Impact ionisation in GaAs planar-doped barrier structures grown by molecular layer epitaxy

The I-V characteristics and substrate current of GaAs planar-doped barrier (PDB) n+-i-p+-i-n+ structures with various barrier heights (0.5-0.8V) grown by molecular layer epitaxy (MLE) have been measured at temperatures ranging from 77 to 296K. The measurement was carried out at the constant source-drain distance of 1000A. It is found that an abrupt increase in the drain current occurs, in the high barrier (>0.73V) PDB structures at a threshold bias voltage FTH. The value of FTH decreases from 3.1 to 2.7V with increasing temperature from 77 to 296K, and the coefficient is -1.8 mV/K. The ratio of KTH and GaAs bandgap Eg is obtained to be eV-4E-4 = 2. The mechanism of the abrupt increase in the drain current is attributed to the effects of ballistic electron transport and the lowering of the potential barrier by the accumulation of impact-ionisationgenerated holes at the p+ plane. Furthermore, this mechanism is confirmed by the results of photocurrent measurements, in which holes are generated by incident light. The obtained results have important implications for the design of the barrier height in PDB structures and other devices having thin potential barriers.