Vibrational lifetimes of hydrogen in silicon

Abstract

Characterization of defect and impurity reactions, dissociation, and migration in semiconductors requires a detailed understanding of the rates and pathways of vibrational energy flow, of the energy transfer channels, and of the coupling mechanisms between local modes and the phonon bath of the host material. Significant progress in reaching this goal has been accomplished in recent landmark studies exploring the excitation and dynamics of vibrational states associated with hydrogen in silicon. The lifetime of the Si-H stretch mode is found to be extremely dependent on the local solid-state structure, ranging from picoseconds for interstitial-like hydrogen, hundreds of picoseconds for hydrogen-vacancy complexes, to several nanoseconds for hydrogen bonded to Si surfaces-over three orders of magnitude variation. Such large variations in lifetime ͑transition probability͒ are extraordinarily rare in solid-state science. The level of theoretical investigation into the vibrational lifetime of the Si-H oscillator is less advanced. This state of affairs is partly because of the difficulties in explicitly treating slow relaxation processes in complex systems, and partly because, as suggested by experiment, a highly anharmonic coupling mechanism is apparently responsible for the ͑multiphonon͒ relaxation process. Even more importantly, because of the high frequency of the Si-H stretching motion, a quantum mechanical treatment of the Si-H oscillator is required. A combination of Bloch-Redfield theory and molecular dynamics simulation seems promising in describing the relaxation process of the Si-H vibrational modes. It is the aim of this review article to present a comprehensive overview of the recent accomplishments, current understandings, and future directions in this emerging field of time-resolved vibrational spectroscopy of point defects in solids.

Huge isotope effect on the vibrational lifetimes of an H2*(C) defect in Si

“…The added potential energy in this Si 64 cell results in the net temperature to increase to ∼ 120 K. Since the IR line widths are measured at low T, the calculated τ 's are expected to be somewhat shorter than the low-T ones (measured τ (T) are in Refs. [17,18,[29][30][31]). …”

“…Direct measurements of vibrational lifetimes [17] involve transient bleaching spectroscopy and access to a fast-pulse laser. However, τ can also be estimated from the IR line width.…”

Thermal conductivity of Si nanostructures containing defects: Methodology, isotope effects, and phonon trapping

“…Such effects can be dramatic when substituting D for H, 11 but one could argue that the mass changes by a factor of 2. However, the lifetime of the asymmetric stretch of interstitial O in Si is highly sensitive to the isotope of one of its Si neighbors.…”

“…Experimental [10][11][12] and theoretical [12][13][14] studies have shown that the lifetimes of highly localized vibrational modes of light impurities in Si can vary by up to two orders of magnitude. In some cases, a simple isotope substitution has a surprisingly large impact on the lifetime of a specific mode, as a fast two-phonon decay becomes a much slower three-or even four-phonon decay.…”

Reconfiguration and dissociation of bonded hydrogen in silicon by energetic ions

“…However, the multiple vibrational excitation mechanism is temperature dependent as the vibrational lifetime of the local modes of Si-H complexes decreases with increase in temperature [21][22][23], reducing the efficiency of this "vibrational state-ladder climbing" process. Hence our temperature dependence data suggests that secondary electron induced multiple vibrational excitation may be responsible for the observed site changes and dissociation of defect associated…”