T-shaped gate AlGaN/GaN HEMTs fabricated by femtosecond laser lithography without ablation

Abstract

Femtosecond laser as a maskless lithography technique is able to fabricate structures far smaller than the diffraction limit to a value within sub-micrometer resolution. We present the femtosecond laser lithography without ablation on the positive photoresist is applied in fabricating T-shaped gate AlGaN/GaN HEMT. The feature sizes of femtosecond laser lithography were determined by the incident laser power, the scan speed of the laser focus, the number of scan times, and the substrate materials. T-shaped gate with the smallest gate length 204 nm could be fabricated by dielectric-defined process using femtosecond laser lithography. The fabricated AlGaN/GaN HEMT with 380 nm T-gate exhibits a maximum drain current density of 500 mA/mm and a maximum peak extrinsic transconductance of 173 mS/mm.