Trap-assisted tunneling in the reverse dark current of GaAlAsSb avalanche photodiodes

Numerous applications in the 1.0 to 1.6 µm spectral range require avalanche photodetectors that have both a large gain-bandwidth product and high sensitivity (1). Recent reports indicate a large asymmetry in the impact ionization ratio ( ) for Ga1-xAlxSb (x ∼ 0.065) (2) material. The resultant increase in the gain-bandwidth product makes the study of this alloy system important. With the low excess noise factor available in this material, if low dark currents can be achieved, the result will be extremely high performance avalanche photodiodes. Unfortunately, GaA1Sb devices have hitherto been plagued by surface leakage currents. Through significant design and processing changes, however, we have fabricated GaAlAsSb devices which are free of large surface leakage currents. This has allowed a detailed study of the bulk reverse current characteristic of these devices. The reverse dark current of Ga0.8Al0.2ASySb1-yavalanche photodiode was measured over a wide temperature range. At low temperatures, the current is dominated by a tunneling component which has been identified as defect tunneling because the tunneling energy is considerably less than the bandgap energy. Identification of the tunneling process responsible for this current as defect tunneling is supported by a second tunneling component which becomes dominate at high electric fields.