Electron dispersion relations with negative effective masses in quantum wells grown on the cleaved edge of a superlattice

Engineered energy-wave-vector dispersion relations of either electrons or holes hold great promise for realizing fundamental oscillators at terahertz frequencies if they contain sections with a negative effective mass (NEM) at appropriate energy levels. However, neither bulk semiconductor materials nor quantum wells or quantum wires exhibit such NEM sections in the dispersion relations at favorable energy levels. Therefore, the novel use of a nanostructure is proposed to create an NEM section of electrons at suitable energy levels. This structure utilizes a heterojunction with a quantum well (QW) channel grown perpendicular to a superlattice. At small values of the wave-vector k, the electron wave function Ψ resides mostly in the QW channel and, as k increases, Ψ extends further into the superlattice. This spread of Ψ induces an NEM section in the energy dispersion relation E(k). Several combinations of suitable material systems are considered.