Band Structure
A characteristic feature of the valence band in many cubic semiconductors is the convergence of the heavy hole and light hole energy bands at the zone center. This quantum mechanical phenomenon is known as heavy hole band degeneracy and determines the density of states in the material. The overlapping states increase the effective mass of the charge carriers.
Carrier transport is consequently influenced in p-type semiconductor substrates.
Mechanical Stress
Anisotropic strain breaks the symmetry of the crystal lattice and separates the energy levels of the two bands. This physical deformation resolves the heavy hole band degeneracy by splitting the valence band. Silicon diaphragms in piezoresistive pressure sensors utilize this mechanism to achieve high sensitivity.
Sensing Consequence
Sensing sensitivity fluctuates when the splitting of the energy levels varies with temperature or applied force. The separation of these states directly affects the hole mobility and the piezoresistive coefficient. Designers monitor this variation to predict sensor performance under extreme environmental conditions.
Calibration Challenge
Measurement drift occurs when residual stress from packaging alters the band splitting over time. Testing protocols must account for the heavy hole band degeneracy variation during thermal cycling. This behavior establishes the long-term stability boundary of the piezoresistive transducer.
