ROLE OF THE VALENCE-BAND DENSITY-OF-STATES IN THE PIEZORESISTANCE OF P-TYPE SEMICONDUCTORS SI AND GE

It has been shown that unusual hole concentration changes in p-type Si and Ge under stress reported in the earlier work are well accounted for in terms of density of states (DOS) change of each hole due to stress. The DOS of heavy-hole band decreases, while that of light-hole band increases near the band edge region for both tensile and compressive stresses, which impedes the carrier transfer and hence results in extremely small, nearly stress-quadratic hole concentration changes. It has also been demonstrated that, when these DOS changes overwhelm the carrier transfer effect, even the decrease of the low-energy heavy hole concentration takes place at low temperatures.