Abstract
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.
Highlights
To meet the bandwidth, power, and gain demands of highspeed wireless communication systems [1], [2], new semiconductor technologies that can operate at frequencies exceeding 300 GHz, while delivering output power on the order of a Watt within a compact form-factor are highly sought after [3]
Our study focuses on the modeling of the transport of optically excited charge cloud in a Gallium Nitride (GaN) photoconductive semiconductor switch (PCSS) for a wide range of optical bias and device geometry parameters
Our analysis conclusively shows that we can simultaneously achieve pulse compression and increase in the peak output current when the DC electric field across the GaN PCSS leads to negative differential mobility (NDM)
Summary
Power, and gain demands of highspeed wireless communication systems [1], [2], new semiconductor technologies that can operate at frequencies exceeding 300 GHz, while delivering output power on the order of a Watt within a compact form-factor are highly sought after [3]. Our analysis conclusively shows that we can simultaneously achieve pulse compression (for higher bandwidth) and increase in the peak output current (for higher output power and power gain) when the DC electric field across the GaN PCSS leads to NDM. The results presented here can guide experimental investigations of near-THz GaN PCSS in which the electric field and optical bias can be simultaneously engineered to benefit from the intrinsic NDM phenomenon. Such theoryguided experimental investigations of pulse compression in semiconductors with the NDM phenomenon are currently underway and will be reported elsewhere. An appendix is included to contrast the response of the PCSS with and without the NDM effect
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