AlGaN/GaN High Electron Mobility Transistors (HEMTs) are emerging as next-generation semiconductors optimized for high-power and high-frequency applications, with their performance highly dependent on the surface and interface quality of the AlGaN/GaN structure. In particular, the 2-Dimensional Electron Gas (2DEG) formed in the AlGaN layer is susceptible to trapping by surface defects, which degrades electrical characteristics and makes the device vulnerable to degradation. In this study, we propose an approach to enhance device reliability and performance by forming a gallium oxynitride (GaON) interfacial layer through O₂ plasma treatment on the AlGaN surface. This method effectively suppresses interface defects, resulting in improved electrical properties such as reduced interface trap density (Dit), threshold voltage (Vth) shift, increased drain current density (Id), and enhanced transconductance density (gm). Furthermore, this surface treatment demonstrates the potential for process simplification by improving the electrical characteristics of power semiconductor devices without the need for complex deposition steps.

In this study, we fabricated a metamorphic high-electron-mobility transistor (mHEMT) device with a T-type gate structure for the implementation of W-band monolithic microwave integrated circuits (MMICs) and investigated its characteristics. To fabricate the mHEMT device, a recess process for etching of its Schottky layer was applied before gate metal deposition, and an e-beam lithography using a triple photoresist film for the T-gate structure was employed. We measured DC and RF characteristics of the fabricated device to verify the characteristics that can be used in W-band MMIC design. The mHEMT device exhibited DC characteristics such as a drain current density of 747 mA/mm, maximum transconductance of 1.354 S/mm, and pinch-off voltage of -0.42 V. Concerning the frequency characteristics, the device showed a cutoff frequency of 215 GHz and maximum oscillation frequency of 260 GHz, which provide sufficient performance for W-band MMIC design and fabrication. In addition, active and passive modeling was performed and its accuracy was evaluated by comparing the measured results. The developed mHEMT and device models could be used for the fabrication of W-band MMICs.

In this study, a patterning method using self-aligned nanostructures was introduced to fabricate GaN-based fin-gate HEMTs with normally-off operation, as opposed to high-cost, low-productivity e-beam lithography. The honeycomb-shaped fin-gate channel width is approximately 40~50 nm, which is manufactured with a fine width using a proposed method to obtain sufficient fringing field effect. As a result, the threshold voltage of the fabricated device is 0.6 V, and the maximum normalized drain current and transconductance of Gm are 136.4 mA/mm and 99.4 mS/mm, respectively. The fabricated devices exhibit a smaller sub-threshold swing and higher Gm peak compared to conventional planar devices, due to the fin structure of the honeycomb channel.

Surface passivation of AlGaN/GaN heterojunction structure was examined through the thermal oxidation of evaporated Al. The Al-oxide passivation increased channel conductance of two dimensional electron gas (2DEG) on the AlGaN/GaN interface. The sheet resistance of 463 ohm/□ for 2DEG channel before Al2O3 passivation was decreased to 417 ohm/□ after passivation. The oxidation of Al induces tensile stress to the AlGaN/GaN structure and the stress seemed to enhance the sheet carrier density of the 2DEG channel. In addition, the Al2O3 films formed by thermal oxidation of Al suppressed thermal deterioration by the high temperature annealing.

Citations

• Anomaly and defects characterization by I-V and current deep level transient spectroscopy of Al0.25Ga0.75N/GaN/SiC high electron-mobility transistors
  Salah Saadaoui, Mohamed Mongi Ben Salem, Malek Gassoumi, Hassen Maaref, Christophe Gaquière
  Journal of Applied Physics.2012;[Epub]     CrossRef