Study On AlGaN Ohmic Contact Of High Al Component

Deep ultraviolet LEDs have been widely used in civilian and military fields and have been favored by a large number of researchers in recent years.AlGaN is a commonly used material for the preparation of deep ultraviolet LEDs.The shorter the wavelength,the higher the Al content,and the difficulty in preparing the ohmic contact of the device also increases sharply.High quality ohmic contact is required for high performance devices.Making stable and reliable ohmic contact is one of the keys to the successful application of AlGaN devices.In this paper,the ohmic contact of AlGaN materials with high Al composition is discussed and studied systematically from theory to experiment.The main research contents and achievements are as follows:(1)Theoretically understand the formation mechanism of ohmic contacts,and use the principle of reducing the barrier height of metal-semiconductor contacts and thinning the barrier width to promote the formation of ohmic contacts to design experimental schemes.The dot transmission line model is used to calculate the specific contact resistivity based on factors such as principle calculation,process preparation and result accuracy.(2)By means of XRD,Hall test and transmission spectrum,the quality and characteristics of the material are understood.The detection of XPS shows that there are oxides and organics on the surface of the material,which provides a research direction for the treatment process of the material surface.The preparation process of ohmic contact,such as photolithography,electron beam evaporation and rapid heat annealing,is studied in detail to improve the reliability and repeatability of the process.(3)The metal system with Ti/Al/Ti/Au as the n-type electrode was used to optimize the process parameters such as alloy annealing conditions and metal thickness through a large number of experiments.It was helpful to prepare a good quality ohmic contact.The phase analysis of XRD was used to understand the alloy,and it was concluded that the Al₃Ti compound was helpful for the formation of ohmic contact.Based on this idea,a two-layer Ti/Al superimposed metal structure was set up,and it was found that the more complete reaction of Ti and Al can optimize the quality of ohmic contact.The main processes for preparing ohmic contact include photolithography,electron beam evaporation and rapid heat annealing.(4)The metal system with Ni/Au as the p-type electrode was used to optimize the annealing condition and metal ratio of the alloy.It was found that the ohmic contact quality with Ni/Au metal ratio of 1/1 was the best under the conditions of oxygen atmosphere,600?and 10min.According to the optimized metal ratio,the optimal metal thickness of Ni and Au was explored.The experimental results showed that the specific contact resistivity was the smallest when the Ni/Au thickness was 20/20nm.