INTERVALLEY SCATTERING POTENTIALS OF GE FROM DIRECT EXCITON ABSORPTION UNDER PRESSURE

We have measured the dependence on pressure of the low-temperature (10 K) direct exciton optical absorption of Ge up to 12.3 GPa. rhe sharp exciton peak at the direct energy gap (E0) of Ge is found to broaden s ignificantly with increasing pressure. This effect, which is attribute d to intervalley scattering via electron-phonon interaction, is most p ronounced for pressures above approximately 0.6 GPa, where the X valle y becomes the lowest conduction-band minimum. From the pressure-induce d exciton broadening we determine the GAMMA to X point intervalley def ormation-potential constant D(GAMMAX)=2.2(3) eV/angstrom and an upper bound of D(GAMMAL) = 4.5 eV/A for scattering from GAMMA to the L valle ys. The deformation potential D(GAMMAX) of Ge is about 50% smaller com pared to isoelectronic GaAs. This difference is attributed to the fact that interatomic matrix elements between s and d states of the GAMMA and X conduction-band minima as well as the d character of the X minim um are larger in GaAs.