Transmission characteristics of silicon-based grating-gated AlN/GaN HEMTs in the mid-infrared frequency range

Abstract

The grating-gated AlN/GaN HEMTs have demonstrated excellent light absorption capabilities across a wide mid-infrared frequency range, thus being suitable for subwavelength modulation device design. However, the impact of a substrate on the optical transmission characteristics of grating-gated AlN/GaN HEMTs was overlooked in previous studies, limiting the potential applications of the structure. To address the issue, the transmission characteristics of silicon-based grating-gated AlN/GaN HEMTs were researched in the paper. By employing an optical transmission matrix to derive the dispersion characteristics of silicon-based grating-gated AlN/GaN HEMTs, the phonon polaritons are excited in the GaN layer, particularly around 20 THz, significantly influencing the transmission characteristics of the structure. Simulations conducted in COMSOL indicate that employing silicon as a substrate for grating-gated AIN/GaN HEMTs can substantially diminish light absorption by around 20 THz. Decreasing gate length and GaN layer thickness can enhance transmissivity, while varying silicon substrate thickness minimally affects the transmissivity of grating-gated AlN/GaN HEMTs. Significant transmissivity oscillations near 20 THz suggest potential applications for designing mid-infrared filters around 17 THz. Subsequently, a predictive model for transmissivity of silicon-based grating-gated AlN/GaN HEMTs is established using CNN, with a significantly smaller MAE of 0.00809 and a larger R² of 0.98263 achieved. The predictive model accurately determines the required structure size of silicon-based grating-gated AlN/GaN HEMTs within a shorter time, reducing costs during design and manufacturing processes. The results underscore the significant future potential for utilizing silicon-based grating-gated AlN/GaN HEMTs in mid-infrared filters and other device designs.