Energy harvesting from waste heat by using InAs quantum dots

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The research of FY28 has been focused on characterizing the electronic structure of InAs quantum dots (QDs) by terahertz(THz) spectroscopy and investigating THz photovoltaic effect in various types of nanomaterials, such as single molecules and nanowires.(1) Fabricating QD single electron transistors (SETs) and performing THz spectroscopy measurements.We have grown InAs self-assembled QDs by MBE, and fabricated nanogap electrodes to contact single QDs for THz measurements. Previously, the fabrication yield was very low due to the random distribution of QDs. We have used "QD mapping" technique to improve the fabrication yield of QD-SETs by ~10 times (from ~1% to ~10%). Furthermore, the mapping technique allows us to choose a particularly target dot other than randomly chosen dot. We performed THz spectroscopy for the fabricated QD-SETs. The photocurrent is increased from ~1 pA to currently ~10 pA, probably due to the improved conductance between QDs and well aligned electrodes.(2) Investigating THz photovoltaic effect in other nanomaterials.We tried to find THz photovoltaic effect in other interesting nanomaterials, such as single molecules and nanowires. We have measured the photocurrent through a single molecular transistor, which is induced by the THz excited resonance of the molecular. The result is now in review in the famous journal of Nature photonics. Besides this, by the international collaboration with Peking Unviersity, we have fabricated InAs nanowire SETs for THz measurements.