Abstract
AlGaN/GaN-Si based MIS-HEMTs are considered as the popular candidates for application in the 5G communication system due to their competitive characteristics and low cost. Ohmic contact, as an important fabrication process, significantly affects the performance of the device. In this study, the ohmic contact process, including the SiN passivation layer etching, surface treatment, and barrier layer etching, was studied in detail in order to effectively optimize the device performance. It is observed that the sample with the SiN passivation layer etched by the magnetic neutral loop discharge (NLD) resulted in a lower contact resistance as compared to the reaction ion etching (RIE). The sample surface treated with the O plasma and pickled in the HCl:H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O = 1:10 liquid could effectively remove the pollutants and oxides from the surface, thus, correspondingly presenting a lower ohmic contact resistance as compared to the N2 plasma. Meanwhile, an optimum etching depth was developed with the ICP process for 6 min with an etching speed of 1.6 nm/min. A contact resistance of 0.76 Ω · mm and square resistance of 274.63 ohm/sq were observed under the above-mentioned optimized ohmic contact process. The AlGaN/GaN-Si MIS-HEMT with gate length of 0.5 μm, gate-source space of 1 μm, gate-drain space of 2.5 μm, and gate width of 100 μm was fabricated using the optimized process. A saturation current density of 794.30 mA/mm and the maximum transconductance of 16.86 mS were observed. The findings in this study provide the experimental basis for the manufacturing of AlGaN/GaN-Si based MIS-HEMTs for RF applications.
Highlights
Compared with the traditional III-V compounds of the GaAs and InP materials, the GaN material presents excellent characteristics, e.g., large bandgap width, high breakdown electric field, optimal thermal conductivity, high-temperature resistance, and effective radiation resistance
The gate leakage current seriously affects the efficiency of the GaN-Si high electron mobility transistors (HEMTs) for RF application
For SiN passivation etching, the sample processed with the neutral loop discharge (NLD) method had a smaller contact resistance due to the lower surface damage and higher uniformity as compared to the reaction ion etching (RIE) process
Summary
Compared with the traditional III-V compounds of the GaAs and InP materials, the GaN material presents excellent characteristics, e.g., large bandgap width, high breakdown electric field, optimal thermal conductivity, high-temperature resistance, and effective radiation resistance. A thin film of insulator layer is deposited on the surface of the GaN epitaxy in order to form the metal-insulator-semiconductor (MIS) gate structure to effectively suppress the gate leakage current [2], [3]. For this reason, GaN-Si MIS-HEMTs are observed to be the most promising devices in RF application, especially for the upcoming 5G communication system [4], [5]. This study analyzes the ohmic contact process conditions of GaNSi HEMTs in detail, such as SiN passivation etching, surface treatment, and barrier layer etching, in order to determine an optimized combination of these aspects for improving the ohmic contact performance of AlGaN/GaN-Si MIS-HEMTs
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