14:30 〜 14:45
▲ [15p-D411-5] Electron cooling/heating behavior in quantum cascade cooling structures
キーワード：semiconductor, heterostructure, thermionic cooling
Managing rapid increase in thermal power densities associated with device miniaturization is a major technological challenge. Development of new efficient cooling technologies is therefore urgently required for future progress in electronics. Solid-state cooling devices can be one answer, owing to their high efficiency and compatibility for integration. To achieve efficient cooling, we have been working on semiconductor double barrier heterostructures to utilize the thermionic cooling effect.
In this work, we have studied a multiple quantum well (QW) structure, the quantum cascade cooling (QCC) structure. The structure consists of two 5 nm-thick AlGaAs QWs with different Al compositions (x = 0.1 for QW1 and 0.2 for QW2) sandwiched by AlGaAs barriers. In this structure, one electron can absorb a couple of phonons as it cascades through the multiple QW structure, which may achieve better cooling than the single QW structure.
To clarify the electron cooling behavior, we measured voltage-dependent photoluminescence (PL) spectra of the sample. Figure 1(b) shows the PL intensities from the 2 QWs. When V = ~0.4 V, PL intensity of QW2 is almost quenched, which is most likely due to resonant depopulation of QW2 by LO phonon emission. Another interesting feature in Fig. 1(b) is that the PL intensities of QW1 and QW2 gradually approach each other, which is due to resonant tunneling between QW1 and QW2.
Next, PL spectra from bulk n-GaAs, QW1, and QW2 were analyzed and electron temperatures in the respective layers were determined as a function of V (see Fig. 1(c)). Remarkably, electrons in QW1 is cooled, while electrons in QW2 are significantly heated at around V=0.4V, where the quenching in PL from QW2 is observed. Furthermore, we note that the electron temperatures in QW1 and QW2 become almost equal at the voltage where we expect resonant tunneling. More details will be discussed at the presentation.
In this work, we have studied a multiple quantum well (QW) structure, the quantum cascade cooling (QCC) structure. The structure consists of two 5 nm-thick AlGaAs QWs with different Al compositions (x = 0.1 for QW1 and 0.2 for QW2) sandwiched by AlGaAs barriers. In this structure, one electron can absorb a couple of phonons as it cascades through the multiple QW structure, which may achieve better cooling than the single QW structure.
To clarify the electron cooling behavior, we measured voltage-dependent photoluminescence (PL) spectra of the sample. Figure 1(b) shows the PL intensities from the 2 QWs. When V = ~0.4 V, PL intensity of QW2 is almost quenched, which is most likely due to resonant depopulation of QW2 by LO phonon emission. Another interesting feature in Fig. 1(b) is that the PL intensities of QW1 and QW2 gradually approach each other, which is due to resonant tunneling between QW1 and QW2.
Next, PL spectra from bulk n-GaAs, QW1, and QW2 were analyzed and electron temperatures in the respective layers were determined as a function of V (see Fig. 1(c)). Remarkably, electrons in QW1 is cooled, while electrons in QW2 are significantly heated at around V=0.4V, where the quenching in PL from QW2 is observed. Furthermore, we note that the electron temperatures in QW1 and QW2 become almost equal at the voltage where we expect resonant tunneling. More details will be discussed at the presentation.