Demonstration of Flame Detection in Room Light Background by Solar-Blind AlGaN PIN Photodiode

We have fabricated n-Al0.44Ga0.56N/i-Al0.44Ga0.56N/p-GaN heterojunction photodiodes with a cut-off wavelength of 275 nm. The multilayer device structure was grown by metal-organic vapor phase epitaxy using a low-temperature interlayer technique. Thanks to the high quality AlGaN, the responsivity dropped steeply by three, five and six orders of magnitude at the AlGaN bandedge of 275 nm, 600 nm, and 1 μm, respectively. The steep bandedge enables a minimum leakage of effective weak-flame luminescence between 250 and 280 nm. For flame detection, a visible cut-off filter to assist the selectivity to the flame luminescence was attached. In addition, the photodiode was operated at zero-bias so that the darkcurrent does not exceed the weak photocurrent induced by flame luminescence. This solar-blind photosensor thus successfully responded selectively to the flame luminescence regardless of whether the room was lighted or not.