Temperature dependence of the photoelectric conversion quantum efficiency of 4H–SiC Schottky UV photodetectors

Abstract

Ultraviolet Schottky photodetectors based on n-4H-SiC (N d − N a = 4 × 10 15 cm −3 ) epitaxial layers of high purity have been fabricated. Their spectral sensitivity range is 3.2-5.3 eV peaking at 4.9 eV (quantum efficiency is about ∼0.3 electron/photon), which is close to the bactericidal ultraviolet radiation spectrum. The temperature dependence of the quantum efficiency of 4H-SiC Schottky structure has been investigated to determine the temperature stability and the mechanism of the photoelectric conversion process. At low temperatures (78-175 K) the quantum efficiency increases with increasing temperature for all photon energy values and then tends to saturate. We suppose that some imperfections in the space-charge region act as traps that capture both photoelectrons and photoholes. After some time the trapped electron-hole pairs recombine due to the tunnelling effect. At high temperatures (more than 300 K), the second enhancement region of the quantum efficiency is observed in the photon energy range of 3.2-4.5 eV. It is connected with a phonon contribution to indirect optical transitions between the valence band and the M-point of the conduction band. When the photon energy is close to a direct optical transition threshold this enhancement region disappears. This threshold is estimated to be 4.9 eV. At photon energies more than 5 eV a drastic fall of the quantum efficiency has been observed throughout the temperature interval. We propose that in this case the photoelectrons and photoholes are bound to form hot excitons in the space-charge region due to the Brillouin zone singularity, and do not contribute to the following photoelectroconversion process.

High-performance 4H-SiC-based p-i-n ultraviolet photodiode and investigation of its capacitance characteristics

“…At the same time, the surface recombination increase with temperature due to the increase in absorption coefficient, which in turn reduces the responsivity. As a result, this combined effect induces the responsivity to display a relatively temperature-independent behavior [17,18]. Furthermore, the photodiode exhibits a high UV-to-visible rejection ratio (R 266 nm /R 380 nm ), which is higher than 10 3 at 300 K and even above 200 at 450 K. These findings suggest that the fabricated photodiode has "visible blindness" feature and can be used at strong visible and infrared background without any visible/infrared rejection filter.…”

Temperature dependence of current conduction in semi-insulating 4H-SiC epitaxial layer

“…We used $4.0 eV for the electron affinity of 4H-SiC (Ref. 6) and $5.2 eV for the Ni work function. 7 Since the I-V characteristics were measured using dual stair sequence, each I-V characteristic shown in Fig.…”

Fabrication and characterization of n-ZnO on p-SiC heterojunction diodes on 4H-SiC substrates

“…4(b). In this diagram, the electron affinity for ZnO χ ZnO is taken as 4.35 eV [20] and the electron affinity of 4H-SiC is 4.05 eV [21]. The band gap energies of ZnO and 4H-SiC are taken as 3.3 eV, and 3.2 eV, respectively.…”