Gallium nitride based heterojunction field effect transistor: fabrication and application

Abstract

Gallium nitride (GaN) is a wide bandgap semiconducting material, which is piezoelectric, biocompatible, and also resistive to ionizing radiation. Material properties such as direct bandgap, chemical/thermal stability, higher mobility, higher saturation velocity, and higher sensitivity makes it an auspicious material for the use in electronics, optoelectronics as well as bioelectronics based applications. In the first part of this dissertation, fabrication of aluminum gallium nitride/gallium nitride heterojunction field effect transistor (AlGaN/GaN HFET) for the detection of the DNA hybridization has been discussed. Photopatternable spin-on silicone has used to encapsulate the device except the gate electrode for the use in aqueous environment. Biofunctionalization and immobilization chemistry using the assembly of an alkanethiol self assembled monolayer (SAM) onto the metal gate, and the subsequent coupling of amine-terminated ssDNA to the SAM has been discussed. Current-voltage (ID-VDS) and current-time (ID-t) measurements of DNA binding experiments using the field effect transistors are presented, in which the hybridization of a fully complementary target DNA sequence is compared to that of a partly mismatched target DNA sequence. Second part of this dissertation describes the incorporation of amorphous lead zirconium titanate (PZT) thin film as a gate dielectric in AlGaN/GaN heterojunction field effect transistor. Comparative study regarding transistor output, transfer and gate current leakage between the Ni/Au Schottky gate conventional HFET and amorphous PZT incorporated PZT/Ni/Au gate HFET were carried out. Significant reduction in gate leakage current had observed with the incorporation of the PZT thin film as a gate dielectric.