Enhanced Hot-Carrier Effects in InAlAs/InGaAs Quantum Wells

Abstract

Hot-carrier solar cells require absorber materials with restricted carrier thermalization pathways, in order to slow the rate of heat energy dissipation from the carrier population to the lattice, relative to the rate of carrier extraction. Absorber suitability can be characterized in terms of carrier thermalization coefficient (Q). Materials with lower Q generate steady-state hot-carrier populations at lower levels of incident solar power and, therefore, are better able to perform as hot-carrier absorbers. In this study, we evaluate Q = 2.5±0.2 W · K −1 · cm −2 for a In 0 .52 AlAs/In 0 .53 GaAs single-quantum-well(QW) heterostructure using photoluminescence spectroscopy. This is the lowest experimentally determined Q value for any material system studied to date. Hot-carrier solar cell simulations, using this material as an absorber yield efficiency ∼39% at 2000X, which corresponds to a >5% enhancement over an equivalent single-junction thermal equilibrium device.Index Terms-Hot-carrier solar cell (HCSC), InGaAs, InP, thermalization coefficient, quantum well (QW).

Enhanced hot electron lifetimes in quantum wells with inhibited phonon coupling

“…The PL can be modeled via a generalized Planck radiation law 30,31 :where, is the emitted photon energy, A is the absorptivity, Δ μ is the chemical potential or quasi-Fermi-level separation under laser excitation, and T C represents the non-equilibrium hot carrier temperature. 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 .…”

Photoluminescence Study of the Interface Fluctuation Effect for InGaAs/InAlAs/InP Single Quantum Well with Different Thickness

“…Second, the wavelength of InGaAs/InAlAs QW inter-band transitions can cover the standard 1.31- and 1.55-μm optical communication wavelengths [13]. Third, the large conduction-band offset of the InGaAs/InAlAs system enables a strong electron confinement and subsequently a high-temperature stability and a high-speed modulation capability for InGaAs/InAlAs devices [14, 15]. This makes these structures very attractive and suitable for quantum cascade lasers, inter-subband detectors, and devices based on nonlinear optical properties [16–18].…”

Experimental evidence of hot carriers solar cell operation in multi-quantum wells heterostructures

“…(1), U is the luminescence emission, hx is the photon energy, A is the absorption, X is the solid angle of emission, h is the reduced Planck's constant, and c is the speed of light. Essentially, one may extract (i) the carrier temperature T when measuring the slope of the PL signal at high energy and (ii) the QFLs Dl from the absolute intensity of the PL signal and using the previously determined value of T. 17,18,[24][25][26] Interestingly, it is possible to extract T and Dl from Eq. (1) from different spectral ranges, i.e., corresponding to different transitions, therefore to either different electron populations or different materials or device regions.…”

“…18,25 Such high values had already been anticipated, based solely on carrier temperatures. 17,18,28 To go beyond, it is necessary to evidence that the existence of high carrier temperatures can indeed be correlated into additional electrical work. Our approach was to measure the QFLs in this system as it represents the work generated per electron-hole pair (free energy).…”