The Insertion of an AlN Spacer between the Barrier and the Channel Layer for a Polarization-Enhanced AlGaN-Based Solar-Blind Ultraviolet Detector

The AlGaN-based solar-blind ultraviolet (SBUV) detectors have tremendous potential applications in missile warning, secret communications, deep space exploration, etc. In this work, we have proposed a strategy to improve the response as well as the photo-to-dark current ratio (PDCR) of the AlGaN-based polarization-enhanced SBUV detector by inserting an AlN spacer between the high-Al barrier and the low-Al channel layer. On the one hand, the AlN spacer can enhance the polarization field and increase the effective conduction band offset, increasing the photogenerated electron–hole pairs' separation efficiency and channel conduction ability. On the other hand, the AlN spacer can lift the effective barrier height of the channel electrons, suppressing the dark current. Moreover, the AlN spacer can reduce the alloy disorder scattering and Coulomb scattering of the channel electrons, enhancing electron mobility. Consequently, an extremely low dark current below 1 pA and a PDCR exceeding 108 under an incident light power density of 5.4 μW/cm2 at 250 nm are obtained at 5 V. The spectral response shows a peak responsivity of 1.2 × 106 A/W, corresponding to a current gain of over 5 × 106, which is near 3 orders of magnitude higher than that of the reference detector without an AlN spacer layer. The light power density-dependent response and response time measurements are also performed to investigate the gain enhancement mechanism. The detectors are employed into a scanning imaging system to obtain a SBUV image to confirm the superiority of introducing an AlN spacer layer into AlGaN-based polarization-enhanced detectors in real applications.