## 1 Introduction  
The field of silicon photonics (Si PDs) is nowadays an emerging market promising to reach a value of more than $4 billion in the 2024 as shown in Figure 1. Indeed, both switching and interconnects of the existing data center will no longer support the huge increase in internet data traffic driven by the social network and video contents. Figure 1: Silicon photonics 2013–2025 market forecast [1]. Reproduced with permission from [PERSON], Director, Public Relations at Yole Développement. This is because in the near future new technologies must be introduced. The research activity in Silicon photonics can be dated back to the 1980s and in recent years more and more players are emerging in this industry's landscape. Nowadays, Intel shares the leadership in this field with Luxtera, with products for 100 G data rates already present on the market. As Silicon (Si) is a mature technology developed during the years of the strong expansion of the microelectronic industry, the use of Si for the fabrications of photonic components meet the requirements of the data center in term of low cost, reliability, integration density and power consumption. A key component in Si photonics is constituted by the photodetectors (PDs), devices that are able to convert the incoming light into current. Si PDs are commercial devices in the visible spectrum, however, the employment of Si for the realization of PD operating at near-infrared (NIR) wavelengths is not a simple task due to Si transparence above 1.1 \(\upmu\)m. NIR Si PDs take conventionally advantage of germanium (Ge) integration [2; 3] on Si, however, due to a 4.3% lattice mismatch, very high leakage current hinders the device performance. This issue can be mitigated by realizing a buffer layer based on a two-step epitaxial growth technique [2; 3] that minimize but, unfortunately, do not remove the defect center responsible of the high leakage current. Moreover, this buffer layer generates some problems in terms of thermal budget and planarity [4] preventing the possibility of a monolithic Ge integration on Si. In addition, Ge is characterized by a low absorption at 1550 nm with respect to gallium arsenide (InGaAs) leading to thick active intrinsic region of the PIN structures and slow devices. In this context, an all-Si approach is preferred, and one option for detecting NIR wavelengths is given by the internal photoemission effect (IPE). IPE occurs in a metal/semiconductor Schottky junction when, due to an incident optical radiation, the carriers of the metal are excited to energies above the Schottky barrier of the junction and transported in the conduction band of the semiconductor [5; 6]. IPE has been widely used in high-performance platinum silicide (PtSi) and palladium silicide (Pd\({}_{2}\)Si) Schottky barrier infrared charged coupled devices (CCDs). The first generation of detectors were based on a Pd2 Si/Si Schottky junctions and were developed for operating in the spectrum from 1 to 2.4 \(\upmu\)m for satellite applications and it required an operating temperature of 120 K [7; 8]. Subsequently, PtSi/Si Shottky junctions showed the capability to work at longer wavelengths, from 3 to 5 \(\upmu\)m [9; 10]. The 512 \(\times\) 512 focal plane array based on PtSi requires an operating temperature of 80 K [11]. In these devices, due to the low Schottky Barrier Height (SBH), the cryogenic temperature was necessary to minimize the noise current. In 2006, it was proposed that higher SBH should be worked with in order to use IPE at room temperature and to recover the consequently reduced efficiency by means of Fabry-Perot resonant structures [12]. Subsequently, not only these devices were realized [13] but many other strategies were employed in order to increase the efficiency of IPE-based Si PDs at room temperature. Indeed, IPE was investigated in metallic structures at nanoscale as: Si nanoparticles (NPs) [14], stripes able to support surface plasmon polaritons (SPPs) [15; 16], gratings [17] and antennas [18].