Study On The Processing Of Gan-Based Millimeter/Submillimeter Wave Schottky Barrier Diodes

In recent years,the millimeter-wave and submillimeter-wave devices and modules have been rapidly developed because of their outstanding advantages in modern wireless communication.Schottky diodes have wide applications at this band.Schottky diodes have a mainstream position whether mixers in an IC receiving system or multipliers in a solid state source component.With the development of millimeter-wave and submillimeter-wave technology,high frequency and high power components are needed to meet the increasing demands.It requires to improve both power and cut-off frequency of Schottky diodes.GaN are widely used in a lot of high frequency and high power devices because of its wide band gap and high breakdown voltage features.As one of the representatives of wide bandgap semiconductor devices,GaN-based Schottky diodes have been the focus of people's research.The research on GaN based Schottky diodes mainly focus on two aspects,one is increasing the reverse breakdown voltage and leakage current,and the other is increasing the cut-off frequency.The research of this paper is to improve the cut-off frequency of GaN-based Schottky diodes.The cut-off frequency is inversely proportional to the series resistance and zerobiased capacitance of the Schottky diodes.People usually reduce the anode contact area or increase the Al composition of the AlGaN layer to increase the cut-off frequency.However,this method will be useless with the increasing application's requirement.In this paper,we used a new way to improve the cut-off frequency.The method is to replace the original constant Al composition AlGaN layer with Al composition gradual changed AlGaN layer,which can broaden the potential well near the AlGaN/GaN heterojunction interface.By increasing the high conductance region in the heterojunction,Al-changed AlGaN layer reduces the series resistance,and increases the cut-off frequency of Schottky diodes.This paper's research work has two parts.The first is simulation of Schottky diodes.With the help of software,the Schottky diodes with constant Al composition AlGaN layer and Al composition gradual changed AlGaN layer are simulated to calculate the energy band structure and I-V curve.By comparing the series resistance of these two Schottky diodes,we can confirm that the series resistance of the Al composition gradual changed AlGaN layer structure is lower than constant Al composition AlGaN layer structure.The second is the experimental verification.We have growed the Al composition gradual changed AlGaN layer and constant Al composition AlGaN layer structure wafers.Besides,wo also did HR-XRD,SEM,AFM,Raman spectroscopy and Hall effect test to compare and analysis these two epitaxial wafers.Then,the Schottky diode process is fabricated on them.In order to prevent the parameter of Schottky diodes from the influence of complex structure,we used a large-scaled flat electrode structure with less parasitic parameters and simple structure which could reduce the difficulty of the process.After the diodes was fabricated,I-V and CV tests were performed.The series resistance and zero-biased capacitance were extracted from the test results,and the cut-off frequency was also calculated.The results show that the Schottky diodes with Al composition gradual changed AlGaN layer structure has lower series resistance and higher cut-off frequency.It is verified that the Al composition gradual changed AlGaN layer can improve Schottky diodes' cut-off frequency compared with constant Al composition AlGaN layer structure.Finally,the millimeter-wave and submillimeter-wave bands GaN-based Schottky diodes flow chip experiment was carried out on Al composition gradual changed AlGaN layer heterojunction and constant Al composition AlGaN layer heterojunction,the detailed layout was designed and the flow test results were summarized.