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This experiment studied the effects of multi-layer Ti/Al electrodes, ohmic groove etching, and annealing temperature on the ohmic characteristics, output characteristics, and surface topography of AlGaN/GaN high electron mobility transistor (HEMT) devices. In the experiment, we prepared the device structure through the linear transmission model. We then used an atomic force microscope, B1500A, and other instruments to test the output characteristic curve and surface roughness of the device under each temperature and structure. After analysis and calculation, it is found that the device with an etched depth of 10 nm in the ohmic groove of the multi-layer Ti/Al electrode obtains the best characteristics when fast annealed at 850 °C for 30 s. The contact resistance value of the improved device is only 54.3% of that of the traditional structure, and the specific contact resistivity is reduced by 71.8% compared with that of the traditional structure. The surface morphology of the improved device is also smoother, and the surface roughness rms value is only 40.5% of that of the traditional structure. When it is applied to the HEMT device, the output current is increased by 40.7% compared with the traditional structure.
This experiment studied the effects of multi-layer Ti/Al electrodes, ohmic groove etching, and annealing temperature on the ohmic characteristics, output characteristics, and surface topography of AlGaN/GaN high electron mobility transistor (HEMT) devices. In the experiment, we prepared the device structure through the linear transmission model. We then used an atomic force microscope, B1500A, and other instruments to test the output characteristic curve and surface roughness of the device under each temperature and structure. After analysis and calculation, it is found that the device with an etched depth of 10 nm in the ohmic groove of the multi-layer Ti/Al electrode obtains the best characteristics when fast annealed at 850 °C for 30 s. The contact resistance value of the improved device is only 54.3% of that of the traditional structure, and the specific contact resistivity is reduced by 71.8% compared with that of the traditional structure. The surface morphology of the improved device is also smoother, and the surface roughness rms value is only 40.5% of that of the traditional structure. When it is applied to the HEMT device, the output current is increased by 40.7% compared with the traditional structure.
Ohmic contact is directly related to the performance of GaN device and is one of the important factors affecting device performance. In recent years, many research groups have studied the electrode materials and annealing conditions of n-type GaN Ohmic contacts. In this paper, the ohmic contact properties and structural characteristics of the Hf/Al electrode of a transition group metal refractory metal Hf system under different annealing conditions are studied, and compared with those of the Ti-based ohmic contact Ti/Al electrode. The specific contact resistivity of each electrode is measured by a dot-type transmission line model, and the structural characteristics of the electrode are analyzed by using an Auger electron spectrometer which can be analyzed in depth. The results show that the Hf/Al electrode under the same annealing condition exhibits superior ohmic contact performance compared with the conventional Ti/Al electrode. At the same time, the lowest specific contact resistivity of the Hf/Al electrode annealed in an N<sub>2</sub> atmosphere at a low temperature of 650 ℃ for 60 s is 4.28×10<sup>–5</sup> Ω·cm<sup>2</sup>. The in-depth analysis of Auger electron spectrum shows that the Hf/Al electrode has a solid phase reaction with the n-type GaN material. In addition, the cross section of each electrode is observed by auger electron spectroscopy. In the Hf/Al electrode sample, the metal-semiconductor interface does not show voids after annealing. This situation occurs at the sample interface where the Ti/Al electrode is annealed at 650 ℃ for 60 s in N<sub>2</sub> atmosphere and annealed at 850 ℃ for 30 s in N<sub>2</sub> atmosphere. This is one of the reasons why the Hf/Al electrode sample has a lower specific contact resistivity. At the same time, the surface of Hf/Al electrode and Ti/Al electrode annealed at 850 ℃ are characterized by using scanning electron microscope. It is found that the surfaces of both electrodes subject to high temperature annealing show a similar granular rough surface, and this rough surface has a certain influence on the electrical properties of the GaN device. The rough surface formed by the electrode under such high temperature annealing conditions is an urgent problem to be solved in the future research. In summary, the study in this paper indicates the use of Hf/Al to form an ohmic contact with n-type GaN under a low temperature annealing condition.
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