Effects of the intrinsic layer width on the band-to-band tunneling current in p-i-n GaN-based avalanche photodiodes
Dark current is critical for GaN-based avalanche photodiodes because it significantly increases the noise current and limits the multiplication factor. It has been found that the band-to-band tunneling current is the dominant origin of the dark current for avalanche photodiodes at the onset of breakdown voltage. Experimentally, for GaN-based avalanche photodiodes with a thinner intrinsic layer, the dark current increases nearly exponentially with the applied voltage even at a lower bias voltage. In this paper, the intrinsic layer (i-layer) width of GaN-based avalanche photodiodes has been varied to study its effect on the band-to-band tunneling current. A widely used equation was used to calculate the band-to-band tunneling current of avalanche photodiodes with different i-layer widths (i-layer 0.1 μm, 0.2 μm and 0.4 μm). At −40 V, the band-to-band tunneling current significantly reduces by a magnitude of 10 −15 A with an increase in the i-layer width from 0.1 μ mt o 0.2μm, and a magnitude of 10 −29 A with an increase in the i-layer width from 0.2 μ mt o 0.4μm. Then, GaN-based avalanche photodiodes (i-layer 0.1 μm, 0.2 μm and 0.4 μm) with different-sized mesa were fabricated. Also, the measurement of dark current of all three different structures was performed, and their multiplication factors were given.