###### 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. c 202  
of a common substrate could also offer a more compact footprint, simplified testing, and reduced costs [3; 4]. The architecture of OEI circuits and systems varies across application types and can rapidly become complex. The need for a co-design and verification infrastructure for such systems capable of supporting billions of devices has therefore become imperative. In addition, co-design is highly dependent on the accuracy of compact models of each block. The compact models are in fact complete physical models converted into simpler and easy-to-solve analytical equations through reasonable assumptions and approximations. These models are commonly transcribed into programming languages such as Verilog-A, compatible with SPICE circuit design tools and software (Cadence, Mentor Graphics, etc.). In electronics, compact models have already reached a significant degree of maturity and computational efficiency over the last few decades. To enable design of high-speed integrated communication technologies, the photonics community has also started to develop compact models for optoelectronic devices, in order to unify electrical, photonic, and electromagnetic modeling using the same existing software design tools [5; 6; 7]. It is important to note that a scalable compact model offers two-fold benefit. At the device level, a scalable compact model is a powerful tool for predicting performances for varying device geometries, it also provides quick feedback on the impact of each technological and physical parameter. At the circuit/system level, compact models enable optimization of bias points and interconnections between photonic and electronic components, providing guidelines for predicting the performances of new OEIC designs. One of the key components capable of bridging these two worlds of optics and electronics is a photodiode. It allows to recover the information carried by an optical signal in the form of electrical information. There are several photodiode technologies such as conventional PIN photodiodes and avalanche photodiodes. The uni-traveling carrier photodiodes (UTC-PD) represent the most promising one. In particular, UTC-PDs have been widely studied for ultrafast optoelectronic applications, especially for the generation of THz signals [8]. High performances have been reported demonstrating bandwidths of more than 600 GHz reached with good power levels [8]. By relying mainly on electron transport, this architecture significantly improves the bandwidth and the power of the UTC-PDs compared to the conventional PIN photodiodes. As a result, UTC-PDs have become a key element in the convergence of electronic and photonic technologies in the millimeter wave band [9; 10].