Channel Field Effect Transistors

Overview

The document is a final technical report on Ideal Channel Field Effect Transistors (FETs) prepared for the Office of Naval Research by Huili (Grace) Xing from the University of Notre Dame. It covers research conducted from July 24, 2007, to March 31, 2009, focusing on the integration of narrow and wide bandgap semiconductors to enhance the performance of electronic devices.

The report highlights the advantages of narrow bandgap semiconductors, such as high carrier mobilities and low contact resistances, alongside the benefits of wide bandgap semiconductors, which include high breakdown voltages. The research specifically addresses the challenges posed by lattice mismatches between materials, particularly between GaN (gallium nitride) and narrow bandgap semiconductors like InGaN (indium gallium nitride). The significant lattice mismatch complicates the pseudomorphic growth of these materials, which is essential for optimal device performance.

To overcome these challenges, the report explores the technique of direct wafer bonding, also known as wafer fusion. This method allows for the integration of extremely mismatched materials, enabling the fabrication of composite channel transistors. The report details the experimental formation of lattice-mismatched heterostructures, specifically GaAs (gallium arsenide) bonded to GaN. The wafer fusion process involves cleaning the surfaces of the wafers, removing native oxides, and applying pressure and heat to achieve a strong bond while maintaining the crystallinity of the materials.

The findings indicate that the integration of GaAs with GaN through wafer fusion results in dislocation-free structures, which is crucial for improving device performance. The report also discusses the electrical characteristics of the fabricated diodes, noting improvements in breakdown voltage when using GaN compared to traditional GaAs homojunctions. The measured breakdown voltage of GaAs/GaN heterostructures was found to be lower than theoretical predictions, attributed to interface defects.

Overall, the report emphasizes the feasibility of using direct wafer bonding to create high-performance transistors from mismatched semiconductor materials, paving the way for advancements in electronic devices that leverage the strengths of both narrow and wide bandgap semiconductors. Further experiments are suggested to better understand the effects of the interface between these mismatched materials.