Superlattice avalanche photodiode with a gain-bandwidth product larger than 100 GHz for very-high-speed systems

Even for lightwave transmission systems above 10 Gbit/s, highly sensitive and compact photoreceivers are preferable. An avalanche photodiode (APD) with a large gain-bandwidth (GB) product would be one of the most promising candidates for receivers in systems with such extremely high bit rates, as well as in systems with lower bit rates.1 Recently, we reported a superlattice (SL) APD with a GB product of 80 GHz under a 3-dB bandwidth of 12 GHz,2 where the SL allowed us to enhance the ionization-rate ratio for achieving the high GB product.3 To improve the GB product further, it is necessary to reduce the SL multiplication-layer thickness4 by overcoming the problem of the accompanying tunneling breakdown with thinning of the SL layer thickness. Here, we demonstrate an InAlAs/InGaAs SL-APD with a GB product of 130 GHz under a 3-dB bandwidth of 12 GHz by introducing a novel SL structure of less than 0.2-µm thickness.