Copper Iron Sulfide Nanocrystal‐Bulk Silicon Heterojunctions for Broadband Photodetection

Abstract

This study describes the optoelectronic characteristics of CuFeS2/Si nanocrystal/bulk heterojunctions. These heterojunctions show a strong photocurrent response under ambient conditions upon excitation from a wide optical spectrum, from 460 to 2200 nm. The devices comprise of a heterojunction formed between heavily doped n‐type silicon (1–100 Ω cm) and copper iron sulfide (CuFeS2) nanocrystal films. Over the spectral range 460–2200 nm the device shows a fast response (20 µs at NIR wavelengths), along with responsivity and detectivity of 4.68 mA W−1 and 5.29 × 109 Jones at 1900 nm wavelength. The photocurrent is further observed to be a nonlinear function of power. These properties of the devices are discussed in terms of a defect filling mechanism. Besides their regular photoresponse described above, the devices also exhibit a slower photothermal response, allowing these to also sense hot objects (450 K; excess 6 mW incident onto the device) within the focal plane, thereby extending the useful sensing range of the devices deeper into the infrared.

Scalable Synthesis of a Sub-10 nm Chalcopyrite (CuFeS2) Nanocrystal by the Microwave-Assisted Synthesis Technique and Its Application in a Heavy-Metal-Free Broad-Band Photodetector

“…The absorption spectrum shown in Figure c indicates that CuFeS 2 nanocrystals have strong absorption in the visible to the near-infrared (NIR) region. Considering the CuFeS 2 nanocrystal as an indirect band gap semiconductor, the optical band gap of the synthesized nanocrystal has been calculated from Tauc’s plot (Figure d), which is ∼1.3 eV. , The widening of the band gap of CuFeS 2 nanocrystals with respect to its bulk structure is due to the strong quantum confinement effect. A Tauc’s plot is also shown in the inset of Figure d by considering the CuFeS 2 nanocrystal as a direct band gap material that shows a band gap of 3.8 eV, can be responsible for the absorption of high energy photons only.…”

“… 31 − 33 Nevertheless, there are very few reports on CuFeS 2 as an active material in the fabrication of a solar cell or photodetector. 34 , 35 This is due to the presence of the 3d orbitals of Fe that create an interband [IB] between the valence band [VB] and the conduction band [CB] of CuFeS 2 . 33 The energy gap between VB and IB is 0.53 eV and indirect in nature, which is not efficient for light absorption.…”

“…Moreover, CuFeS 2 is a direct band gap compound semiconductor with elements belonging to I–III–VI groups . These unique combinations of electrical and optical properties of CuFeS 2 make it a versatile material for applications in different fields including batteries, solar cells, LEDs, and thermoelectric, spintronic, and photoelectrochemical cells. − Nevertheless, there are very few reports on CuFeS 2 as an active material in the fabrication of a solar cell or photodetector. , This is due to the presence of the 3d orbitals of Fe that create an interband [IB] between the valence band [VB] and the conduction band [CB] of CuFeS 2 . The energy gap between VB and IB is 0.53 eV and indirect in nature, which is not efficient for light absorption …”

Toward Green Optoelectronics: Environmental-Friendly Colloidal Quantum Dots Photodetectors

“…Compared to PDs of single-layer CuFeS 2 QDs, the effective separation of electron-hole pairs driven by the electric field at the heterojunction considerably reduced carrier recombination (Figures 6B-E). As a result, the detectivity of the device reached above 10 12 Jones in visible and NIR regions at a bias of 10 V. Similarly, Sugathan et al (2020) fabricated a hybrid PD based on CuFeS 2 QDs and Si with an extended photodetection spectrum from 460 to 2,200 nm. In addition, the device exhibited fall time of 20 μs in the NIR region, which is faster than that of PDs based on bulk Si (typically few milliseconds to seconds).…”

Electronic Structure and Spectroscopy of I–III–VI2 Nanocrystals: A Perspective

“…I–III–VI 2 semiconductor nanocrystals (NCs) drew considerable attention due to their robust synthetic protocols and stability. − Indeed, since their emergence, rapid progress in their synthetic protocols led to I–III–VI 2 /II–VI core/shell architectures that exhibit photoluminescence quantum yields (QYs) in excess of 80%. − It is further noteworthy that these high QYs could be attained in small (∼5 nm diameter) core/shell NCs. , Considerable success in incorporation of I–III–VI 2 NCs into devices also fuelled increased research interest in this class of materials. − This article presents a perspective view of the spectroscopy and electronic structure of these materials. Although our discussion is centered around NCs, we do draw results obtained from both bulk and NCs.…”