Photocurrent in a hybrid system of 1-thioglycerol and HgTe quantum dots
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Photocurrent in a hybrid system of 1-thioglycerol and HgTe quantum dots Hyunsuk Kim, Kyoungah Cho, Byungdon Min, Jong Soo Lee, Man Young Sung, Sung Hyun Kim1 and Sangsig Kim Department of Electrical Engineering, Korea University, Seoul 136-701, Korea 1 Department of Chemical and Biological Engineering, Korea University, Seoul 136-701, Korea ABSTRACT Photocurrent mechanism in a hybrid system of 1-thioglycerol and HgTe quantum dots(QDs) was studied for the first time in the intra-red (IR) range. 1-thioglycerol-capped HgTe QDs were prepared using colloidal method in aqueous solution; the synthesis and size of the HgTe QDs were examined by x-ray diffraction, Raman scattering, and high-resolution transmission electron microscopy. Absorption and photoluminescence spectra of the capped HgTe QDs revealed the strong excitonic peaks in the range from 900 to 1100nm, because of their widened band gap due to the shrinkage of their sizes to about 3 nm. The wavelength dependence of the photocurrent for the hybred system of the 1-thioglycerol and HgTe QDs was very close to that of the absorption spectrum, indicating that charge carriers photoexcited in the HgTe QDs give direct contribution to the photocurrent in the medium of 1-thioglycerol. In this hybrid system, the photo-excited electrons in the HgTe QDs are strongly confined, but the photo-excited holes act as free carriers. Hence, in the photocurrent mechanism of the this hybrid system, only holes among electron-hole pairs created by incident photons in the HgTe QDs are transferred to 1-thioglycerol surrounding HgTe QDs and contribute photocurrent flowing in the medium of 1-thioglycerol.
INTRODUCTION Semiconductor quantum dots exhibit unique physical properties with respect to bulk regimes. Their advantages include the tunable effective bandgap, the enhanced quantum efficiency due to discrete energy density of states, and the isotropic absorption efficiency independent of polarization of incoming light. Because of these advantages, semiconductor quantum dots (also called nanocrystals or nanoparticles) are very prospective materials for a variety of optoelectronic devices including light-emitting diodes (LEDs)[1-2] and photodetectors [3-8]. For HgTe QDs, the quantum confinement of charge carriers in these QDs due to the shrinkage of their sizes leads to their effective bandgap in the range from ultra-far infrared to near infrared wavelength [9]; note that bulk HgTe has been known as semi-metal material with the bandgap of near zero eV at room temperature. In this study, room-temperature photocurrent of a hybrid system of 1-thioglycerol-capped HgTe QDs in the visible and infrared wavelength
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range is investigated and a simple model is suggested for the description of charge transport mechanism in this hybrid system.
EXPERIMENTS 1-thioglycerol-capped HgTe QDs were synthesized in aqueous solution by the colloidal method [9]. The solution containing the QDs was dropped and dried on silicon substrates, for preparation of films. The synthesized HgTe QDs were char
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