Influence of plasma treatments on the properties of GaN/AlGaN/GaN HEMT structures

We investigated the impact of fluorine and nitrogen plasma treatments on the electronic transport properties of GaN/AlGaN/GaN heterostructures by employing different plasma processes and subsequent annealing in nitrogen atmosphere at 425 °C. It is demonstrated that the plasma treatments affect the 2-dimensional electron gas (2DEG) properties of the HEMT structure resulting in a decrease of the surface potential. In order to understand the physical mechanisms we have undertaken an extensive study of the influence of plasma processing on the 2DEG properties. The electrical properties of the 2DEG are characterized by Hall measurements while X-ray photoelectron spectroscopy (XPS) is used to investigate changes in surface chemical composition. Changes of the DC bias voltage have a strong effect on the mobility presumably by incorporation of fluorine and nitrogen close to the channel. To confirm this assumption, Monte Carlo simulations were carried out, taking into account surface potential and negatively charged fluorine acceptors acting as additional scattering centers within the 2DEG.