Heterostructure concepts for group III-nitrides

• Applicant: Professor Dr.-Ing. Andrei Vescan
• Subject Area: Electronic Semiconductors, Components and Circuits, Integrated Systems, Sensor Technology, Theoretical Electrical Engineering
• Term: from 2010 to 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 167739273

This project is focused on fundamental studies of the growth and the investigation of the electronic properties of quaternary InAlGaN-based heterostructures, aiming at the realization of novel electronic device concepts.Most group III-nitrides field effect transistor concepts are based on the fact that, due to the difference in polarization between barrier layer (usually AlGaN or InAlN) and underlying buffer, a large positive sheet charge is present at the heterointerface. The accumulation of compensating mobile negative charges at this interface leads to the formation of a two-dimensional electron gas. However, the permanent polarization of the typically used ternary barrier layers offers limits the available parameter space for the design of electronic devices. Important device concepts like normally-off or double heterostructure transistors are very difficult to achieve. Using the newly developed quaternary InAlGaN barrier layers, we demonstrated during the first project phase enhancement mode (normally-off) heterostructure field effect transistors (HFET), with performances which promise to reach the levels of conventional depletion-mode devices. The additional degree of freedom enables novel structures for fundamental semiconductor physics studies and also new electronic devices.In the present project we are following this new path aiming to maximize the parameter space which is now available for the design of heterostructure devices. For example multilayer-structures, consisting of several layers with high and low polarization, are being aimed at with the goal of achieving even higher positive threshold voltages in the fabricated transistor and simultaneously optimizing the on-resistance. The challenge will be to understand the properties of the individual layers and to find suitable combinations matched to achieve the desired device performance. By doing this we expect to overcome the limitations of single barrier heterostructures.The parameter space which has been investigated so far has been limited by strain due to the lattice constant of the GaN-buffer used in the previous work. New growth studies on AlN- and AlGaN-buffer layers will enable the fabrication of quaternary barrier layers with compositions not possible till now. The next logical step, transistors with active AlGaN channel may open new avenues towards high-voltage and high-temperature devices.

• DFG Programme: Research Grants