Abstract
This study presents an innovative, low-cost, mass-manufacturable ion implantation technique for converting thin film normally on AlGaN/GaN devices into normally off ones. Through TCAD (Technology Computer-Aided Design) simulations, we converted a calibrated normally on transistor into a normally off AlGaN/GaN transistor grown on a silicon <111> substrate using a nitrogen ion implantation energy of 300 keV, which shifted the bandgap from below to above the Fermi level. In addition, the threshold voltage (Vth) was adjusted by altering the nitrogen ion implantation dose. The normally off AlGaN/GaN device exhibited a breakdown voltage of 127.4 V at room temperature because of impact ionization, which showed a positive temperature coefficient of 3 × 10−3 K−1. In this study, the normally off AlGaN/GaN device exhibited an average drain current gain of 45.3%, which was confirmed through an analysis of transfer characteristics by changing the gate-to-source ramping. Accordingly, the proposed technique enabled the successful simulation of a 100-µm-wide device that can generate a saturation drain current of 1.4 A/mm at a gate-to-source voltage of 4 V, with a mobility of 1487 cm2V−1s−1. The advantages of the proposed technique are summarized herein in terms of processing and performance.
Highlights
Silicon power transistors have been developed for decades but have recently started facing physical limits in terms of mobility, high-voltage, and high frequency, preventing further major advancements [1]
Gallium nitride (GaN) transistors, which are characterized by considerably lower capacitance levels, are only at the infancy stage of development and their lower capacitance levels are due to their superior material and physical properties such as higher conductivity, higher energy gap, and higher electrical field as compared with silicon [2]
We provide an overview of the underlying physical mechanism of the nitrogen ion implantation technique that affords a robust approach for fabricating normally off gallium nitride (GaN) High-Electron-Mobility Transistors (HEMTs)
Summary
Silicon power transistors have been developed for decades but have recently started facing physical limits in terms of mobility, high-voltage, and high frequency, preventing further major advancements [1]. Growing GaN naturally on a silicon substrate results in a normally on or a D-mode device inherently characterized by stress-induced two-dimensional electron gas (2DEG) formation [3]. Gate recess [15], fluorine plasma ion implantation [16], and p-type cap [17] techniques are the commonly used approaches for fabricating normally off High-Electron-Mobility Transistors (HEMTs).
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