Research On The Growth Of High-quality Aluminum Nitride Films And Its Deep Ultraviolet Photodetectors

In recent years,the research on semiconductor materials with wide bandgap is in full swing.Among them,aluminum nitride(AlN)is a typical ultral-wide bandgap semiconductor material with a bandgap up to 6.2 eV.As a direct bandgap semiconductor material,it has a large absorption coefficient and high efficiency of photoelectric conversion,and its cut-off wavelength is in the solar blind area.Therefore,it has great application potential in the field of deep ultraviolet photoelectricity.However,high-quality AlN is expensive and difficult to mass produce,and the research of related devices is still immature,which limits its application.In this paper,reactive radio frequency magnetron sputtering(RRFMS)and post-annealing technology were used to grow high-quality AlN films at low cost,and then the films were applied to deep ultraviolet photodetectors(DUV-PDs).The main research contents and results are as follows:The as-grown AlN films by RRFMS was investigated.The effects of substrate temperature,radio frequency power,growth pressure and nitrogen content on the crystalline quality of AlN films were investigated.The results show that substrate temperature of 400?,radio frequency power of 250 W and growth pressure of 0.3Pa correspond to the best parameters.Increasing the proportion of nitrogen to the working gas can promote the growth of AlN films along the c-axis preferred orientation,while reduce the lateral size of the crystalline grains.Based on the consideration of high c-axis preferred orientation,the quality of AlN is the best under the condition of 100%nitrogen content.At this condition,the full-width at half maximum(FWHM)of 2?diffraction peak of AlN(0002)plane is 0.18°in XRD pattern,and the FWHM of E₂(high)mode vibrational peak is 20.5 cm^-1 in Raman spectrum.Additionally,the grains in the film are densely and orderly arranged and have columnar structure.However,there are obvious grain boundaries in as-grown films,and the defect density is high,the quality of as-grown films needs to be further improved.The annealing process of AlN films was investigated.Through face-to-face annealing,the effects of annealing temperature and annealing time on the crystallization quality of AlN films were investigated respectively.And high-quality AlN films were obtained through post-annealing process.Under the existing experimental system,1600?and 120 min correspond to the best post-annealing parameters.The post-annealing process facilitates repairing the lattice of AlN,and the FWHM of E₂(high)vibrational peaks in Raman spectra was reduced obviously.The minimum FWHM is only 7.5 cm^-1.Besides,the grains in AlN films fused into films,and the grain boundaries disappeared,indicating that the post-annealing process can greatly improve the crystalline quality of AlN films.DUV-PDs based on AlN films were investigated.By comparing different electrode materials,active region materials and device structures,we can get the following conclusions.(1)Aluminum is more suitable as the electrode material of DUV-PD.(2)Annealed AlN films can significantly improve the responsibility of the detector.Under the irradiation of 189.4 nm light source,the responsibility of the detector with MSM coplanar-electrode structure is up to 0.51 A/W at the bias voltage of 50 V.(3)Under the conditions of existing process,the bifacial-electrode structure can narrow the electrode spacing and increase the intensity of the electric field,and the carriers can be transported along the c-axis nanopillars of AlN,which significantly improves the responsibility of the detector.(4)The DUV-PD based on h BN/AlN heterostructure showed high photoelectric response and good switching repeatability.The deep ultraviolet optoelectronic devices based on this heterostructure have great potential in the future.