Unveiling the abnormal response behavior of AlGaN-based high electron mobility transistors (HEMTs) under ultraviolet light illumination

This study examines the dual functionality of AlGaN/GaN HEMTs as both power transistors and UV photodetectors, motivated by manipulating the bias dependent photoresponse and to perform both functions using AlGaN/GaN HEMT configuration seamlessly. The fabricated HEMTs achieve good electrical performance, with a maximum drain current I_DS of 547 mA/mm and an ON-to-OFF current ratio (I_ON/I_OFF) of 1.2 × 10⁷, with a threshold voltage of −3.9 V. The device demonstrated a peak responsivity of 758.4 A/W at 360 nm with an optical gain of 2617 under forward bias. When biased between −4.6 V < V_GS < V_th and V_DS = +3 V, UV illumination significantly increases the 2DEG channel conductivity, resulting in enhanced electron transport and high responsivity. However, as V_GS increases, dark current rises, limiting the gain improvement. Additionally, the proposed AlGaN HEMTs showed a UV sensing performance with a linear dynamic range (LDR) of 65.4 dB, indicating potential for UV detection applications. Furthermore, these devices can also operate in reverse conduction (third quadrant), achieving 220.7 A/W when V_DS < 0 V and V_GS + V_SD > V_th. Applying a higher drain-source voltage further boosts responsivity by strengthening the lateral electric field, but only if dark current remains low. Finally, the HEMTs detect optical pulses at 550 Hz with response times of 641 μs and 776 μs (τ_r/τ_f). These capabilities allow the device to function as both a power signal driver and an optical detector without structural modifications, making it a versatile option for multifunctional applications.