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<p>The wide bandgap material, Gallium Nitride
(GaN), has emerged as the dominant semiconductor
material to implement high-electron mobility transistors
(HEMTs) that form the basis of RF electronics. GaN is also
an excellent material to realize photoconductive switches
(PCSS) whose high-frequency performance could exceed
that of RF HEMTs. In this paper, we numerically model
the output characteristics of a GaN PCSS as a function of
the input electrical and optical bias and the device dimensions. Importantly, we show that operating the GaN PCSS
in the regime of negative differential mobility significantly
benefits its high-frequency performance by compressing
the temporal width of the output current pulse, while also
enhancing its peak value. We find that when the optically
excited carriers are generated in the middle of the active
region, the bandwidth of the device is approximately 600
GHz, while delivering an output power exceeding 800 mW
with a power gain greater than 35 dB. The output power
increases to 1.5 W, and the power gain exceeds 40 dB
with a near-terahertz bandwidth ( ≈ 800 GHz), as the laser
source is moved closer to the anode. Finally, we elucidate
that under high optical bias with significant electrostatic
screening effects, the DC electric field across the device
can be boosted to further enhance the performance of the
GaN PCSS.
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Design and Simulation of Near-Terahertz GaN Photoconductive Switches--Operation in the Negative Differential Mobility Regime and Pulse Compression
