrier cooling in GaAs/AlGaAs QWs compared to bulk GaAs was observed and sparked great interest into these structures (consider Fig. 5(b) for a comparison of transient PL spectra).…”