Multiscale Compact Modelling of UTC-Photodiodes Enabling Monolithic Terahertz Communication Systems Design

Abstract

Due to the continuous increase in data traffic, it is becoming imperative to develop communication systems capable of meeting the throughput requirements. Monolithic Opto-Electronic Integrated Circuits (OEICs) are ideal candidates to meet these demands. With that in mind, we propose a compact and computationally efficient model for Uni-Traveling Carrier Photodiodes (UTC-PDs) which are a key component of OEICs because of their high bandwidth and RF output power. The developed compact model is compatible with existing SPICE design software, enabling the design of beyond 5G and terahertz (THz) communication circuits and systems. By introducing detailed physical equations describing, in particular, the dark current, the intrinsic series resistance, and the junction capacitance, the model accurately captures the physical characteristics of the UTC-PD. The model parameter extraction follows a scalable extraction methodology derived from that of the bipolar and CMOS technologies. A detailed description of the de-embedding process is presented. Excellent agreement between the compact model and measurements has been achieved, showing model versatility across various technologies and scalability over several geometries.

Wideband Type-II GaInAsSb/InP Uni-Traveling Carrier Photodiodes for Near 300 Gbps Communications

“…We previously reported an equivalent circuit model of our UTC-PDs, showing a resistive and capacitive behavior of the devices up to 67 GHz. The CPW pads are designed so that the elements of the equivalent circuits of the OPEN and SHORT test structures are independent of the frequency up to 67 GHz and, thus, do not affect the normalized RF device response below 67 GHz [19]. However, for higher frequencies, the On completion of the measurements, both measured and fitted photoresponses are normalized to the near DC (0.2 GHz) value to obtain the normalized response curves plotted in Fig.…”

“…In parallel to the junction capacitance, the transconductance of the voltage-controlled-current-source (VCCS) is used to tune the absolute response (power) level for different device sizes. To model the behavior of the pad parasitics up to 110 GHz, three different LC sections were added to the circuit model, as shown in Fig.4(b)[19]. The first section, L ab and C ab , represents the parasitic behavior of the mesa bridge with Teflon underneath.…”

SPICE Modeling in Verilog-A for Photo-Response in UTC-Photodiodes Targeting Beyond-5G Circuit Design

“…Moreover, the simplicity of the existing equivalent circuit models limit their accuracy compared to analytic equations describing the physics of UTC-PDs [10][11][12]. In an effort to bring SPICE models closer to the physical transport mechanisms, a comprehensive SPICE model in Verilog-A, which accounts for both static and dynamic behavior of UTC-PDs, was presented in [13] and further detailed in [14][15]. However, due to the inherent complexity in implementing the analytical equations describing the photoresponse in Verilog-A, behavioral approximations were used that limit the model's physical basis as well as its accuracy at higher frequencies.…”

“…The photocurrent is controlled by the input optical power and is modelled by the photo-generation rate and the transfer functions in the absorber and collector regions. While the Verilog-A model presented in [13][14][15], captured both the static and dynamic behavior of UTC-PDs quite well, the dynamic photocurrent modeling remained rather simplified. This is because the implementation of the complete analytical form is not straightforward due to the complex sinc and exponential functions representing its frequency dependence.…”

“…3-dB cut-off frequency. To take this into account for model validation, we leveraged the UTC-PD SPICE compact model and associated parameter set without illumination (detailed in [14][15]) for the simulation of dynamic photo-response. Results are shown in Figs.…”