Analytic Model of Transit-Time Diodes and Transistors for the Generation and Detection of THz Radiation

An analytic model of low-dimensional transit-time diodes and transistors for the generation and detection of THz radiation in a linear approximation with respect to an alternating electric field is developed. Thin layers of silicon and arrays of nanowires are proposed as promising structures. It is shown that the presence of ballistic (without scattering) transport is sufficient in itself for the appearance of negative conductivity, which is necessary for the generation of radiation at frequencies of the order of the inverse transit time. In the presence of scattering, the appearance of negative conductivity has a threshold character depending on the scattering intensity. However, a variable injection from the contacts (BARITT effect) causes the appearance of negative conductivity even in the case of strong scattering. The analysis shows that in the structure proposed by us the effect of the variable injection can be strong, especially when introducing an additional electrode (gate) from which an alternating current is transmitted to the antenna. In this case, a highly efficient conversion of the dc current to terahertz oscillations is provided. It is shown that the effect of the variable spatial charge on the operation of the considered structures of the transit diodes can be neglected. This justifies the proposed analytic model. The rectifying properties of the structures under study can be used as the basis for detecting THz radiation.