Isotope Shifts in the Ground State of Shallow, Hydrogenic Centers in Pure Germanium

Large isotope shifts in the ground state of an acceptor $A_2$ ($E_{\mathrm{val}}+11.31\mathrm{}$ meV) and a donor $D$ ($E_{\mathrm{cond}}-12.34\mathrm{}$ meV) have been observed for the first time with photoelectric spectroscopy in pure germanium. The shifts ($\Delta E^{A_2}=+21\mathrm{}\pm 3$ μeV; $\Delta E^D=-51\mathrm{}\pm 3$ μeV) occur in germanium crystals grown in deuterium instead of hydrogen. $A_2$ and $D$ are observed at concentrations < 4×${10}^{11}$ ${\mathrm{cm}}^{-3\mathrm{}}$. The isotope shift is a direct proof that the centers $A_2$ and $D$ contain hydrogen.