Type-II photodiode and APD for detection in the 2–2.5 µm wavelength range

The authors report the avalanche characteristics of the type-II absorption region when subjected to electric fields ranging from 60 kV/cm to 260 kV/cm and compare its behaviour to that of bulk In_0.53Ga_0.47As. Electron and hole initiated multiplication is performed on the type-II PIN photodiodes with 150 pairs of In_0.53Ga_0.47As/GaAs_0.51Sb_0.49 layers in the intrinsic region and highly doped In_0.53Ga_0.47As claddings. The electron to hole ionization ratio is found to be large, and the ionization behaviour of this type-II material system is found to be fairly similar to that of In_0.53Ga_0.47As. SACM avalanche photodiodes (APDs) utilising the type-II absorption layer is also reported with InAlAs as the multiplication layer with a cut off wavelength of 2.5 mum. The device exhibited low dark current densities at punchthrough of 5.5 mAcm^-2 at room temperature and nearly 3 orders of magnitude lower dark currents at 200 K. The breakdown voltage temperature dependence is 40 m V/K, which is lower compared to that of a SACM APD with InP as the multiplication layer. The device also exhibited gains >100 at 200 K.