  Isotopic enrichment offers cutting-edge properties of materials opening
exciting research and development opportunities. In semiconductors, reached
progress of ultimate control in growth and doping techniques follows nowadays
the high level isotopic purification. This requires deep understanding of
isotopic disorder effects and techniques of their effective determination.
Isotopic content of both crystal lattice and impurity centers cause the
effects, which can be examined by different optical techniques. While disorder
in the host lattice can be straight forward evaluated by inelastic light
scattering or by SIMS measurements, determination of isotopic contributions of
many orders less presented impurities remains challenging and usually observed
in high-resolution photoluminescence or optical absorption spectra. Boron-doped
diamonds exhibit complex infrared absorption spectra while boron-related
luminescence remains unobserved. Boron, as a most light element acting as a
hydrogen-like dopant in elemental semiconductors, has a largest relative
difference in its isotope masses, and by this, cause the largest isotopic
disorder in semiconductors, including diamond, an elemental semiconductor with
the lightest atomic mass of a host lattice. This enables an access to the
isotopic constitution of boron in diamond by infrared absorption spectroscopy.
By comparison of low-temperature absorption spectra of a natural (20% of 10B
and 80% of 11B isotopes) and 11B enriched (up to 99%) doped diamonds we
differentiate the intracenter transitions related to 10B and to 11B isotopes.
We have found that the isotopic spectral lines of the same boron intracenter
transition are separated with the energy of about 0.7 meV. This is the largest
impurity isotopic shift ever observed in semiconductors doped by hydrogen-like
impurity centers.
