Characteristics of a terahertz photomixer based on a high-electron mobility transistor structure with optical input through the ungated regions

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Abstract
We develop a device model for a terahertz photomixer that utilizes the excitation of plasma oscillations in the channel of a device similar to a high-electron mobility transistor (HEMT). The device design assumes vertical optical input through the ungated source–gate and gate–drain regions. Using this model, we calculate the characteristics of the HEMT photomixer: the responsivity as a function of the signal frequency for devices with different geometrical and physical parameters, and the dependence of resonant frequency on the length of the gated and ungated portions of the channel and the gate voltage. We compare also the performance of the HEMT photomixer with that of a similar device but one in which the optical input is through the substrate.