Pressure dependence of the configurational bistability and deep electronic levels of the MFe center in InP

Abstract

The influence of hydrostatic pressure on the structural bistability and electronic properties of the processing-induced MFe center in Fe-doped $n$-type InP was investigated. Earlier work has shown that, when occupied by electrons, the center can be reversibly placed in either of two configurations, termed $A$ and $B$, by the proper choice of electric biasing conditions and temperature. Pressure strongly modifies the energetics and kinetics of the various electronic transitions and of the transformations associated with the center. The activation volumes $(\ensuremath{\Delta}{V}^{*})$ for these processes were determined. In the absence of barriers to electron capture, or for small barriers, $\ensuremath{\Delta}{V}^{*}$ can be interpreted as the breathing mode relaxation associated with electron emission or capture. At pressures $\ensuremath{\geqslant}8\phantom{\rule{0.3em}{0ex}}\mathrm{kbar}$, the center exists only in the $A$ configuration regardless of bias conditions, because at these pressures the energetics and kinetics of the various processes have changed so much as to always favor the $A$ configuration. It is also shown that, whereas the $A\ensuremath{\rightleftarrows}B$ transformations are charge state controlled at $1\phantom{\rule{0.3em}{0ex}}\text{bar}$, this is not the case at high pressure where the transformations can be brought about without electron emission or hole capture. Earlier tentative atomic models for the center are discussed, and it is shown that some features of one of the models including the signs of the breathing mode relaxations associated with the various electron emissions are consistent with the experimental results, but issues remain. The results are also found to be generally consistent with first-principles calculations on defects in InP, but it is emphasized that whereas these calculations are for simple defects, the defects associated with the MFe center are more complex.