Dark Current Reduction of Avalanche Photodiode Using Optimized InGaAsP/InAlAs Superlattice Structure

We studied reduction in dark current of avalanche photodiodes (APDs) using an optimized InGaAsP/InAlAs superlattice (SL) structure, which was fabricated by gas-source molecular beam epitaxy. For the sample which has the thickest barrier and the thinnest well, the dark current value of 0.4 µA at a multiplication factor of 10 was achieved. This is the lowest dark current for InGaAsP/InAlAs SL-APDs to our knowledge. This result shows that the band-to-band tunneling current, which affects dark current, was suppressed by increasing the effective band gap energy of the SL multiplication layer. Moreover, we discussed the mechanism of avalanche multiplication and confirmed the reason why sufficient avalanche multiplication occurred in optimized InGaAsP/InAlAs SL-APD even at low electric field. It was concluded that an optimized InGaAsP/InAlAs SL structure effectively enhances electron impact ionization and also improves dark current.