The superlattice photodetector: A new avalanche photodiode with a large ionization rates ratio

The first superlattice avalanche photodiode (APD) is reported. The high field region of this p-i-n structure consists of 50 alternating Al0.45Ga0.55As 550Å) and GaAs (450Å) layers. We find an ionization rates ratio α/β=8 at a gain of 10. The ionization rate ratio enhancement with respect to bulk GaAs and AlGaAs is attributed to the large difference in the band edge discontinuities for electrons and holes at the heterojunction interfaces. The superlattice APD is a new device concept which can also be used to develop low noise APD´s in long wavelength 1.3-1.6µm semiconductors.