We report on the response characteristics of plasmonic terahertz field-effect transistors (TeraFETs) fed with femtosecond and picosecond pulses. Varying the pulse width (tpw) from 10-15 s to 10-10 s under a constant input power condition revealed two distinctive pulse detection modes. In the short pulse mode (tpw << L/s, where L is the gated channel length, s is the plasma velocity), the source-to-drain voltage response is a sharp pulse oscillatory decay preceded by a delay time on the order of L/s. The plasma wave travels along the channel like the shallow water wave with a relatively narrow wave package. In the long pulse mode (tpw > L/s), the response profile has two oscillatory decay processes and the propagation of plasma wave is analogues to oscillating rod with one side fixed. The ultimate response time at the long pulse mode is significantly higher than that under the short pulse conditions. The detection conditions under the long pulse mode are close to the step response condition, and the response time conforms well to the analytical theory for the step function response. The simulated waveform agrees well with the measured pulse response. Our results show that the measurements of the pulse response enable the material parameter extraction from the pulse response data (including the effective mass, kinematic viscosity and momentum relaxation time).
TeraFET terahertz detectors with spatially non-uniform gate capacitances
太赫兹场效应晶体管（TeraFET）沟道中的非均匀电容分布可以显著提高太赫兹探测性能。对于指数变化的电容与距离的流体动力学方程的解析解和模拟显示，130 nm Si TeraFET的响应度增加了约10%，与数值模拟非常一致。使用流体动力学方程的数值解，我们比较了三种不同的Cg配置（指数，线性和非线性）。仿真结果表明，该配置提供了最大的响应可调性。我们还比较了Si，III-V和p-金刚石TeraFET的非均匀电容分布的影响。结果证实了p-金刚石在太赫兹应用中的巨大潜力。改变跨沟道的阈值电压可以具有与改变栅极到沟道电容类似的效果。THz检测性能的改进背后的物理学与通过组成不对称的器件几何形状打破通道对称性有关。
