Transistors based on gallium nitride (GaN), growth techniques, and nanostructures
Gallium nitride(GaN) is a material with a wide and straight band gap of 3.39eV. This semiconductor has the crystal structure of Wurtzite as one of the most stable phases of matter in environmental conditions. This material and its alloys have a low intrinsic charge carrier density due to their wide band gap, but on the other hand, they have significant charge transfer properties. These include high electron mobility of about 1300cm2/Vs and usability in high-temperature applications due to its very high thermal conductivity. They also have a saturation velocity of about 2.5*107cm/S and a high breakdown electric field of about 3.5MV/cm compared to 0.3MV/cm for silicon. This paper discussed about the most important GaN crystal growth methods, such as Ammonothermal, Hydride Vapor Phase Epitaxy(HVPE), Sodium flux(Na-flux), Metal-Organic Chemical Vapor Deposition(MOCVD) and Molecular Beam Epitaxy(MBE). Each of these methods has its own advantages and drawbacks and is used in research and industrial fields. MOCVD and MBE techniques are more widely used than other techniques, and due to larger throughput and larger wafer size, MOCVD, is widely used in industrial applications. According to the articles, which were discussed in this paper, countries such as the United States, Japan, and Germany, among other countries, have focused more on these two methods. The most common nanostructures obtained from the studied methods are nanowires, quantum wells, quantum wires, quantum dots, and GaN nanoparticles. This paper mentioned that nanowires and quantum wells are the most widely used morphologies in the structure of GaN-based transistors. Over the past few years, countries such as the United States, South Korea, India, China, and Germany have focused more on the growth of widely used GaN nanostructures.