The performances of GaAs-based Gunn diodes with a notch-δ-doped structure have been studied in this work. The δ-doped effect has been analysed using Monte Carlo modelling in terms of temporal evolution of current density, electric field profile, electron energy, mean velocity, and occupancy in Γ and higher valleys. The presence of a δ-doped layer after the notch caused a significant increase in the harmonic current amplitude of the device, where the growth of high field domain can be attributed to a slow electron track due to the well-known Gunn effect and an additional fast electron track which appears over a short time window when the domain is reaching the anode. An optimised GaAs notch-δ-doped structure with 700 nm device length including 100 nm notch and 5 nm δ-doped layer can generate signals at fundamental frequency of 262 GHz with a current harmonic amplitude of 29.4×107 A/m2, which is almost twice of that without δ-doped layer. Its second and third harmonic signals are found substantial reaching into the THz range of 512 GHz and 769 GHz.
In this work, Monte Carlo simulation is performed for InP Gunn diode with a notch-d-doped structure. It is found that the presence of the d-doped layer has improved the Gunn diode performance significantly as compared to the conventional notch structure. The d-doped effect caused an increment in the fundamental operating frequency and current harmonic amplitude in InP Gunn diodes by modifying the electric field profile within the device. An InP notch-d-doped Gunn diode with device length of 800 nm under 3V DC bias is capable of producing AC current signal of 287 GHz, reaching the THz region, with its harmonic amplitude being 5.68×108 A/m2. It is observed that InP-based notch-d-doped Gunn diode is able to generate signals at a higher operating frequency with a larger output power as compared to that of GaAs due to the higher electron drift velocity and threshold field in InP material.
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