Chapter 5 - Gan-Based Modulation-Doped Field-Effect Transistors and Ultraviolet Detectors

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Semiconductor nitrides such as aluminum nitride (AlN), gallium nitride (GaN), and indium nitride (InN) are very promising materials for their potential use in optoelectronic devices and high-power and high-temperature electronic devices. Specifically, nitrides are suitable for applications such as surface acoustic wave (SAW) devices, UV detectors, Bragg reflectors, waveguides, UV and visible light emitting diodes (LED), and laser diodes (LD) for digital data read-write applications. The large bandgap, large dielectric breakdown field, fortuitously good electron transport properties, and good thermal conductivity of GaN are conducive for use in high-power electronic devices. This chapter focuses on GaN based semiconductor devices and there use as modulation-doped field effect transistors (MODFET) and ultraviolet detectors. With its reduced impurity scattering and unique gate capacitance-voltage characteristics, the MODFET has become the dominant high-frequency device. Research has reported on the superior performance of GaN-based MODFET on SiC and sapphire substrates with respect to competing materials, particularly at X band and higher frequencies. The chapter also describes the problem of polarization in GaN semiconductors, highlighting the main reasons. It also discusses topics such as Schottky barriers for gates in GaN, GaN contacts, and AlGaN/GaN MODFETS, focusing on GaN characteristics and experimental performance. UV detector structures based on GaN and AlxGAl-xN include photoconductors (PC), metal semiconductor-metals (MSM), and photovoltaics (PV). These detector structures were typically grown on sapphire substrates by variations of molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD) methods. The chapter closes with a discussion on these properties of GaN based semiconductors and their design and application as UV detectors.