Quasi-magnetic fields revisited: second-order transport effects in graded semiconductors

When Kroemer (1957) introduced the concept of quasi-electric fields to describe the effects of graded semiconductors on carrier transport, he also discussed a "quasi-magnetic field" effect which occurs if the energy-band minimum shifts within the Brillouin zone as the alloy composition is varied. As heterostructure technology has developed in the subsequent forty years, such behavior of the energy-band structure has not been observed, and the quasi-magnetic field concept has largely been forgotten. However, a careful rederivation of the heterostructure drift-diffusion equation from the Boltzmann transport equation has revealed another quasi-magnetic field effect of the second order.