# Understanding the Light Detection in an Integrated Novel Electrophotonic Wavesensor Photodetector
## 1 Introduction  
Seamless silicon integrated electrophotonics is the combination of electronic and photonic devices to produce a monolithic circuit which simultaneously controls and manipulates both optical and electronic signals. There are three basic elements considered the bare minimum to obtain an electrophotonic circuit: light emitters in silicon, waveguides compatible with silicon technology, and silicon photodetectors [1; 2]. In the past few years, the development of silicon light sources has advanced significantly, and integration of such devices into electrophotonic circuits has been demonstrated [3; 4; 5; 6; 7; 8]. However, one of the major challenges to tackle remains the improvement of their relatively low light emission powers [9; 10; 11]. One of the most promising silicon compatible light sources reported is the Light Emitting Capacitor (LEC), which uses Silicon Rich Oxide (SRO) as an active light emission layer [12; 13; 14; 15]. The light emission of the SRO-based MOS-like structures ranges from the visible to the near infrared, and they are completely integrable with existing photonic elements based on silicon nitride (Si\({}_{3}\)N\({}_{4}\)). Most importantly, their fabrication is fully compatible with MOS processes. Due to its broad spectrum within the visible range, this kind of light sources can be suitable for chemical or biological sensors. However, they present the disadvantage of the mentioned low emission power as compared to other external light sources, such as externally coupled lasers. Despitethis, SRO-based LECs have been successfully used in electrophotonic chips, and the light has been transmitted across the nitride waveguide and detected by an integrated silicon photodiode in the same silicon chip [5]. Other technologies, such as silicon on insulator use lasers and sensors made of Si-Ge, InGaAs, III/V and other materials that do not have such light power limitations, but they are not compatible with MOS technologies, and consequently, it is not possible to monolithically integrate in silicon electronics [9; 16; 17]. On the matter of light transmission, photonic devices are currently available in different foundries, including waveguides and other photonic devices [18; 19; 20]. A particularly interesting material for light guiding is Si\({}_{3}\)N\({}_{4}\), as it is fully compatible with CMOS processes, it presents good transmission for visible and NIR light, and its refractive index in such range has enough contrast with air and silicon dioxide to obtain adequate confinement [21; 22; 23]. In addition, Si\({}_{3}\)N\({}_{4}\) has been successfully coupled to LECs, and it has even been coupled to photodetectors to obtain complex integrated sensors [5; 24]. Regarding photodetectors, up to now silicon photodiodes have been the main choice for seamless electrophotonic integrated circuits [4; 8; 16]. The monolithic integration of LECs, nitride waveguides, and silicon planar photodetectors is possible in CMOS technology, and all the elements are auto-coupled to each other, which is an unprecedented advantage. However, distributed electrophotonic functions along the chip will require better light detection capabilities, due to the mentioned relatively low light intensity emitted by LECs, which is in the range of nanowatts [11]. For example, developing integrated systems as lab-on-a-chip will require the simultaneous interaction between light and both chemical and biological elements, a difficult task for such low powers. Then, as an alternative to higher power light sources, which present lower compatibility for integration, we propose the development of more adequate electrophotonic sensors to counteract this limitation by the emitter, as the presently existing photodetectors are not developed within the intimate integration philosophy that electrophotonics offer [25]. The use of the traditional architecture of silicon photodiodes presents some disadvantages in this respect, such as the light passing across a heavily doped layer before photons can reach the active depleted zone.