Preparation and ultraviolet detection performance of Cu doped <i>β</i>-Ga₂O₃ thin films

Abstract

Solar-blind UV photodetectors (SBPs) have attracted great attention because they are widely used in missile tracking, fire detection, biochemical analysis, astronomical observations, space-to-space communications, etc. At present, it is found that wide bandgap semiconductor materials such as Al_<i>x</i>Ga_1-<i>x</i>N, Mg₁Zn_1-<i>x</i>O, diamond and <i>β</i>-Ga₂O₃ are ideal semiconductor materials for developing high-performance SBPs. The ultra-wide band gap semiconductor material, <i>β</i>-Ga₂O₃, has a large band gap width of 4.9 eV, strong breakdown electric field, absorption edge located in the solar blind ultraviolet band (200–280 nm), and it also has high transmittance in the near ultraviolet and the whole visible band. Therefore, <i>β</i>-Ga₂O₃ is a very suitable material for making solar blind UV photodetectors. However, the p-type <i>β</i>-Ga₂O₃ is difficult to dope, which limits the further development of <i>β</i>-Ga₂O₃ devices. In this work, the <i>β</i>-Ga₂O₃ thin films with different Cu doping content are grown on sapphire substrates by chemical vapor deposition method, and the morphology, crystal structure and optical properties of <i>β</i>-Ga₂O₃ films are measured. The test results show that the surfaces of <i>β</i>-Ga₂O₃ films with different Cu content are relatively smooth, and the (<inline-formula><tex-math id="M2">\begin{document}$ \bar 201 $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20230971_M2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20230971_M2.png"/></alternatives></inline-formula>) diffraction peak positions shift toward the lower degree side with the increase of Cu content, which indicates that Cu²⁺ replaces Ga³⁺ and enters into the <i>β</i>-Ga₂O₃ lattice. The optical absorption spectrum measurement indicates that the energy gaps of samples are evidently narrowed with the increase of Cu doping concentration. Hall measurements indicate that the Cu doped <i>β</i>-Ga₂O₃ thin films have a p-type conductivity with a hole concentration of 7.36 × 10¹⁴, 4.83 × 10¹⁵ and 1.69 × 10¹⁶cm^–3, respectively. In addition, a photoconductive UV detector with metal-semiconductor-metal structure is prepared by evaporating Au on a Cu-doped <i>β</i>-Ga₂O₃ thin film, and its UV detection performance is studied. The results show that the photocurrent value of the device increases with Cu content increasing. The photo-to-dark current ratio (<i>I</i>_l/<i>I</i>_d) is about 3.8×10² of 2.4% Cu content device under 254 nm-wavelength light at 10 V. The rise time and decay time are 0.11 s and 0.13 s, respectively. Furthermore, the responsivity and external quantum efficiency can reach 1.72 A/W and 841% under 254 nm-wavelength light with a light intensity of 64 μW/cm².