PROTON IRRADIATION EFFECTS ON STRAINED SI1-XGEX SI HETEROSTRUCTURES/

Proton irradiation effects on strained Si1-xGex/Si heterostructures ha ve been studied. For the experiment, p+-Si1-xGex/p--Si heterojunction diodes were fabricated by molecular beam epitaxy (MBE) growth of strai ned p+-boron doped SiGe layers on p--Si(100) substrates. Due to the va lence band discontinuity between SiGe and Si layers. and degenerate do ping in the SiGe layer, the characteristics of these heterojunction di odes are similar to those of metal-semiconductor Schottky barrier diod es. The SiGe/Si heterojunction diodes are irradiated by 1 Mrad of prot ons at 1 and 8.5 MeV energies. The current-voltage (I-V) characteristi cs are measured as a function of temperature before and after irradiat ion. I-V characteristics show a decrease of the reverse bias leakage c urrent after irradiation. The effective heterojunction barrier heights (PHI(b)) and Richardson constants (A*) are measured before and after irradiation using activation energy measurements. The measurements sh ow an increase Of PHI(b) and A* after irradiation. The increase of th e effective barrier height is attributed to reduction of free-holes in the SiGe layers due to proton induced displacement defects. The incre ase of effective barrier height suggests that the strain in the SiGe l ayers is conserved after 1 Mrad of proton irradiation.