Publication

Leakage mechanisms and contact technologies in InAlN/GaN high electron mobility transistors

Lorenzo Lugani
2015
Theses

Abstract

GaN based electronic devices have progressed rapidly over the past decades and are nowadays starting to replace Si and classical III-V semiconductors in power electronics systems and high power RF amplifiers. AlGaN/GaN heterostructures have been, until recently, the materials system of choice for nitride based electronics. The limits of AlGaN/GaN technologies are now known and alternative routes able to overcome them are actively investigated. Nearly lattice-matched InAlN/GaN heterostructures have emerged as viable solutions for extending the frequency range achievable by GaN based devices. These heterostructures have also proven a very high thermal stability, becoming of high interest for extreme environment applications. However, despite those great potentials, InAlN/GaN based devices, in particular high electron mobility transistors, have suffered from high leakage currents, strong short channel effects and low breakdown voltage that made them not competitive with respect to AlGaN/GaN technologies. The goal of this thesis is to investigate, understand and control the mechanisms that limit the performance of InAlN/GaN based transistors. Particular attention in this thesis will be given to leakage currents, having gate or buffer origin. Concerning gate leakage currents, an accurate model for InAlN/GaN heterostructures will be established and the expected presence of deep levels will be confirmed by means of photocapacitance spectroscopy. Based on these results, it will be shown that two conduction mechanisms contribute to gate leakage currents. A first mechanism dominates in heterostructures with thin (

Official source

Lorenzo Lugani
2015
Theses

Abstract

Official source

Ontological neighbourhood

Physics

Condensed matter physics: Solid-state physics

Related concepts (32)

Transistor

A transistor is a semiconductor device used to amplify or switch electrical signals and power. It is one of the basic building blocks of modern electronics. It is composed of semiconductor material, usually with at least three terminals for connection to an electronic circuit. A voltage or current applied to one pair of the transistor's terminals controls the current through another pair of terminals. Because the controlled (output) power can be higher than the controlling (input) power, a transistor can amplify a signal.

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Gallium nitride () is a binary III/V direct bandgap semiconductor commonly used in blue light-emitting diodes since the 1990s. The compound is a very hard material that has a Wurtzite crystal structure. Its wide band gap of 3.4 eV affords it special properties for applications in optoelectronic, high-power and high-frequency devices. For example, GaN is the substrate which makes violet (405 nm) laser diodes possible, without requiring nonlinear optical frequency-doubling.

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A high-electron-mobility transistor (HEMT or HEM FET), also known as heterostructure FET (HFET) or modulation-doped FET (MODFET), is a field-effect transistor incorporating a junction between two materials with different band gaps (i.e. a heterojunction) as the channel instead of a doped region (as is generally the case for a MOSFET). A commonly used material combination is GaAs with AlGaAs, though there is wide variation, dependent on the application of the device.

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