STUDY OF BALANCE-EQUATIONS FOR HOT-ELECTRON TRANSPORT IN AN ARBITRARYENERGY-BAND

In view of the recent disputes of Huang and Wu and Lei about Lei's bal ance equation theory for an arbitrary energy band, the balance equatio ns for hot-electron transport in an arbitrary energy band are reformul ated. In the new formulation the adoption of the effective Hamiltonian method is avoided and all calculations are carried out in laboratory coordinates. In the mean time the crystal momentum k is carefully dist inguished from the physical momentum. By introducing a correct equilib rium density matrix of the drifting electron gas in place of that used by Lei, the balance equations together with the distribution function can be derived directly with no need to distinguish the degree of fre edom of the center of mass from the relative degree of freedom of the electrons, which is in our opinion neither possible nor necessary at l east for a nonparabolic energy band. Some problems associated with the foundation of the balance equation theory are also examined. The resu lt shows that the comment to Lei's theory given by Huang and Wu is cor rect and to the point. Nevertheless, contrary to their assertion that this theory is inapplicable to the nonparabolic band transport, Lei's balance equations, after a few, however, important corrections, are st ill applicable to transport for nonparabolic energy bands.