Study On Electrical Characteristics Of (Al) GaN Schottky Diodes

High power Schottky devices are widely applied in power-switching circuits. Currently, performances of the most commercially used Si-based power devices are approaching their physics limits. It is very difficult for them to make new breakthroughs in the high temperature, high frequency and high power aspects, so they are unable to meet the continuously improved practical requirements. As a result, new Ga N-based power devices have received wide and intensive attention. Ga N has many advantages such as wide and direct bandgap, high breakdown electric field and large electron saturation velocity, and thus shows a great potential in making microwave power devices. However, the quality of Schottky contact has an direct impact on the reliability and lifetime of Ga N-based devices. Aiming at the(Al)Ga N Schottky contact, which currently has limited domestic researches, we conduct detailed investigations on the fabrications, electrical characteristics and theoretical models of Ni-Au/Al Ga N/Ga N heterostructure Schottky diodes and Ni-Au/n-Ga N Schottky diodes.Firstly, the fundamental theory of metal-semiconductor contact and the principle of Schottky contact are introduced, as well as the effects of image force and tunneling on Schottky contact. The curent transport mechanisms of Ga N Schottky diodes in the forward and reverse biases are then discussed in emphasis, including the thermionic emission(TE), tunneling current(TU) and Frenkel-Poole(FP) mechanism. The sample testing and analyzing methods, and the parameter extraction method of Ga N Schottky diodes are also introduced, including obtaining the barrier height, ideality factor and series resistance by current-voltage(I-V) and capacitance-voltage(C-V) measurements.Secondly, the Ni-Au/Al Ga N/Ga N heterostructure Schottky diode is fabricated. The electrical characteristics investigations reveal that the carrier transport mechanisms of the Schottky contact are quite complicated. In order to clarify different current transport mechanisms under varied temperatures and biases, the temperature variable I-V characteristics are analyzed by data fitting. The results show that, the forward low-bias current is dominated by the tunneling current, while the forward high-bias current consists mainly of the TE current. The reverse current, on the other hand, is governed by the FP mechanism. In the forward low-bias region, the temperature dependences of characteristic energy and transmission coeffienct are derived based on the characteristics of tunneling current, while in the forward high-bias region, the barrier height is obtained based on the TE model, which is found more close to the theoretical value.Finally, the electrical properties of the fabricated Ni-Au/n-Ga N Schottky diode are measured and analyzed. The forward electrical characteristics of n-Ga N Schottky diodes are mainly studied by temperature variable I-V curves. The room-temperature barrier height obtained in the forward high-bias region is 0.97 e V, which is more close to the theoretical value of the metal-semiconductor contact. Meanwhile, the step-stress tests are adopted to determine the reverse leakage characteristics and the degradation mechanism of the Ga N-based Schottky diode. The results show that, when the reverse voltage exceeds a critical value, the current increases suddenly along with remarkable noise characteristics, and the degradation phenomenon occurs. The electric field characteristics of Ga N-based Schottky diodes are simulated by the TCAD tool Atlas under reverse-bias conditions, and it is found that the electric field may be the main factor causing the degeneration. The current transport mechanisms are finally explored by fitting I-V curves measured at different stress time.As a summary, by fabricating and studying the electrical characteristics of two different Ga N-based Schottky diodes, the current transport mechanisms of Ni-Au/Al Ga N/Ga N and Ni-Au/n-Ga N Schottky contacts have be analyzed, and the reverse degradation characteristics of n-Ga N Schottky diodes are ten TUively explained, which can provide theoretical and experimental guides for improving the quality of Ga N-based Schottky contacts and even the performances of various Ga N-based devices.