Fe Bulk Doping Related Current Collapse Phenomenon

ganfetex10.in : Fe Bulk Doping Related Current Collapse Phenomenon

Requires: Blaze
Minimum Versions: Atlas 5.28.1.R

This example demonstrates simulation of the "Current Collapse" and "Current Recovery" phenomenon resulting from population and de-population of Intentional Iron (Fe) Doping Traps under the gate of a GaN FET as a result of Gate to Drain Electric Fields.

Many publications suggest that un-intentional surface traps are the main cause of the GaN current collapse phenomenon. In this example, we show that sometimes this is not actually the case. Current collapse in this device, is mostly caused by intentional iron doping, whose main purpose is to create a semi-insulating buried layer to reduce the buried layer source to drain leakage path.

The device structure in this example is based on work by Daniel Balaz from his PhD Thesis from University of Glasgow in 2011 entitled "Current collapse and device degradation in AlGaN/GaN heterostructure field effect transistors"

The structure is created using Atlas syntax and the spontaneous and piezo- electric charge concentrations are automatically calculated using the "substrate, polarization and calc.strain" parameters in the region statements.

Substrate leakage current is controlled by a graduated concentration of deep level iron acceptor traps located 1eV below the conduction band edge using the doping statement and the key parameter "trap".

The device is first biased with zero volts on the gate and 5 volts on the drain. After 1 mili-second at this bias, the device is field stressed for only one further milli-second at 25 volts on the drain and -4 volts on the gate. After this short bias stress, the device was returned to it's original bias of zero volts on the gate and 5 volts on the drain. After only one milli-second of bias stress, the drain current is significantly reduced demonstrating the currnet collapse phenomenon.

A comparason structure file plot of the pre and post stress ionized Fe trap density, shows the cause of the current collapse is actually the change in charge state of the Fe doping deep in the substrate under the gate and also on the drain side between the gate and drain contacts.

For completeness, the unstressed bias remained on the device until the traps became de-populated with electrons and the drain current returned to it's original value. Interestingly, it takes over one week for the device to recover ! (6e5 seconds). This very long recovery time may be incorrectly interpreted as device degredation from field induced traps which is an irreversible effect resulting from electric field induced reverse piezo-electric stress.

To load and run this example, select the Load button in DeckBuild > Examples. This will copy the input file and any support files to your current working directory. Select the Run button in DeckBuild to execute the example.