# Recent Advances in Si-Compatible Nanostructured Photodetectors
## 1 Introduction  
During the last century, light detection methods have improved significantly, from thermal detectors to photon detectors, focal plane arrays, and single-photon avalanche detectors [1]. Nowadays you can reach any piece of information in a matter of milliseconds, or even less, due to the technological developments that have happened in the past several decades. The world is now full of different technologies that have made our lives much easier. It is so easy to communicate using many different means from landlines to optical fibers and satellite communications. The more communication methods develop, the more secure and fast transmission technology is needed. This fact forces the scientific community to develop light-transmitting systems and these needs support a big interest in the light detection area. Currently, nanostructures with quantum wells (QW) and quantum dots (QD) are very widely used to create photodetectors in the visible and infrared ranges. At the same time, for various applications, various semiconductor material systems are used that most fully satisfy the specific requirements for device structures: III-V (GaAs, AlGaAs, etc. ), II-VI (CdHgTe), IV-IV (GeSi, GeSn, GeSiSn), and others. However, all their potentialities are not implemented so far and they remain one of the most promising structures for creating optoelectronic devices. A characteristic feature of all types of low-dimensional structures is the manifestation of the effects of spatial (dimensional) quantization, caused by the limitation of the free movement of charge carriers in one or several directions. Size quantization effects lead to a significant change in the energy spectrum of electrons and holes and the appearance of discrete energy levels and intermediate-allowed energy bands entirely located in the band gap of the semiconductor. This, in turn, leads to the appearance of new unique properties of such structures, which make it possible to create completely new types of optoelectronic devices on their basis [2]. For the first time, the existence of spatial quantization effects in low-dimensional semiconductor structures (nanostructures) was experimentally demonstrated by [PERSON] et al. in the first half of the 1970s when studying optical properties of AlGaAs-GaAs heterostructures with GaAs quantum well [3]. Germanium quantum dots in silicon becameone of the central themes of research in the early 1990s, when they were first obtained in the experiments by [PERSON], [PERSON] et al. [4; 5]. Almost immediately, quantum-well effects were observed experimentally in this system [6]. The main requirements for choosing photodetectors are good performance, operation at the highest possible temperatures, and low manufacturing costs. In addition, today it seems necessary to create on a single chip the entire set of components of fiber-optic communication lines, including light-emitting devices and photodetectors. To reduce the costs of such systems, it is necessary that a larger number of components be made on the basis of typical silicon technology methods. Silicon itself is transparent to radiation with a wavelength greater than 1.1 microns. Good photosensitivity in the region of \(\lambda\approx 1.5\)\(\upmu\)m is possessed by germanium photodetectors. The Ge/Si system may be also supplemented by tin, which extends the responsivity up to 2 \(\upmu\)m. In this regard, prospects are outlined for the creation of high-speed photodetectors based on Si-Ge-Sn heterostructures with high sensitivity at room temperature in the spectral range of quartz fiber transparency of 1.3 and 1.55 \(\upmu\)m.  
Besides that, the adding of tin provides an opportunity to control the lattice constant and energy gap independently. Among the other advantages of group-IV materials is the possibility to create multispectral detectors, rather high mobility of carriers, and fast-speed operation, along with low noise, simple design, and highly-developed technology of synthesis.