A novel ion-imprinted electrochemical sensor based on AlGaN/GaN high electron mobility transistors (HEMTs) was developed to detect trace amounts of phosphate anion. This sensor combined the advantages of the ion sensitivity of AlGaN/GaN HEMTs and specific recognition of ion imprinted polymers. The current response showed that the fabricated sensor is highly sensitive and selective to phosphate anions. The current change exhibited approximate linear dependence for phosphate concentration from 0.02 mg L−1 to 2 mg L−1, the sensitivity and detection limit of the sensor is 3.191 μA/mg L−1 and 1.97 μg L−1, respectively. The results indicated that this AlGaN/GaN HEMT-based electrochemical sensor has the potential applications on phosphate anion detection.

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AlGaN/GaN high electron mobility transistors (HEMTs) have demonstrated their extraordinary potential in developing solid-state microsensors for detecting gases, metal ions, anions, biomolecules, and other substances due to their excellent chemical stability, high surface charge sensitivity, high temperature-tolerance performance, and low power consumption characteristics. In this paper, only three types of AlGaN/GaN HEMT-based sensors used for detecting the pH value, heavy metal ions, and harmful anions, which are suitable for water quality monitoring, will be discussed. First, we introduce the structural design, detection principle, and fabrication processes of AlGaN/GaN HEMT-based sensors. Then, surface functionalization methods for the gate region, sensing mechanisms, and the sensitivity and selectivity performances based on different gate region treatments are reviewed and analyzed. Finally, some challenging problems that hinder the practical application of the sensors are proposed.

In this paper, a first study on phosphate detection based on AlInN/ GaN high electron mobility transistors (HEMTs) is presented. The ungated regions of GaN HEMT-based sensors were functionalized with the phosphate ion-imp rinted poly mer and their sensing behaviors were analyzed by detecting different concentrations of phosphate solutions. The results show that the AlInN/ GaN sensor exhibits an ultrasensitive response and a specific recognition to phosphate anion and reaches a detection limit belo w 0.02 mg/ L level, wh ich is much lower than the limited indicator level of 0.1 mg/ L for the plankton growth. Meanwh ile, the A lInN/ GaN sensor shows a higher sensitivity to phosphate anion when compared with the AlGaN/ GaN sensor. This ultra-h igh sensitivity is attributed to the use of thinner barrier layer in the AlInN/ GaN heterostructure, which makes two-dimensional electron gas channel more sensitive to the change of surface charge. Index Terms-AlInN/GaN, ion-imprinted polymer, phosphate anion detection, thinner barrier