Heating Effects of Colloidal ZnO Quantum Dots (QDs) on ZnO QD/CdSe QD/MoOx Photodetectors

In this paper, the effects of heat treatment of a colloidal ZnO quantum dot (QD) (diameter ~1.83-2.43 nm) based electron transport layer (ETL) on the performance of ZnO QD/CdSe QD/MoOx/Ag photodetectors (PDs) have been investigated possibly for the first time. The colloidal CdSe QDs (diameter ~4.84-5.85 nm) and MoOx are used as the active layer and the hole transport layer in the PDs, respectively. The photoresponse and response time measured for 250, 350, and 450 °C annealing temperatures of the ETL have been compared. The PDs show the best performance for the annealing temperature of 250 °C. The average response time, dark current, and contrast ratio (i.e., the ratio of photocurrent to dark current) of the PDs are measured as 25.5 ms, -0.02 μA, and 1216 for 250 °C, 31.7 ms, -0.06 μA, and 170.8 for 350 °C, and 56.31 ms, -0.37 μA, and 7 for 450 °C, respectively. The responsivity, detectivity, and external quantum efficiency at a wavelength of 386 nm for an applied bias of -0.1 V are measured as 32.4 mA/W, 1.22 × 1012cm · Hz1/2· W-1, and 10.88% for 250 °C, 11.2 mA/W, 5.64 × 1011cm · Hz1/2· W-1, and 3.62% for 350 °C, and 2.2 mA/W, 4.69 × 109cm · Hz1/2· W-1, and 0.706% for 450 °C, respectively. Thus, the performance of the PDs gets deteriorated at higher annealing temperatures of the ZnO QD-based ETL of the device under consideration.