Plasma and transit-time mechanisms of the terahertz radiation detection in high-electron-mobility transistors

Abstract

We develop a device model for a high-electron-mobility transistor (HEMT) affected by the incoming terahertz radiation. The model takes into account the electron plasma oscillations in the HEMT channel, tunnelling of electrons from the channel into the gate layer and electron transit-time effects in this layer. It is shown that the excitation of plasma oscillations accompanied by the delay in the electron propagation across the gate layer and a strong nonlinearity of the tunnelling current can result in significant features of the HEMT high-frequency linear and nonlinear characteristics. We derive a formula for the HEMT gate-to-source/drain admittance. We also calculate the variation of the dc current induced by the terahertz radiation and the HEMT detection responsivity. It is found that the detection responsivity exhibits sharp resonant peaks corresponding to the frequencies of plasma oscillations. The resonant plasma frequencies and the positions of the admittance and detection responsivity peaks depend on the gate length and the lengths of the contact regions (source-to-gate and gate-to-drain spacings) and can be tuned by the gate voltage. The coincidence of the plasma and transit-time resonances can lead to a marked sharpening of the responsivity peaks.

Plasma oscillations in high-electron-mobility transistors with recessed gate

“…The latter dependence coincides with that calculated previously. 9,10 It is instructive that, as seen from Figs. 6 and 7, the fundamental plasma frequency is more sensitive to variations of the cap length than to variations of the window length.…”

“…The effect of the window ͑ungated͒ regions of the channel on the plasma spectrum in HEMTs was recently considered theoretically. 9,10 As shown, the window regions of the channel decrease the resonant plasma frequencies associated with the oscillations of the electron density and electric field mainly in the gated section of the channel. In HEMTs with the recessed gate used in experiments on the plasma oscillations excitation, the portions of the channel under the highly doped and, therefore, highly conducting cap layers can also play an important role in the net plasma spectrum because the latter is determined by the electron system in all portions of the channel.…”

Plasma wave resonant detection of femtosecond pulsed terahertz radiation by a nanometer field-effect transistor

“…In the saturation region hot electron physics might play an essential role. In particular, transit time effects, 18 interaction with optical phonons, 19 and/or stratification of electron flow 20 might enhance the resonance by diminishing the plasma wave decay. A detailed analysis of the transit time effects will be published elsewhere.…”

Nanometer transistors for emission and detection of THz radiation

“…This constant value of the voltage drop may indicate importance of the gate current at the onset of plasma instability. Such possibility was considered theoretically by Satou et al [28].…”