Fabrication And Performance Study Of Mixed Phase (In_xGa_1-x)₂O₃ Thin Film Solar-blind Photodetector

In recent years,with the deep understanding of the solar-blind ultraviolet band（200-280 nm）,its applicability has gradually received attention,including in the military and civil fields such as flame warning,missile detection,medical analysis,digital imaging,etc.This also leads to the vigorous development of solar-blind ultraviolet band photodetector.The working mechanism of a solar-blind ultraviolet photodetector（PD）is to convert the light signal into an electrical signal for qualitative or quantitative monitoring.Ultrawide band gap semiconductors are considered to be the preferred materials for the preparation of solar-blind PD.The ultrawide band gap corresponds to the absorption edge located in the solar-blind ultraviolet band,which can avoid interference caused by absorption signals from other bands.Among them,gallium oxide has～4.9 eV ultra-wide band gap,many crystal structures,large dielectric constant,high breakdown field strength,excellent chemical and thermal stability,and is one of the ideal materials for the preparation of the solar-blind PD.Due to the fact that ternary compounds can improve the stability of materials,increase their versatility,and extend their service life,the(In_xGa_1-x)₂O₃（0<x<1）mixed-phase film similar to Mg_xZn_1-xO and Al_xGa_1-xN ternary compound semiconductors was prepared,and then the Metal-Semiconductor-Metal（MSM）structured photoconductive solar-blind photodetector was prepared based on this film.To further improve the performance,annealing and lattice mismatch reduction were performed.The specific research contents are as follows:（1）(In_xGa_1-x)₂O₃ thin film preparation and characterization:In this paper,chemical vapor deposition（CVD）was used to fabricate(In_xGa_1-x)₂O₃ thin films on a quartz substrate,argon（Ar）as the carrier gas,oxygen（O₂）as reaction gas at 1080℃.The morphology,composition,structure,optical properties,and electrical properties of(In_xGa_1-x)₂O₃ thin films were analyzed.The results show that(In_xGa_1-x)₂O₃ mixed-phase films with different Ga:In atomic ratios have been prepared.In addition,the(In_xGa_1-x)₂O₃ mixed-phase films at all ratios are in ohmic contact with the golden interdigital electrodes.The high-quality,different proportions(In_xGa_1-x)₂O₃ mixed-phase thin films prepared in this chapter lay a good foundation for subsequent device preparation and further optimization.（2）(In_xGa_1-x)₂O₃ mixed-phase thin film solar-blind ultraviolet photodetector construction and optimization:Preparation of MSM structure ultraviolet photodetector based on different Ga:In atom ratio(In_xGa_1-x)₂O₃ mixed-phase thin film.Comparisons show that the optimum device dark current is as low as 10^-12A,due to the grain boundary between In₂O₃ and Ga₂O₃capturing electrons to form barriers that impede electron transport.In order to improve the performance of(In_xGa_1-x)₂O₃ mixed-phase film PD,post-annealing was studied.The device responsiveness is 1000 times higher than that of the unannealed device,but the recovery time is longer due to the higher oxygen vacancy concentration in the(In_xGa_1-x)₂O₃ mixed-phase film after air annealing.（3）Preparation and performance test of solar-blind ultraviolet photodetector based on the(In_xGa_1-x)₂O₃ mixed-phase film grow on sapphire substrate:We substituted quartz substrate for c-Al₂O₃ substrate with a smaller lattice mismatch,and found that Ga₂O₃ in the film grows along the（-201）orientation,which greatly improves the quality of the film.The samples with the higher In₂O₃ content in the precursor also grow In₂O₃ micron lines.Optimal performance(In_xGa_1-x)₂O₃ mixed film（In:6.27 at%）photodetector shows an ultralow dark current of0.2 p A and a large I_{254 nm}/I_dark up to 4.27×10⁶,with a prominent responsivity（1 A/W,254 nm）and a remarkable detectivity(4.62×10¹⁴ Jones)under 10 V bias.And it also shows a high internal gain（488.83%）and faster response（response time:2.81 s;recovery time:0.26 s）.All properties are significantly better than those of devices on quartz substrates,which is attributed to the greatly improved film growth quality after reducing the lattice mismatch on the substrates.In summary,it can be seen that(In_xGa_1-x)₂O₃ material has great potential and research value in the field of ultraviolet photodetection.