Zero valley splitting at zero magnetic field for strained Si/SiGe   quantum wells grown on tilted substrates
  The electronic structure for a strained Si/SiGe quantum well grown on a tilted substrate with periodic steps is calculated using a parameterized tight-binding method. For a zero tilt angle the energy difference between the two lowest minima of the conduction band at the center of the Brillouin zone defines a non-zero valley splitting. At finite tilt angles, the two lowest conduction band minima shift to k0 and -k0 in the Brillouin zone and have equal energy. The valley splitting for quantum wells grown on a tilted substrate is therefore equal to zero, which is a direct consequence of the periodicity of the steps at the interfaces between the quantum well and the buffer materials. 
Paul von Allmen and Seungwon Lee