Vibrational lifetimes and isotope effects of interstitial oxygen in silicon and germanium

The spectral bandshape of the ν(3) (1136 cm(-1)) vibration of oxygen in silicon and dilute silicon-germanium alloys

At room temperature, the ν(3) (1136 cm(-1)) absorption band of oxygen in silicon and Si(1 - x)Ge(x) alloys consists of dozens of components, masking the properties of the individual transitions. Here, experimental data are presented for the evolution of the ν(3) band in the temperature range 0 < T < 300 K and the composition range 0 ≤ x ≤ 0.066. The vibrational potential for Si:O is developed to provide accurate fits to the absorption data. The potential predicts properties consistent with published studies, including hydrostatic stress experiments. Extending the model to Si(1 - x)Ge(x) allows the properties of the alloy-induced O(i)-I, O(i)-II and O(i)-III components to be investigated accurately to higher values of x than hitherto. The properties of O(i)-I are understood as perturbations by Ge atoms of Si:O, and O(i)-III is rationalized in terms of off-axis movement of the O atom resulting from the nearby Ge atom. Challenges to theory are: the behaviour of O(i)-II, understanding the strain fields generated by Ge atoms in Si, and the reduced coupling of the ν(2) and ν(3) modes with increasing amplitude in the ν(2) mode.

Control of impurity diffusion in silicon by IR laser excitation

Control of the diffusion of a specific impurity species is desirable in Si device processes. IR laser excitation matching the impurity vibration mode is a promising method for this purpose. To illustrate the effectiveness of this method, first-principles molecular dynamics simulation has been applied. Technical issues of the simulation are described in detail. It is seen that resonant effects can be reproduced in adiabatic molecular dynamics simulations by applying an external force on the impurity only. The present study forms the basis for further developments of this approach.

Isotope dependence of the lifetime of the vibration of oxygen in silicon

By simply changing the isotopes of the Si atoms that neighbor an oxygen Oi atom in crystalline silicon, the measured decay rate tau of the asymmetric-stretch vibration (nu3=1136 cm-1) of oxygen (Oi) in silicon changes by a factor of approximately 2.5. These data establish that nu3 decays by creating one nu1 symmetric-stretch, local-vibrational mode of the Si-Oi-Si structure. If the residual energy (nu3-nu1) is less than the maximum frequency num of the host lattice, as for 28Si-16O-28Si in natural silicon, then it is emitted as one lattice mode, and tau depends on the density of one-phonon states at nu3-nu1. If (nu3-nu1)>num, as for 16O in single-isotope 30Si silicon, two lattice modes are created in addition to nu1, increasing tau. Prediction of tau for a particular defect clearly requires a detailed knowledge of that defect.

Vibrational lifetimes and frequency-gap law of hydrogen bending modes in semiconductors

Vibrational lifetimes of hydrogen and deuterium related bending modes in semiconductors are measured by transient bleaching spectroscopy and high-resolution infrared absorption spectroscopy. We find that the vibrational lifetimes follow a universal frequency-gap law; i.e., the decay time increases exponentially with increasing decay order, with values ranging from 1 ps for a one-phonon process to 265 ps for a four-phonon process. The temperature dependence of the lifetime shows that the bending mode decays by lowest-order multiphonon process. Our results provide new insights into vibrational decay and the giant isotope effect of hydrogen in semiconductor systems.