Investigations of defects in TiO2/HgTe/MoO3 heterostructures and their influence on transport properties

Abstract

Abstract The need for simple-to-manufacture, solution-processable, tunable infrared active optoelectronic materials led to the development of infrared colloidal quantum dots, whose band gaps may be easily regulated by dimensional constraints resulting from the quantum confinement. Due to electronic deep-level trap states that limit effective mobility and function as effective recombination centers, nanocrystal (NC)-based optoelectronic devices still perform less well than what is predicted theoretically. The performance of NC-based optoelectronic devices can be considerably improved by identifying and passivating these defect levels. In this study, we use low-temperature I–V, C–V, C–F and the microcontroller-based deep level transient spectroscopy (DLTS) system to investigate the defect levels in the FTO/TiO2/HgTe/MoO3/Au device. The I–V measurements at low temperatures demonstrated the existence of exponential trap states, with an activation energy of 0.24 eV and a trap density of 3.18 × 10 17   cm − 3 . Low-temperature C–V and C–F measurements established the existence of deep trap states. With DLTS, we have located two deep trap levels (traps 1 and 2), with energies of 0.25 and 0.46 eV, capture cross-sections 9.7 × 10 − 23 and 4.35 × 10 − 14   cm 2 and a concentration of 2.4 × 10 17   cm − 3 , respectively. The surface states at the HgTe NCs and the oxygen vacancies at the TiO2 are the leading causes of the trap levels, which are primarily present at the interface of the TiO2/HgTe heterojunction. The transport mechanism in these heterojunction devices was happening mainly through these interface trap states. Passivating these defect levels is vital to increase the device effectiveness.