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

Abstract

A Solar-blind UV photodetectors (SBPs) have been attracting great attention due to their widely used in missile tracking, fire detection, biochemical analysis, astronomical observations, space-to-space communications, etc. At present, scholars are found that wide bandgap semiconductor materials such as Al&lt;sub&gt;x&lt;/sub&gt;Ga&lt;sub&gt;1-x&lt;/sub&gt;N, Mg&lt;sub&gt;1&lt;/sub&gt;Zn&lt;sub&gt;1-x&lt;/sub&gt;O, diamond and β-Ga&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;are ideal semiconductor materials for developing high-performance SBPs. As the ultra-wide band gap semiconductor material, β-Ga&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;has the 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 has high transmittance in the near ultraviolet and the whole visible band. Therefore, β-Ga&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; is a very suitable material for making solar blind UV photodetectors. However, the p-type β-Ga&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; is difficult to doping, which limits the further development of β-Ga&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; devices. In this paper, the β-Ga&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; thin films with different Cu doping contents were grown on sapphire substrates by chemical vapor deposition method, and the morphology, crystal structure and optical properties of β-Ga&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; films were measured. The test results show that the surface of β-Ga&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; films with different Cu contents is relatively smooth, and the (-201) diffraction peak positions shift to the lower degree side with increasing Cu content, which indicates that Cu&lt;sup&gt;2+&lt;/sup&gt; is substituted for Ga&lt;sup&gt;3+&lt;/sup&gt; into the β-Ga&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; lattice. The optical absorption spectrum measurement indicated that the energy gaps of samples were evidently narrowed with increasing Cu doping concentration. Hall measurements results indicated that the Cu doped β-Ga&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; thin films was p-type conductivity with a hole concentration of 7.36×10&lt;sup&gt;14&lt;/sup&gt;, 4.83×10&lt;sup&gt;15&lt;/sup&gt; and 1.69×10&lt;sup&gt;16&lt;/sup&gt; cm&lt;sup&gt;−3&lt;/sup&gt;, respectively. In addition, a photoconductive UV detector with MSM structure was prepared by evaporation of Au on a Cu-doped β-Ga&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;thin film, and its UV detection performance was studied. The results show that the photocurrent value of the devices increases with the increasing Cu contents. The &lt;i&gt;I&lt;/i&gt;&lt;sub&gt;l&lt;/sub&gt;/&lt;i&gt;I&lt;/i&gt;&lt;sub&gt;d&lt;/sub&gt; ratio is about 3.8×10&lt;sup&gt;2&lt;/sup&gt; of 2.4% Cu content device under 254 nm light with at 10 V. The rise time and decay time of 0.11 s and 0.13 s, respectively. Furthermore, the responsivity and external quantum efficiency can reach up to 1.72 A/W and 841% under 254 nm light with a light intensity of 64 μW/cm&lt;sup&gt;2&lt;/sup&gt;.