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The oxidation mechanism in self-terminating wet etching technique with thermal oxidation of AlGaN layer followed by etching in KOH solution is investigated. Spike-shape remnants of oxidised AlGaN are observed at the initial stage of wet etching in KOH solution, which could be completely etched away after enough etching time. Transmission electron microscope/energy dispersive spectroscopy analysis indicates the existence of crystalline AlGaN inside the remnants. Finally, a possible explanation is given that the oxide channels from AlGaN surface towards AlGaN/GaN interface generated during thermal oxidation are firstly etched away at the initial stage of KOH wet etching, then after enough time these remnants with non-c axis crystal orientation surfaces exposed to KOH solution could be completely etched away leaving GaN layer beneath unaffected, which realises self-terminating etching. [ABSTRACT FROM AUTHOR]

A self-terminating gate recess wet etching technique with thermal oxidation of the AlGaN/GaN layer followed by etching in potassium hydroxide (KOH) solution was recently proposed by the present authors for normally-off AlGaN/GaN metal-oxide semiconductor field effect transistors (MOSFETs). In this present reported work, the oxidation process inside the AlGaN/GaN heterostructure involved in this technique was analysed using several material characterisation methods. The measurement results show that the concentration and depth of the O element distribution increase with increased thermal oxidation temperature. It is worth noting that after 650°C oxidation almost no O element could be found in the GaN layer and the O element mainly locates in the AlGaN layer with an obvious correlation between the distribution of Al and O elements, where the Al(Ga)-oxide was detected by X-ray photoelectron spectroscopy, which could be etched by 70°C KOH. Thus, self-terminating wet etching on the AlGaN/GaN material is achieved. [ABSTRACT FROM AUTHOR]

300°C operation of a normally-off AlGaN/GaN metal-oxide semiconductor field-effect transistor (MOSFET) is successfully demonstrated, which is fabricated using a self-terminating gate recess etching technique. At 300°C, by employing a 15 nm-thick Al2O3 as the gate dielectric deposited by atomic layer deposition, the fabricated normally-off MOSFET exhibits a threshold voltage (Vth) of 3.2 V, a low off-state leakage current of ~10-7 A/mm and a low forward gate leakage current of ~10-7 A/mm. Thus, a high on/off current ratio of ~ 106 is obtained. Furthermore, the normally-off MOSFET also exhibits small variations in terms of its Vth from room temperature to 300°C with a maximum relative variation of 6.7% in a such temperature range. These results make this normally-off AlGaN/GaN MOSFET very promising for high-temperature digital electronics. [ABSTRACT FROM AUTHOR]