Experimental evidence on the band structure of germanium and silicon

Synopsis This paper reviews the status of experiments bearing on the band structure of semiconductors, with particular reference to germanium and silicon. The situation in n-Ge is especially clear, as both cyclotron resonance and magnetoresistance experiments show that the energy surfaces at the bottom of the conduction band are prolate spheroids oriented along the [111] directions in k-space; the spheroids are highly anisotropic, with a mass ratio of about 15:1. In p-Ge the two isotropic lines in cyclotron resonance suggest that the band edge is at the center of the Brillouin zone; the multiplicity is explained by spin-orbit splitting. It appears that this model may account, qualitatively for the remarkable infra-red absorption of p-Ge, but it seems to be difficult to explain transport data. From magnetoresistance and from cyclotron resonance it is found that the energy surfaces in n-Si are prolate spheroids directed along [100] axes, while the structure of p-Si is like p-Ge.