Abstract
The electron and hole avalanche multiplication characteristics have been measured in bulk AlAs0.56Sb0.44 p-i-n and n-i-p homojunction diodes, lattice matched to InP, with nominal avalanche region thicknesses of ~0.6 μm, 1.0 μm and 1.5 μm. From these and data from two much thinner devices, the bulk electron and hole impact ionization coefficients (α and β respectively), have been determined over an electric-field range from 220–1250 kV/cm for α and from 360–1250 kV/cm for β for the first time. The α/β ratio is found to vary from 1000 to 2 over this field range, making it the first report of a wide band-gap III-V semiconductor with ionization coefficient ratios similar to or larger than that observed in silicon.
Highlights
Semiconductor based avalanche photodiodes (APDs) are widely used in long haul optical communication systems to increase the sensitivity of high speed receivers
AlAs0.56Sb0.44 has a relatively large indirect band-gap of ~1.65 eV and is lattice matched to InP
We report for the first time the α and β in AlAsSb covering a wide range of electric fields
Summary
Semiconductor based avalanche photodiodes (APDs) are widely used in long haul optical communication systems to increase the sensitivity of high speed receivers. When subject to a large electric-field, the electrons and holes can gain sufficient energy to undergo impact ionization, increasing the number of carriers and thereby providing internal gain This large electric field can cause high tunnelling dark currents in narrow band-gap semiconductors and the stochastic nature of the impact ionization process can give rise to a high associated ‘excess’ noise which mitigates the effect of the gain. Recent publications have suggested that the AlInAsSb12,13 alloy may have a large α/β ratio (~50–100), based on the evidence of very low excess noise measurements in thick avalanching structures This alloy has a relatively large band-gap (at the higher aluminium mole fractions) with low dark currents at room temperature but it needs to be grown on more expensive GaSb substrates. These α and β are capable of fitting the multiplication characteristics in our devices with ~660 nm-1550 nm thick p-i-n and n-i-p structures and structures with avalanching widths as thin as 230 nm[14]
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