Infrared spectra of hydrogen bound to group-III acceptors in Si: Homogeneous line broadening and sidebands

Abstract

We report spectral features of localized vibration of hydrogen bound to group-III acceptors in Si. To avoid the Fano effect on the line broadening, we homogeneously doped specimens with group-III acceptors and hydrogen with low concentrations; consequently, the line shapes were well fitted by Lorentzian functions, indicating that the shapes were affected by two dynamical effects, i.e., energy relaxation and dephasing. While the spectra of B-H, Al-H and Ga-H pairs were found to show only one sideband in the lower-frequency region of the main peak, sidebands appeared in both the lower-and higher-frequency regions in the case of In-H. This appearance of the sidebands in the case of In-H pairs was unexpected from a previous model [M. Stavola et al., Phys. Rev. B 37, 8313 (1988)]. By analyzing the linewidth of the main peak at around 6 K, we estimated the energy relaxation times T 1 , which were found to be much shorter than those previously observed for the complexes of the point defect and H in Si. Moreover, we also found a chemical trend: As the covalent radius of the group-III acceptor increased, the T 1 became shorter. Temperature dependences of the linewidth and peak shift of the main peak were analyzed based on dephasing models. The analysis showed that the experimental results cannot be explained by the Persson-Ryberg model in the weak-coupling limit of the anharmonic coupling between the local vibrational mode and hath ones, suggesting that the anharmonic coupling is intermediate or strong.