Accurate equivalent circuit model for millimetre-wave UTC photodiodes

Abstract

We present a comprehensive study of uni-travelling carrier photodiode impedance and frequency photo-response supported by measurements up to 110 GHz. The results of this investigation provide valuable new information for the optimisation of the coupling efficiency between UTC-PDs and THz antennas. We show that the measured impedance cannot be explained employing the standard junction-capacitance/series-resistance concept and propose a new model for the observed effects, which exhibits good agreement with the experimental data. The achieved knowledge of the photodiode impedance will allow the absolute level of power emitted by antenna integrated UTCs to be predicted and ultimately maximised.

Accurate modelling and measurement of the impedance match between UTC photodiodes and THz antennas

“…We propose a new circuit model (Fig. 1), to explain the observations [5], that achieves very good agreement with the measurements. A link is suggested between the additional energy storage circuit elements present in the new circuit and quantum mechanical effects taking place between the UTC absorption and collection layers (i.e.…”

High performance waveguide uni-travelling carrier photodiode grown by solid source molecular beam epitaxy

“…The 2 μm fine features were achieved by RIE processing. The antenna impedance had been designed to realise complexconjugate matching to the UTC-PD in [27] at a frequency of 250 GHz. The total power emitted by an antenna depends on the impedance match with the driving source and the radiation efficiency.…”

“…The total power emitted by an antenna depends on the impedance match with the driving source and the radiation efficiency. The absolute level of power emitted by an antenna over the frequency range can be calculated and predicted if the UTC impedance is known and the coupling efficiency between UTC and antenna taken into account [27] [28]. We presented a comprehensive study of UTC-PD output impedance and frequency photoresponse in [27].…”

“…The absolute level of power emitted by an antenna over the frequency range can be calculated and predicted if the UTC impedance is known and the coupling efficiency between UTC and antenna taken into account [27] [28]. We presented a comprehensive study of UTC-PD output impedance and frequency photoresponse in [27]. The use of a Silicon lens combined with antenna integrated UTC-PDs is an established solution to couple THz power into free space [29].…”

“…In future work this issue can be addressed by applying an index matching layer to the lens surface. By means of 3d full-wave modelling and using the knowledge of UTC impedance [27] [28], we have calculated the absolute level of power emitted by our antenna integrated UTCs with Si lenses, as shown in Fig. 22, for 10 mA and 13.5 mA photocurrent.…”