Abstract: A semiconductor radio-frequency power detector comprises, in a stack, an ohmic contact layer, undoped layer of a first semiconductor material, such as GaAs, of thickness l.sub.1, an undoped layer of a second semiconductor material, such as AlGaAs, of larger band gap than the first semiconductor material, the thickness of the layer being such that transport in the layer is primarily by intraband tunnelling, a second undoped layer of the first semiconductor material of thickness l.sub.2, where l.sub.2 >20l.sub.1, and a second ohmic contact layer. The difference between the thicknesses of the layers of the first semiconductor material gives rise to asymmetry in the current density/applied voltage characteristic for the device. An n+ layer may be incorporated in the second layer of the intrinsic first material to reduce "band bending" and to increase the current density.

Abstract: A Gunn effect oscillator comprises a body of semiconductor material in which electrons are injected from one region to another region via a very thin intervening system. The thin region has a thickness which is less than the mean free electron path length and is typically of the order of 100 .ANG., which results in hot electrons being transferred from the injection region into the other region in which electron bunches form.

Abstract: A semiconductor device comprises two layers of semiconductor material each of different conductivity type, with a region of semiconductor material sandwiched between the layers. The material of which the region is formed is of the same composition as the first layer at the edge of the region adjacent to the first layer, and varies in composition linearly on the running average in the direction between the layers such that the region forms a heterojunction with the second layer.