Fig. 1
From: Ultrafast and highly sensitive infrared photodetectors based on two-dimensional oxyselenide crystals
Photodetectors based on 2D Bi2O2Se. a Illustration of photodetector based on 2D Bi2O2Se crystal, with schematic crystal structure of alternatively stacked (Bi2O2)n and Sen layers. The layer thickness is 0.61 nm. b Electronic structure of Bi2O2Se observed by ARPES, which shows an indirect band gap of ~0.8 eV and small effective mass of ~0.14 m0. The spectra under E–EF = −1 eV and around E–EF = 0eV correspond to valence and conduction band, respectively. EF refers to Fermi level, so only tiny conduction band structure under Femi level is observed here. The directions of ARPES mapping are along X–Γ–X directions. The right panel is the corresponding density of states (DOS), which is calculated by integrating signals of the left panel along momentum space. c Optical image of Bi2O2Se device with thickness of ~10 nm and ~16 layers, scale bar 20 μm. d Scanning photovoltage image of the dotted rectangle area of device in c. The 1200 nm laser with power of 150 μW is focused and scanned on the device, while the net photovoltages are recorded as function of laser positions. The photovoltages are measured without external bias. e Line-scanning of photovoltage along dotted line in d. The curve corresponds to the α-plane cut of f. The two peaks correspond with Bi2O2Se-metal junctions. f Spectrogram composed of photovoltage line scans at different incident photon energies (wavelength of incident light). The incident photon numbers are kept still during the measurement, and the incident power is 100 μW at 1200 nm. g Photovoltage and absorbance of Bi2O2Se as function of incident photon energy. Red solid line shows photovoltage trace, which corresponds to β-plane cut of the spectrogram. Black circles show the absorbance of Bi2O2Se film with ~10 nm in thickness
