Defect studies on short-wave infrared photovoltaic devices based on HgTe nanocrystals/TiO₂ heterojunction

Abstract

Narrow bandgap (<0.5 eV) colloidal semiconductor nanocrystals (e.g. mercury chalcogenides) provide practical platforms for next generation short wave infrared, mid wave infrared and long wave infrared optoelectronic devices. Until now, most of the efforts in the field of infrared active nanocrystals have been taken on synthesizing nanocrystals, determining quantum states and building different geometries for optoelectronic devices. However, studies on interface trap states in the devices made from these narrow band gap nanocrystals are mostly unexplored. Herein, we investigate the defects or traps in these nanocrystals-embedded devices, which will be critical for improving their optoelectronic performance. In this article, we fabricate HgTe nanocrystals/TiO 2 based photovoltaic devices and used capacitance-voltage (C-V) and deep level transient spectroscopy (DLTS) to investigate and obtain quantitative information on deep level trap states. Interestingly, frequency dependent C-V measurements show two peaks in the capacitance at lower frequency (<40 kHz), which is attributed to the presence of trap states. However, at high frequency the presence of a weak hump-like structure almost at the center of above two peaks validate the role of interface traps. DLTS studies show that traps at the interface of HgTe nanocrystals/TiO 2 acts as recombination centers having activation energies of 0.27, 0.4 and 0.45 eV with corresponding trap densities of 1.4 × 10 10 , 1.9 × 10 11 and 1.5 × 10 11 cm −3 and estimated capture cross-sections of 6.3 × 10 −14 , 7.5 × 10 −17 and 3.7 × 10 −14 cm 2 , respectively. In this work, DLTS has revealed the existence of interface trap states and the frequency dependent capacitance measurements corroborate the effect of charge storage on the heterostructures built from these nanocrystals that helps in the development of futuristic devices.

Enhanced Response Speed in 2D Perovskite Oxides-Based Photodetectors for UV Imaging through Surface/Interface Carrier-Transport Modulation

“…Various 0D materials, such as CsPbBr 3 quantum dots, HgTe nanocrystals, and PbS quantum dots, were hybridized with low-dimensional metal oxides to modulate the surface/interface charge behavior and optimize the photodetector performance. Due to the intriguing interfacial charge transfer behavior, the mixed dimensional heterojunction has shown fascinating properties beyond the individual metal oxides. − The decoration of 0D materials also changes the condition of the exposed material surface, thereby influencing the interaction of the photocarriers with chemisorbed foreign atoms or molecules. , Nitrogen-doped graphene quantum dots (NGQDs), an attractive carbon material, have extraordinary optical and electrical characteristics due to their pronounced quantum confinement and edge effects. The electron-rich nitrogen atoms endow NQGDs with extensive delocalized electrons and high charge carrier density, making them more favorable for potential optoelectronic devices. − NGQDs have been reported to exhibit superior electron transfer/reservoir properties when incorporated into metal oxides, resulting in the high sensing performance of the hybrid structure. − Moreover, compared with 0D materials mentioned above, NGQDs have the advantages of low toxicity, high chemical stability, and low cost .…”

Mercury chalcogenide colloidal quantum dots for infrared photodetection: from synthesis to device applications

“…This process could be repeated over multiple cycles to reach a thick enough and contiguous conductive QD film. 1,2-Ethanedithiol (EDT) is a firm favourite choice as a short bifunctional ligand to be adopted for the ligand substitution of a series of spin/cast deposited films of Hg chalcogenide QDs, 10,68,75,79,[87][88][89][90][91] and for the HgTe/CdSe core-shell nanoplatelet (NPL) thin films. 92 The process should be done in a dry N 2 gas environment in a glove-box as the dithiol crosslinked film is sensitive to air and moisture exposure.…”

Current–voltage characteristics and deep-level study of GaN nanorod Schottky-diode-based photodetector

“…Kolkovsky et al also demonstrated deep-level defects in a GaN NR ensemble using the DLTS technique [7]. Recently, the DLTS technique has been used to identify the deep traps in photodetector (PD) devices [8]. The trap states in the semiconductor mid-gap region restrict the photogenerated electrons from reaching the conduction band, so the photocurrent generation is inhibited in the device.…”