N+/P and P+/N Junctions in Strained Si on Strain Relaxed SiGe Buffers: the Effect of Defect Density and Layer Structure

Abstract

The electrical performance of junctions in SiGe Strain Relaxed Buffers (SRB’s) with a strained Si top layer is investigated. Most of the SRB’s grown in this experiment use a thin C-doped SiGe layer, which allows to fabricate thin (∼250nm) SRB’s with a high relaxation degree. The effects of Threading Dislocation Density (TDD) and C-rich layer depth on the electrical behaviour of n+/p and p+/n junctions are studied. The C atoms in the junction’s Space Charge Region (SCR) give rise to defects and induce a noticeable increase in the leakage. The effect of the TDD on the leakage in n+/p junctions is linear over the complete voltage range applied, while for p+/n junctions, only a small effect on leakage is measured at V=1V reverse for TDD’s below 1×10⁷cm^-2. For low reverse voltages, the current varies more linearly with TDD.