To gain a flat recess profile with uniform etching depth, dry recess experiment with different inductively coupled plasma (ICP) etching conditions was done on an AlGaN/GaN heterostructure. Trenching effect at the bottom near the sidewall was observed when positive photoresist was utilized and the ICP power was low. The recess profile was improved by adopting SiO2 as the etching mask and increasing the ICP power. GaN metal–oxide–semiconductor field-effect transistors (MOSFETs) on AlGaN/GaN heterostructure with different gate recess conditions were fabricated and characterized. The maximum field-effect mobility of 152.8 cm-2 V-1 s-1 and the minimum interface state density of 1.39×1011 cm-2 eV-1 were obtained from the optimized gate recess condition with ICP power of 100 W, bias power of 20 W and etching mask of SiO2.
We report the investigation of boron ion implantation as a device field isolation process for GaN metal-oxide-semiconductor field-effect transistors (MOSFETs) on AlGaN/GaN heterostructure. In the mesa isolation region of a bar-type MOSFET, a parasitic MOS-channel existed and widened the designed channel width, which would result in an overestimated mobility compared with a ring-type MOSFET. After boron ions implantation in the isolation region, the overestimation of field-effect mobility of bar-type MOSFETs was eliminated. The sub-threshold characteristics and on-state drain current of the bar-type MOSFETs coincide with the ring-type devices. Long-channel ring-type MOSFETs, with and without ion implantation, were fabricated on the recess region to evaluate the sub-threshold characteristics. The MOSFETs with boron ions implanted into the recess region showed a low drain current up to the gate bias of 10V. The result indicated that boron ion implantation prevented the formation of parasitic MOS-channel in the isolation region and achieved field isolation. The current-voltage characteristics of MOSFETs with the normal recess condition demonstrated no degradation of device performance after boron ions implanted into the isolation region. Boron ion implantation by further optimization can be a field isolation method for GaN MOSFETs.
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