On the role of negative effective masses in the formation of the conductivity of semiconductor superlattices

The conditions for forming static and high-frequency negative conductivities of semiconductor superlattices with different fractions of the region of negative effective mass in the miniband are investigated. It is demonstrated that a decrease in the negative-mass fraction leads to broadening of the regions of both the negative differential and negative absolute conductivities of superlattices and to the occurrence of additional harmonic-field instability regions. The development of static instability in a superlattice arranged in an open external dc current circuit can result in the generation of both integrally and fractionally quantized static fields.