Si-based metal-semiconductor-metal photodetectors with various design modifications

We have designed and fabricated interdigitated metal-semiconductor-metal photodetectors (MSM-PD's) on n-type amorphous Si/crystalline Si (a-Si:H/c-Si). Both thick and thin silicon dioxide (SiO₂) layers were grown to reduce dark current and passivate the surface. Au, Cr, Ni, and Pd metals were used for metallization. The dark current for the detector (0.75 × 0.5 cm²) with the added a-Si film was reduced from 0.137 mA to 2.61 μA at 5 V when compared with that of the conventional Si-based film. Its magnitude was found to be at least two orders lower than that of the conventional sample. Simple metal/Si Schottky diodes were fabricated with substrates at RT and low temperature (LT). It was found that Schottky barrier height was improved with cryogenic metallization processing. Both dark current and speed were significantly improved as metallization temperature decreased. The full width at half maximum (FWHM), rise time, and fall time at 800 nm reduced from 0.47 μs to 6.2 ns, 49.7 ns to 23.9 ns, and 2.07 μs to 0.41 μs, respectively, as substrate temperature during metallization decreased from room temperature (RT) to 210 K. Schottky barrier height and ideality factor for the LT samples were increased from 0.399 eV to 0.481 eV, and 3.76 to 4.64, respectively, compared to that of the RT sample at 150 K. The current-voltage-temperature (I-V-T) analysis showed that thermionic field emission dominated the current transport in the forward current region.