Fig. 1. (a)–(e) Si MSM photodiode with photon-trapping holes. (a) Schematic of the high-speed photodiode integrated with holes. (b) Section of the photodiode structure on an SOI wafer. (c) Holes in the square lattice. (d) Holes in the hexagonal lattice. (e) SEM image of the active region of a Si MSM photodiode (50 µm diameter). (f) Schematic and (g) SEM image of a PbSe-on-Si MSM photodiode (50 µm diameter).

Fig. 2. FDTD simulated absorption and photon distribution in the Si and PbSe-on-Si films with photon-trapping holes. (a), (b) Absorption of Si films on the SiO₂ substrates with different designs of hole arrays between 800 and 950 nm. (a) Absorption of Si films with holes of different diameters, periods, and arrangements. (b) Absorption of Si films with holes of different depths. (c), (d) Absorption of the PbSe films on the SOI substrates with hole arrays between 800 and 1600 nm. (c) Absorption of the PbSe films with holes of different diameters, periods, and arrangements. (d) Absorption of the PbSe films with holes of different depths. (e) Photon distribution in the Si photodiodes without holes (top), with holes in the hexagonal lattice with d/p of 630/900 nm (middle), and with holes in the hexagonal lattice with d/p of 1500/2000 nm (bottom) under vertical incidence at 850 nm. The color bar on the right shows the color map of the photon distribution probability density. (f), (g) Electric field distribution in the nanostructured PbSe films on the SOI substrates with d/p of 700/1000 nm (f) and 1400/2000 nm (g) at the wavelength of 980 nm. The holes are arranged in a square lattice with a depth of 150 nm.

Fig. 3. (a)–(d) Calculation of light deflection, back reflection, and top transmission in the Si films with different periods of holes. (a) Transmission efficiency (T_N) from the hole array to the flat Si layer, and deflection angles (θ_N) of different orders for the hole arrays with d/p of 630/900 nm and 1500/2000 nm at the wavelength of 850 nm. (b) Reflectivity (r_N) at the Si/SiO₂ interface for the transmitted light with different orders from the hole arrays with d/p of 630/900 nm and 1500/2000 nm at 850 nm wavelength. (c) Transmission in the flat Si layer and the back reflection of the SiO₂ substrate for the hole arrays with d/p of 630/900 nm and 1500/2000 nm at 800 nm, 830 nm, 850 nm, 870 nm, and 900 nm. (d) Top transmission (T_N^′) of the bottom incident light with different incident angles for the hole arrays with d/p of 630/900 nm and 1500/2000 nm. Inset: schematic of the light reflected by the SiO₂ film and then transmitted from the hole array into the air from the top Si surface (T_N^′). (e), (f) Electric field distribution over time in the nanostructured Si films with d/p of 700/1000 nm (e) and 1500/2000 nm (f) at the wavelength of 850 nm.

Fig. 4. Enhanced EQE and ultra-fast response of the Si MSM photodiodes. (a) I-V curves of the photodiodes with holes in the hexagonal lattice with d/p of 690/900 nm under 850 nm illumination and in dark conditions. (b) The photocurrent of the photodiode with holes in the hexagonal structure with d/p of 630/900 nm at different light power intensity. (c) Measured EQE of the photodiodes with different hole structures at 850 nm. (d) Measured impulse response at −3 V, −5 V, and −8 V bias from the photodiode with holes in the hexagonal lattice with d/p of 630/900 nm. (e) Gaussian fitting curve of the impulse response of the photodiode with holes in the hexagonal structure with d/p of 630/900 nm at −5 V bias. (f) Calculated 3 dB bandwidth of the photodiode with holes in the hexagonal structure with d/p of 630/900 nm.

Fig. 5. Characterization and performance of the PbSe MSM photodiodes with hole arrays. (a) Raman spectrum of PbSe film. Inset: AFM image of the film. (b) I-V curves of the devices with different hole structures in dark conditions. (c) I-T curves of the devices with different hole structures at 2 V bias. (d), (e) EQE (d) and EQE enhancement (e) of the devices with different hole structures at 808–1550 nm. (f) Noise characteristic of the devices with different hole structures at −2 V bias.