Modeling and Electrical Characterization of Ohmic Contacts on n-type GaN

As the current requirements of power devices are moving towards high frequency, high efficiency and high-power density, Silicon-based devices are reaching its limits which are instigating the need to move towards new materials. Gallium Nitride (GaN) has the potential to meet the growing demands due to the wide band-gap nature which leads to various enhanced material properties like, higher operational temperature, smaller dimensions, faster operation and efficient performance. The metal contacts on semiconductors are essential as the interface properties affect the semiconductor performance and device operation. The low resistance ohmic contacts for n-GaN have been well established while most p-GaN devices have still high contact resistivity. Significant work has not been found that focuses on software-based modeling of the device to analyze the contact resistance and implement methods to reduce the contact resistivity. Understanding the interface physics in n-GaN devices using simulations can help in understanding the contacts on p-GaN and eventually reduce its metal contact resistivity. In this work, modeling of the metal-semiconductor interface along with the effect of a heavily doped layer under the metal contact is presented. The extent of reduction in contact resistivity due to different doping and thickness of n ++ layer is presented with simulations. These results have been verified by the growth of device based on simulation results and reduction in contact resistivity has been observed. The effect of different TLM pattern along with different annealing conditions is presented in the work. Modeling and Electrical Characterization of Ohmic Contacts on n-type GaN Sai Rama Usha Ayyagari GENERAL AUDIENCE ABSTRACT Technology has become part and parcel of the life of humans which is slowing gearing towards Automation, Internet of Things (IoT). The hardware for this is being provided by semiconductor silicon for a very long time. However, the demand is moving towards smaller size and better performance. Silicon material has reached its limitations in terms of dimension scaling and performance enhancement. A quest for new material has led to Gallium Nitride (GaN) which has the potential to provide enhanced properties like higher operational temperature, smaller dimensions, faster operation and efficient performance. Metal contact on the semiconductor is essential as these contacts provide the external connection. The contact characteristic of the metal-semiconductor interface is evaluated by contact resistance. It is expected that contact has linear IV characteristics (ohmic contact) and low contact resistance to avoid perturbing the semiconductor performance in devices. There are metals which can provide ohmic contacts for n-GaN but they offer low contact resistance only on annealing. These contact characteristics are studied by simulating the metalsemiconductor interface by replicating the thermionic and tunneling effects at the junction by physics-based device modeling. It is essential to reduce the contact resistivity for better interface properties which can be provided by a heavily doped (n ++ ) layer under the metal layer. The effect of various doping and thickness of n ++ layer is presented in this research work. Devices were grown based on simulation results and the extent of reduction in contact resistivity due to the n ++ layer is documented in this research. This reduction in contact resistivity can aid in a significant reduction in power dissipation in the devices which could lead to efficient device operation.