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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 32, Number 1
BKCSDE 32(1)
January 20, 2011 

Effects of Curing Temperature on the Optical and Charge Trap Properties of InP Quantum Dot Thin Films
Priyaranjan Mohapatra, Mai Xuan Dung, Jin Kyu Choi, Sohee Jeong, Hyun Dam Jeong*
InP, Quantum dot, Thin films, Charge trap
Highly luminescent and monodisperse InP quantum dots (QDs) were prepared by a non-organometallic approach in a non-coordinating solvent. Fatty acids with well-defined chain lengths as the ligand, a non coordinating solvent, and a thorough degassing process are all important factors for the formation of high quality InP QDs. By varying the molar concentration of indium to ligand, QDs of different size were prepared and their absorption and emission behaviors studied. By spin-coating a colloidal solution of InP QD onto a silicon wafer, InP QD thin films were obtained. The thickness of the thin films cured at 60 and 200 oC were nearly identical (approximately 860 nm), whereas at 300 oC, the thickness of the thin film was found to be 760 nm. Different contrast regions (A, B, C) were observed in the TEM images, which were found to be unreacted precursors, InP QDs, and indium-rich phases, respectively, through EDX analysis. The optical properties of the thin films were measured at three different curing temperatures (60, 200, 300 oC), which showed a blue shift with an increase in temperature. It was proposed that this blue shift may be due to a decrease in the core diameter of the InP QD by oxidation, as confirmed by the XPS studies. Oxidation also passivates the QD surface by reducing the amount of P dangling bonds, thereby increasing luminescence intensity. The dielectric properties of the thin films were also investigated by capacitance-voltage (C-V) measurements in a metal-insulator-semiconductor (MIS) device. At 60 and 300 oC, negative flat band shifts (ΔVfb) were observed, which were explained by the presence of P dangling bonds on the InP QD surface. At 300 oC, clockwise hysteresis was observed due to trapping and detrapping of positive charges on the thin film, which was explained by proposing the existence of deep energy levels due to the indium-rich phases.
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