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

Abstract

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/MoO x /Ag photodetectors (PDs) have been investigated possibly for the first time. The colloidal CdSe QDs (diameter ∼4.84–5.85 nm) and MoO x 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 × 1012 cm · Hz1/2 · W−1, and 10.88% for 250 °C, 11.2 mA/W, 5.64 × 1011 cm · Hz1/2 · W−1, and 3.62% for 350 °C, and 2.2 mA/W, 4.69 × 109 cm · 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.