Organic Molecular Surface Modification of III-Nitride Wide Bandgap Semiconductors for Improved Electronics

Gallium Nitride (GaN) wide band gap semiconductor remains one of the most promising candidates for high-power, high-voltage and radio-frequency electronic technologies and opto-electronic devices owing to its superior material properties and stability in harsh environments. The ability of GaN to form heterostructures with one of its alloy compounds, AlGaN, allows the fabrication of high electron mobility transistors (HEMTs) which are now replacing other conventional devices such as JFET and MOSFETs. Also, due to the wider bandgap of 3.4 eV and photoconductive properties, GaN is also suitable material for detecting Ultraviolet (UV) radiations. In spite of a large number of efforts for the development of these devices, there are still some issues which need to be resolved to utilize the full potential of GaN technology. One of the issues which affect the device properties is the development of defect states (due to point defects and dislocations) and electronic gap states or trap states at the surface of the semiconductor. These defects and surface states adversely affect the performance of metal contacts thereon, especially the Schottky metal-semiconductor (MS) contacts. A few effects are seen in the form of Fermi Level pinning, Schottky barrier lowering, Schottky barrier inhomogeneity, carrier tunnelling across the MS interface and large reverse bias leakage current. In order to overcome some of these device-efficiency-degrading effects, we present a unique surface modification process of GaN based epitaxial films and AlGaN/GaN based heterostructures by adsorption of a single layer of specifically structured organic molecules. The detailed analyses of different experimental characterizations have revealed that by this process, the surface electrical properties of the semiconductors (GaN and AlGaN/GaN) get tuned. This further improves the electrical characteristics of the Schottky diodes and hence enhances the performance of both electronic and opto-electronic devices.