Fig. 1. Schematic diagrams and locally enlarged optical microscope images of as-fabricated photodetector structures with (a) Gr-only, (b) lateral Gr-AlGaN, and (c) vertical Gr-AlGaN junctions. The cross-sectional device configuration of the corresponding photodetector is shown in the top-right. (d)–(f) Raman mapping for E2 band intensity of AlGaN (at the top) and 2D band intensity of graphene (at the bottom), in which the measured region is marked by red dashed line in (a)–(c).

Fig. 2. (a) Raman spectra of Gr-only, lateral Gr-AlGaN, and vertical Gr-AlGaN junctions for these designed photodetectors, which are extracted from their Raman mapping. (b) PL spectrum and (c) XRD rocking curve scanning of the AlGaN epilayer.

Fig. 3. (a)–(c) Logarithmic I–V curves of Gr-only, lateral Gr-AlGaN, and vertical Gr-AlGaN photodetectors working in dark (black line) and light (red line) conditions; the photocurrent is plotted as green lines. (d)–(f) I–V–T curves and (g)–(i) schematic diagrams of photocarrier transport behavior for these devices in (a)–(c).

Fig. 4. (a) Spectral response and (b) dependence of responsivity and detectivity on light power density for lateral Gr-AlGaN and vertical Gr-AlGaN photodetectors.

Fig. 5. (a) Schematic diagram of the imaging test and (b) distribution of light and dark states for the 3×3 photodetector array. (c) External circuit connection for the vertical Gr-AlGaN and lateral Gr-AlGaN photodetectors. (d) Real imaging by the vertical Gr-AlGaN photodetector array at zero bias and (e) dependence on the light illumination time by the lateral Gr-AlGaN photodetector array at the bias voltage of 2 V.

Fig. 6. (a) Optical microscope images of the entire lateral Gr-AlGaN and vertical Gr-AlGaN photodetectors. (b) Schematic plan-view of paired metal electrodes.

Fig. 7. Energy band diagram of the Gr-AlGaN junction under the light illumination.

Fig. 8. (a) Power density-dependent I–V–T curves of lateral Gr-AlGaN and (b) vertical Gr-AlGaN photodetectors, working at a bias voltage of 2 V and 0 V, respectively.

Fig. 9. I–V–T curves of the lateral Gr-AlGaN photodetector (at zero bias) and vertical Gr-AlGaN photodetector (at 2 V).

Table 1. Comparison of Photodetector Performance for Those Based on Gr-(Al)GaN Junctions