Room-temperature terahertz emission from N-polar GaN grating-gate high-electron-mobility transistors

Abstract

Compact, electrically driven terahertz (THz) sources remain a major bottleneck for chip-scale spectroscopy, imaging and high-speed wireless links. AlGaN/GaN two-dimensional electron gas (2DEG) systems have been investigated for THz emission, but experimental demonstrations have almost exclusively used Ga-polar platforms. Here we report a room-temperature THz signal from N-polar GaN grating-gate high-electron-mobility transistors (HEMTs) under pulsed electrical excitation. In the reversed-polarization heterostructure, the GaN channel lies above the AlGaN barrier, a geometry that places the channel close to the surface grating. The detected THz power increases with lateral electric field and square-wave duty cycle, whereas the apparent conversion efficiency falls at high duty cycle, consistent with increased Joule heating. Spectral measurements reveal a broad low-frequency feature and a gated/ungated spectral difference. The long-pulse room-temperature response is consistent with predominantly thermal emission, and the gated/ungated difference may reflect geometry-dependent thermal emissivity. These measurements do not establish a separate collective 2DEG contribution or a plasmonic resonance. These results establish an experimental N-polar GaN HEMT platform for studying electrically driven THz radiation and motivate calibrated emissivity, polarization-resolved and gate-tunable measurements.