Fig. 1. Schematic diagram of Al0.5Ga0.5N/AlN solar-blind UV photodetector, including (a) plan-view of interdigitated electrodes and (b) cross-sectional view, illustrates the separation of electron–hole pair generated by incident UV signal under the action of polarization electric field in the self-depleted Al0.5Ga0.5N layer.

Fig. 2. (a) (0002) plane and (101¯5) plane ω-scan curves of the epitaxial sample with the 70-nm-thick n-Al0.5Ga0.5N layer. (b) Transmission spectrum of the epitaxial sample. The inset shows the spectrum. Surface potential maps of (c) 70-nm and (d) 100-nm n-Al0.5Ga0.5N channel layers measured on 5  μm×5  μm area by KFAM using Pt-Ir tip. The map consists of 256×256 pixels, and thus each pixel represents a square with a side length about 20 nm.

Fig. 3. Dark and illuminated I–V curves of the n-Al0.5Ga0.5N/AlN photodetectors with (a) 70-nm channel layer and (b) 100-nm channel layer. (c) Gain characteristics and (d) noise power spectral density of the corresponding two device samples.

Fig. 4. Photoresponse characteristics of the FCSD phototransistor. (a) Spectral responses at different bias voltages. (b) Bias dependence of responsivity at 240 and 280 nm. (c) Time and irradiation intensity dependence of the response current under 5-V bias, in which the irradiation uses periodic DUV illumination with periodic on/off times of 10/20 s. (d) Transient responses to the 213-nm pulse signal with an optical power density of 127.3  mW/cm2 at 20-V bias. The inset shows an enlarged view of a single impulse response.

Fig. 5. (a) I–V curves of the FCSD phototransistor under different incident DUV intensities. I–V curves in the bias range of 0–2 V under irradiation intensities of (b) 5.2  μW/cm2 and (c) 0.7  nW/cm2. (d) Photocurrent, (e) responsivity, and (f) detectivity as a function of irradiation power density (0.2  nW/cm2−138.3  μW/cm2) under different applied voltages, in which the solid lines are the theoretical results. (g) Extracted gain and PDCR at 20-V bias as a function of irradiation power density.

Fig. 6. (a) Schematic diagram of the neutral conductive path formed in the n-AlGaN channel of FCSD phototransistor under DUV irradiation due to the action of virtual photogate (separation of photogenerated electrons and holes). (b) Schematic diagram of energy band under dark and on illumination conditions.