An Overview of Normally-Off GaN-Based High Electron Mobility Transistors

Abstract

Today, the introduction of wide band gap (WBG) semiconductors in power electronics has become mandatory to improve the energy efficiency of devices and modules and to reduce the overall electric power consumption in the world. Due to its excellent properties, gallium nitride (GaN) and related alloys (e.g., AlxGa1−xN) are promising semiconductors for the next generation of high-power and high-frequency devices. However, there are still several technological concerns hindering the complete exploitation of these materials. As an example, high electron mobility transistors (HEMTs) based on AlGaN/GaN heterostructures are inherently normally-on devices. However, normally-off operation is often desired in many power electronics applications. This review paper will give a brief overview on some scientific and technological aspects related to the current normally-off GaN HEMTs technology. A special focus will be put on the p-GaN gate and on the recessed gate hybrid metal insulator semiconductor high electron mobility transistor (MISHEMT), discussing the role of the metal on the p-GaN gate and of the insulator in the recessed MISHEMT region. Finally, the advantages and disadvantages in the processing and performances of the most common technological solutions for normally-off GaN transistors will be summarized.

Design and Simulation of High Performance Lattice Matched Double Barrier Normally Off AlInGaN/GaN HEMTs

“…It is because the achieved high current density and good scalability of AlInGaN barrier can effectively boost the high-frequency performance [29]; moreover, the normally-off operation of the explored double barrier device (i.e. Sample II) is crucial in high-power electronics [2,5].…”

“…Although ornamented by plethora of crucial high performance outcomes, normally-on operation is one of the fundamental limitations of GaN-based HEMTs. This shortcoming limits device characteristics for practical applications [5] because power switching applications demand normally-off transistors to guarantee a safe and low-cost operation in power electronic systems [6]. Various techniques, such as use of recess gate [7], fluoride ion implantation [8], p-type gate material [9] and cascade [10] have been applied to obtain normally-off HEMTs.…”

Current Trends in the Development of Normally-OFF GaN-on-Si Power Transistors and Power Modules: A Review

“…5b). When the thickness of the AlGaN layer is below a certain value, the Fermi energy level shifts down to below the conduction band, thus depleting the 2DEG and the normally-OFF characteristic is achieved 40 and is commonly combined with the MIS HEMT structure to minimize the gate leakage current. The recessed gate provides a high transconductance (g m ), saturation current (I sat ), and BV while suppressing the occurrence of current collapse.…”

Nanotribological Properties of Ga- and N-Faced Bulk Gallium Nitride Surfaces Determined by Nanoscratch Experiments

“…By virtue of its wide forbidden band, direct energy gap, high temperature, and pressure resistance, etc., gallium nitride (GaN) has been widely used in blue/green/ultraviolet light emitting diodes (LEDs) [1,2], high electron mobility transistors [3,4], high power and frequency electronic devices [5,6], and so on. During the processes of preparation, packaging, and transportation of GaN-based devices, e.g., LEDs, a dislocation or defect can be easily produced under the slight stress and creep effect (usually caused by the normal load and frictional force at micro/nanoscale) [7,8], which would lead to the reduction of photoelectric conversion efficiency of LEDs [9].…”