A Study Of Breakdown Voltage And Gate Leakage Current Of AlGaN/GaN HEMT With Field Plate

Gallium nitride material has superior physical properties, such as wide bandgap, high breakdown field, high saturation electron drift velocity and high thermal conductivity, compared to the first and the second generation semiconductor. As a representative of GaN based device, AlGaN/GaN HEMT will have a wide application prospect in high power microwave fields after the device reliability and breakdown voltage improved. The field plate technology is considered to suppress the current collapse and improve the device breakdown voltage greatly, so the field plate structure is being concerned by more and more researchers. In this paper, simulation and experimental measurement were used to study the two key parameters, the field plate length and the thickness of passivation layer.In this paper, firstly, three kinds of device structures were designed. The devices with the field plate lengths 0.2um or lum, the thickness of passivation layer 60nm or 120nm have the common basic parameters which the gate length, the source-drain distance and the gate-drain distance is 0.8um,8.8um and 4um. With the drain voltage 70V or 100V, we observed the peak electric field under the gate and got the results. As the field plate distance increasing from 0.2um to lum, the peak electric field under the gate decreased 15%. As the thickness of passivation layer increasing from 60nm to 120nm, the peak electric field under the gate decreased 10%. It is conclude that the increasing of the field plate length contributes to reduce the peak electric field and improve of the breakdown voltage in a certain ranging. When the thickness of passivation layer exceeds 60nm.the breakdown voltage will decrease.Secondly, the devices with the structures mentioned in former were made in our experiments. In the breakdown voltage measurement, the drain current was limited to 1mA/mm and we observed the breakdown voltage of the device in different field plate structure. The result is:as the field plate distance increasing from 0.2um to 1um, the breakdown voltage improves 14%; as the thickness of passivation layer increasing from 60nm to 120nm, the breakdown voltage decreases clearly. At the same time, the off-state leakage current of the devices was analyzed in this paper. We knew the reason for the low-breakdown was the large gate current.At last, the relationship of the gate leakage current and breakdown voltage with the F plasma treatment condition was discussed in the paper. With the treating power increasing from OW to 150W, the forward leakage current at the positive bias increases from 10-10A to 10-8A.It is concluded that it is easy to form surface defects and trap assisted tunneling by the high power F plasma treating the AlGaN surface which is not conducive to the improvement of the breakdown voltage.