On the alloying and strain effects of divacancy energy level in n-type Si1 − xGex

Abstract

Deep level transient spectroscopy was used to investigate point defects introduced by room temperature He-ion irradiation in both fully strained and partially relaxed phosphorous doped n-type Si1 − xGex films epitaxially grown on the Si (001) substrate by chemical vapor deposition. Two major point defects are identified as the doubly negative charge state of the divacancy (V2=/−) and the V-P pair (E-center). The activation enthalpy (EH) of V2=/− was investigated upon strain and alloying effects in order to quantify their individual impact. The deduced variation of activation enthalpy associated with the sole strain effect in strained films is found to decrease linearly as a function of strain (tetragonal mismatch), corresponding to 56 meV/GPa regardless of the degree of strain relaxation for 0 ≤ × ≤ 0.1. This result may suggest that while the strain and alloying have an additive effect on the variation of EH, may however have different physical origins.