Electron cooling behavior in cascading semiconductor double-quantum-well structures

We investigate evaporative electron cooling in cascading semiconductor double-quantum-well (QW) structures. In this cascading double QW structure (QW1 and QW2, where QW2 is on the anode side), one electron absorbs two longitudinal optical (LO) phonons as it travels from the cathode to the anode, for which efficient thermionic cooling is expected. By analyzing the high-energy tail of the photoluminescence spectra, the electron temperature in each QW is determined. When ${\mathrm{Al}}_{0.35}{\mathrm{Ga}}_{0.65}\mathrm{As}$ barriers are used, anomalous electron heating in QW2 due to hot electron distribution above the barrier is observed. By introducing taller barriers (${\mathrm{Al}}_{0.7}{\mathrm{Ga}}_{0.3}\mathrm{As}$) before QW2 to suppress hot electron distribution above the barrier, electron cooling in both QWs by several tens of kelvins is achieved. Furthermore, oscillatory anticorrelated electron temperature change in the two QWs that results from LO-phonon scattering is observed.