The differential dc and hf conductivities of semiconductor superlattices with various electron miniband dispersion relations are studied. It is shown that, due to the anharmonicity of Bloch oscillations, the hf conductivity can be negative at frequencies equal to integral multiples of the Bloch frequency. This effect can arise even in the regions where the differential dc conductivity is positive. The results of the study suggest that superlattices with a miniband dispersion law in which the effective electron mass is positive in a sizable part of the miniband and decreases as the electron energy increases can be used to generate and amplify terahertz-range (microwave) fields.
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Romanov et al. (2004) studied this question.
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