High-Sensitivity Solar-Blind UV Phototransistor With Binary AlN/GaN Interface-Layer-Engineered AlGaN Heterojunction

Efficient detection of weak solar-blind ultraviolet signals demands high-concentration and high-mobility of two-dimensional electron gas (2DEG) in AlGaN-based heterojunction field-effect phototransistors (PTs). However, alloy scattering and interface defects in Al-rich AlGaN heterostructures degrade 2DEG properties, limiting photoresponse and stability. To address this, we introduce binary AlN/GaN interface layers at the Al<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.61</sub>GaN/Al<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.53</sub>GaN heterojunction, achieving a 25-fold increase in 2DEG sheet concentration (2.5×10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sup> cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup>) and a 36% mobility enhancement (268 cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>/Vꞏs). Simulations reveal that these enhancements originate from enhanced polarization charges and carrier confinement (increasing concentration) and reduced alloy scattering (improving mobility). The resulting PT exhibits a 3.5 times higher photocurrent and a peak detectivity of 3.6×10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">18</sup> Jones, significantly surpassing conventional designs. Furthermore, suppressed interface defects enable a three-order-of-magnitude faster response decay and a mitigated out-of-band response. This interface engineering strategy offers a practical solution for improving the 2DEG properties and device applications of Al-rich AlGaN heterojunctions.