Jilin University: Realization of Si detectors with ultraviolet band external quantum efficiency exceeding 70%

Si photodetectors (PDs), as the most commonly used fundamental component of the devices, are widely used in optoelectronic devices for their broadband spectral response, ultra-high responsivity, and low-cost fabrication process. However, limited by the high reflection coefficient and the shallow penetration depth of UV radiation, Si PDs have a low response to ultraviolet (UV) light (ex-quantum efficiency close to 0% in the 200?300 nm range). While a wide range of researchers have explored various improvement strategies, obtaining high performance comparable to the response in the visible to near-infrared band remains challenging.

Recently, the group of Prof. Hongwei Song (corresponding author) at the State Key Laboratory of Integrated Optoelectronics, School of Electronic Science and Engineering, Jilin University, reported a three-element (Cr3+, Yb3+, and Ce3+)****-doped CsPbCl3 chalcogenide quantum dots (PeQDs) synthesized by using a high-temperature thermal injection method, and The high performance in the ultraviolet (UV) and near-infrared (NIR) wavelengths was achieved by coating the Si surface with PeQDs. The paper is entitled "Extremely efficient quantum-cutting Cr3+, Ce3+, Yb3+ tridoped perovskite quantum dots for highly enhancing the ultraviolet response of Silicon photodetectors". response of Silicon photodetectors with external quantum efficiency exceeding 70%" was published in Nano Energy.

Link to the paper:

/science/article/pii/S2211285520308557

The results of the study show that the quantum yield of CsPbCl3 increases from 8% to 82% when doped with Cr3+ ions at a doping concentration of 8.2%. to 82%, while exhibiting excellent stability. After 250 days of placement, the doped PL intensity remained essentially unchanged; whereas the undoped PeQDs decayed the PL intensity by 52% after five days of placement. This property mainly comes from (1) the substantial reduction of the defect state density after doping, and (2) the disappearance of the major defective Cl vacancies before doping after doping by DFT calculations.

Figure 1. (a) Crystal structure; (b) TEM images before and after doping; change of (c) crystal plane spacing with (d) XRD diffraction peaks before and after doping; (e) XPS image after doping.

Figure 2. (a) Absorption images, (b) PL images and (c) quantum yield changes for different Cr3+ doping levels; (d) comparison of the long time PL intensity between undoped and Cr3+-8.2% doping; (e) comparison of defect density and fluorescence lifetime with different Cr3+ doping levels; (f) calculation of defect levels before and after doping.

Figure 3(a) absorption spectra show that the absorption in the UV band, especially in the deep UV band, is substantially enhanced after the addition of rare earth ion Ce3+. This is mainly due to the 5d high energy state of Ce3+ ion. And the enhanced quantum yield is due to the fact that the emission energy level of Ce3+ provides a channel for bandgap matching between PeQDs and Yb3+ ions, which greatly increases the quantum yield of quantum clipping of Yb3+ ions to 175%. The tri-ion doped CsPbCl3: Cr3+, Yb3+, Ce3+ PeQDs coated on the Si surface achieved an external quantum efficiency of more than 70% in the 200?400 nm range, which is comparable to that in the visible and near-infrared bands. (Quantum clipping refers to the physical phenomenon that fluorescent materials emit two small-energy photons for every large-energy photon absorbed, with a theoretical quantum yield of 200%.)

Figure 3. Optical characterization of single-element, two-element, and three-element doping and energy band interpretation.

Figure 4. (a) Schematic diagram of SiPDs integrated with quantum clipped PeQDs under full spectrum illumination. (b) Photocurrents of Si PDs, CsPbCl3: Cr3+, Yb3+ PeQDs-coated Si PDs, and CsPbCl3: Cr3+, Yb3+, Ce3+ PeQDs-coated Si PDs under 240 nm, 360 nm, and 980 nm illumination. (c, d) Responsivity and external quantum efficiency of the three devices. (e) Time-resolved photocurrents of PDs under 360 nm illumination. (f) Photocurrent of CsPbCl3:Cr3+, Yb3+, Ce3+ PeQDs coated Si PDs over time.

Overall, this study presents a new strategy to increase the quantum yield of PeQDs and improve the poor response of Si PDs in the UV band. It provides ideas for synthesizing other quantum dots or nanocrystalline materials with high quantum yields; it also promises to enhance the performance of other UV photodetectors by utilizing the absorption enhancement strategy of rare-earth ion Ce3+ doping in the UV band. (Text: Uncalculated)