Proton irradiation effects on strained Si1−xGex/Si heterostructures

Abstract

Proton irradiation effects on strained Si1−xGex/Si heterostructures have been studied. For the experiment, p+-Si1−xGex/p−-Si heterojunction diodes were fabricated by molecular beam epitaxy (MBE) growth of strained p+-boron doped SiGe layers on p−-Si(100) substrates. Due to the valence band discontinuity between SiGe and Si layers, and degenerate doping in the SiGe layer, the characteristics of these heterojunction diodes are similar to those of metal-semiconductor Schottky barrier diodes. The SiGe/Si heterojunction diodes are irradiated by 1 Mrad of protons at 1 and 8.5 MeV energies. The current-voltage (I-V) characteristics are measured as a function of temperature before and after irradiation. I-V characteristics show a decrease of the reverse bias leakage current after irradiation. The effective heterojunction barrier heights (Φb) and Richardson constants (A**) are measured before and after irradiation using activation energy measurements. The measurements show an increase of Φb and A** after irradiation. The increase of the effective barrier height is attributed to reduction of free-holes in the SiGe layers due to proton induced displacement defects. The increase of effective barrier height suggests that the strain in the SiGe layers is conserved after 1 Mrad of proton irradiation.