Ultraviolet Photodetectors Based on Nanometer-Thick Films of the Narrow Band Gap Semiconductor PbS

Abstract

Ultraviolet photodetectors (UVPDs) which play important roles in military and civil applications are normally fabricated by using wide band gap semiconductors (WBSs) as building blocks. Unfortunately, the commercialization of UVPDs based on WBSs is often limited by their relatively high fabrication cost owing to the use of very complicated growth instruments. In this work, a sensitive UVPD based on non-WBS lead sulfide (PbS) with a relatively small band gap was proposed. Device analysis revealed that the UVPD made of 48.5 nm PbS nanofilm was highly sensitive to UV illumination at 365 nm. Specifically, the responsivity and specific detectivity under 365 nm illumination were 22.25 A W–1 and 4.97 × 1012 Jones, respectively, which are comparable to or better than most of the conventional WBS-based UVPDs. The PbS nanofilm-based UVPD also exhibits excellent environmental stability. Experimental results and simulations based on technology computer-aided design software confirmed that the abnormal properties of PbS nanofilms are related to the relatively thin thickness and wavelength-dependent absorption coefficients. These results open up an opportunity for narrow band gap semiconductors to realize low-cost-sensitive UVPDs in future optoelectronic devices and systems.

Bias‐Selectable Si Nanowires/PbS Nanocrystalline Film n–n Heterojunction for NIR/SWIR Dual‐Band Photodetection

“…[22,53,54] However, the LDR and fitting value of the device are comparable or even better than those of PbS-based PDs or photoconductive PDs. [22,53] To quantitatively evaluate the device performance, the photoresponse curves of the device with light intensities in Figure 5b,e were analyzed. The noise equivalent power (NEP) and the detectivity (D*) are usually described as follows:…”

“…PbS nanocrystalline film were deposited on the etched SiNWs substrate with the chemical bath deposition method (CBD), avoiding sophisticated epitaxial instruments. [22] Gold electrodes (≈50 nm) vaporized on the insulating layer, and In-Ga alloy was coated on the silicon substrate to form ohmic contacts. [19] A detailed schematic diagram of the preparation process is shown in Figure S1 (Supporting Information).…”

“…As a direct-bandgap semiconductor, the bandgap of PbS is estimated to be 0.6 eV based on the Tauc relation of (𝛼hv) 2 ∝(hv-Eg). [22,37] The tunable bandgap is due to the nanocrystalline nature of the CBD method derived PbS film.…”

“…Materials Synthesis and Device Fabrication: Optimized fabrication of silicon nanowires by Ag-assisted chemical etching procedure has been described in detail elsewhere. [22] In brief, a lightly doped n-type silicon substrate with a 300 nm dioxide insulator layer was cleaned in an ultrasonic bath with acetone, alcohol, and deionized water for 15 min, respectively. Windows with 0.04 (0.2 × 0.2) cm 2 were first defined on the SiO 2 /Si substrate by adhesive tape, followed by dipping into a buffered oxide etch (BOE) solution for 3 min to remove the selected area.…”

“…Lead sulfide (PbS), a typical IR material as a direct narrow bandgap (≈0.41 eV), has demonstrated excellent optical and electrical properties such as high optical absorption, high carrier mobility, and adjustable spectral selectivity. [22][23][24] In contrast to devices made with epitaxial materials, the IRPDs based on PbS nanocrystals were fabricated by simple solution methods with wide tunable bandgap. [25][26][27] Therefore, the combination of Si and PbS can significantly expand the spectral range of Si-based PDs, offering a simplified single junction structure and leveraging the mature fabrication process of Si wafer and PbS nanocrystals.…”