Substrate-Dependent Cryogenic and UV Performance of AlGaN/AlN/GaN HEMTs and Photodetectors

Abstract AlGaN/AlN/GaN high-electron-mobility transistors (HEMTs) and metal–semiconductor–metal photodetectors (MSM-PDs) were integrated on Al2O3 and 4H-SiC substrates to quantify the impact of substrate selection on cryogenic electrical stability and ultraviolet (UV) optoelectronic performance. The HEMT/SiC structure exhibited a higher peak transconductance (gm) of 1.56 mS/2.34 mS at 300 K/130 K compared to the HEMT/Al2O3 structure (1.27 mS/1.83 mS). At 300 K, the gate-source voltage corresponding to peak gm was −0.3 V for the HEMT/SiC compared to −2.1 V for the HEMT/Al2O3, indicating different strain-induced polarization effects. For integrated sensing, the peak relative spectral response wavelengths were observed at 300 nm (on Al2O3) and 370 nm (on SiC). High-resolution characterization confirms that improved crystal quality and carrier transport in SiC-based heterostructures result from reduced lattice mismatch at the GaN/SiC interface. These findings establish the AlGaN/AlN/GaN-on-SiC platform as a compelling architecture for high-efficiency, switching GaN electronics and integrated cryogenic optoelectronic applications.