GaN based HEMT sensor is a new type of sensor based on the surface state control of 2-D electron gas (2DEG) at AIGaN/GaN heterojunction. In GAN-based HEMT structures, a 2DEG surface channel is formed at the AIGaN/GaN interface of heterojunction. The 2DEG in the potential well is controlled by the gate voltage, and the 2DEG layer is very close to the surface and is very sensitive to the state of the surface. AIGaN/GaN heterobonds are highly sensitive to ions, polar liquids, hydrogen, and biological materials [1], and since then, researchers have started to study a series of sensors based on GAN-based HEMTs. At present, relatively mature research mainly includes gas sensors and biosensors [2].
Su et al. [3] developed a Pt NPs/AlGaN/GaN high electron mobility transistor (HEMT) device that demonstrated dual-gas detection of hydrogen (H2) and ammonia (ammonia) by adjusting the operating temperature only, suitable for applications such as multi-gas detection and electronic nose, as shown in the left figure of Figure 1. The GAN-based HEMT gas sensor, formed on a 20×20 mm Si (111) substrate by MOCVD, uses an AlGaN/GaN HEMT with an ordered layered structure including initial AlGaN/GaN/AlGaN. During the fabrication process, the ohmic contact Ti/Al/Ti/Au multilayer films were deposited by magnetron sputtering equipment. In order to form ohmic contact between the metal multilayer film and AlGaN, a rapid annealing for 60 s was performed in nitrogen using an infrared annealing furnace RTP (IRLA-1200, JouleYacht, China) at 650◦C. Figure 1 The right image shows the structure of a HEMT device, an optical image of the sensor array, a scanning electron microscope (SEM) image of a HEMT device, and an enlarged SEM image of a single device.