A comprehensive review of semiconductor ultraviolet photodetectors: from thin film to one-dimensional nanostructures

Abstract

Ultraviolet (UV) photodetectors have drawn extensive attention owing to their applications in industrial, environmental and even biological fields. Compared to UV-enhanced Si photodetectors, a new generation of wide bandgap semiconductors, such as (Al, In) GaN, diamond, and SiC, have the advantages of high responsivity, high thermal stability, robust radiation hardness and high response speed. On the other hand, one-dimensional (1D) nanostructure semiconductors with a wide bandgap, such as β-Ga2O3, GaN, ZnO, or other metal-oxide nanostructures, also show their potential for high-efficiency UV photodetection. In some cases such as flame detection, high-temperature thermally stable detectors with high performance are required. This article provides a comprehensive review on the state-of-the-art research activities in the UV photodetection field, including not only semiconductor thin films, but also 1D nanostructured materials, which are attracting more and more attention in the detection field. A special focus is given on the thermal stability of the developed devices, which is one of the key characteristics for the real applications.

Figure 1.

Bandgap and cutoff wavelength of AlGaN dependent on the Al mole fraction.

Figure 2.

Schematic photodetector structures based on III-Nitride semiconductors. (Reprinted from Reference [27]).

Figure 3.

Spectral response of AlGaN-based Schottky barrier photodiodes for different Al mole fraction. (Reprinted from Reference [7]).

Figure 4.

(a) Structure of Schottky-type back-illuminated photodetectors; (b) plan view of the contacts. (Reprinted from Reference [47]).

Figure 5.

(a) The typical dark I-V characteristics for MSM photodetector without and with CaF₂ insulator; (b) Photocurrent spectra measured under the illumination of xenon lamp at the applied voltage of 1 V. (Reprinted from Reference [64]).

Figure 6.

(a) I-V characteristics and responsivity in the dark and upon 338 nm light illumination. The inset shows the responsivity dependence on the applied voltage; (b) Time response upon 350 nm light illumination measured by a mechanical chopping method. (Reprinted from Reference [64]).

Figure 7.

(a) Schematic illustration of band diagram to explain reflection and transparent type photocathode device in case of III-V nitride semiconductor. (b) Band diagram of p-AlGaNfrom the band-bending value and position of VBM evaluated by hard X-ray photoemission spectroscopy at Spring-8.

Figure 8.

Wavelength dependence of quantum efficiency for photocathodes of Mg-doped Al_xGa_1-xN films on Si (111) substrates (reprinted from Reference [67]).

Figure 9.

Fabrication process of transparent photocathode based on GaN film grown on Si substrate.

Figure 10.

Dark I-V characteristics of the MSM diamond photoconductor (reprinted from Reference [91]).

Figure 11.

I-V characteristics of the photoconductor in comparison with a typical MSM photodetector during 220 nm light illumination (reprinted from Reference [91]).

Figure 12.

(a) Time response of the photoconductor upon 220 nm light illumination measured by a mechanical chopping method and (b) time-resolved photoresponse upon a 193 nm excimer laser recorded by an oscilloscope with a 50 Ω impedance (reprinted from Reference [91]).

Figure 13.

Dependence of the responsivity at 220 nm light on the electrode spacing (a) at a fixed voltage of 1 V and (b) at an electric field of 2 × 10⁴ V/cm (reprinted from Reference [93]).

Figure 14.

Spectral response of a Schottky detector with a semitransparent dotted Schottky contact at various biases (reprinted from Reference [97]).

Figure 15.

Photocurrent transport mechanism in a nanowire (reprinted from Reference [105]).

Figure 16.

(a) Cross-sectional SEM image of as-grown nanowires; (b) 45°-tilted SEM image of a mesa photodetector; (c) Schematic representation of a mesa photodetector (reprinted from Reference [113]).

Figure 17.

Photoresponse properties of the bridged β-Ga₂O₃ nanowires. (a) Time-dependent photoresponse measured in the air under 254 nm illumination; (b) Photocurrent decay process of the device; (c) I-V characteristics of the device in the dark, under 365 nm and 254 nm light illumination; (d) Spectral response of the bridged β-Ga₂O₃ nanowires revealing that the device is blind to solar light (reprinted from Reference [117]).

Figure 18.

Typical photoresponse spectrum of SnO₂ nanowire.

Figure 19.

Dependence of the saturated dark current and photocurrent of the diamond photodiode under 220 nm light illumination with an intensity of 26 μW/cm² at a reverse bias of 20 V on the annealing temperatures and times. (Reprinted from Reference [6]).

Figure 20.

(a) Dark I-V characteristics of the MIS photodetector as the temperature was elevated from RT to 523 K; (b) The PDCR variation as the measurement temperature at −1 and −3 V. (Reprinted from Reference [8]).

Figure 21.

Photoresponse properties of the β-Ga2O3 nanowire based photodetectors at various elevated temperatures. (a) Dark current-voltage characteristics at various temperatures. (b) Responsivity at the 250 nm light illumination dependence on the temperature. (c) Time response upon the 250 nm light illumination at various temperatures at 5 V. (d) Spectral response measured at 5 V at different temperatures.