The dissertation is devoted to the development of an advanced germanium p-i-n photodetector for modern laser rangefinders and sensor-measuring devices at a wavelength of 1.54 μm, which is safer for the human eye compared to 1.06 μm used in modern rangefinders. The design and technology of manufacturing a reliable, high-speed and highly sensitive Ge p-i-n photodiode, which is protected by a patent for the invention of Ukraine, has been developed and the prospects of its application have been experimentally shown.
The current problem of existing germanium p-i-n photodiodes that needs to be solved is low reliability and their high degradation over time. This problem is associated with the use as passive layers - SiO2, Si3N4, ZrO2, or cubic zirconia, the constant lattice and the coefficient of thermal expansion of which differs significantly from Ge, resulting in a large number of dislocations and defects. The idea of increasing the reliability of Ge p-i-n photodiode was proposed due to the use of zinc selenide (ZnSe) as a passivating coating. This material has a coefficient of thermal expansion, which is 6.1x10-6 K-1, as close as possible to the corresponding figure for germanium - 7.1x10-6 K-1. The reduction of surface currents is achieved due to the large band gap of 2.7 eV ZnSe, compared with its own Ge 0.67 eV. ZnSe has a high transparency in the IR range of radiation, so it can be applied to both the front surface of the photodetector and the side surface to protect the p-n junction. The paper experimentally proves that the passivation of the Ge p-i-n photodiode with ZnSe allowed to achieve an improvement in its characteristics and reliability.
The scientific novelty of the obtained results is as follows:
1. For the first time, a new passivating coating was proposed to protect the Ge mesostructure of the photodetector - the polycrystalline ZnSe layer, which, unlike existing coatings, provides: high matching of crystal lattices (99.8%) and linear thermal expansion coefficient ~ 7 · 10–6 deg – 1 for ZnSe and ~ 6 · 10–6 deg – 1 for Ge). These advantages allow to reduce the level of mechanical stresses of the surface layer and the associated concentration of dislocations and defects, which ensured the absence of degradation of the photodiode for 3 years from the date of manufacture in 2018 to 2021.
2. Simulation and theoretical calculations of the energy structure of the developed Ge p-i-n photodiode and its spectral sensitivity are performed. The simulation results were confirmed by measurements on experimental samples with an error of ± 0.01 A / W. Studies have confirmed the possibility of using a theoretical model to achieve the required band structure of the photodiode and optimize its design.
3. The influence of the ZnSe / Ge phase composition on the electrical resistance of the ZnSe passivation layer was established for the first time. For this purpose, a method of measuring the electrical resistance of high-impedance thin films using elastic contacts was developed, which has the following advantages over the Van der Pauw method: low pressure on the semiconductor surface, large contact area and as a result heating.
The practical significance of the results is as follows:
1. For the first time, an advanced high-reliability Ge p-i-n photodiode has been developed, which has the parameters required for photodetectors as part of a pulsed laser rangefinder and has a relaxation time of 5.8 10-8 s and a sensitivity at λmax = 1.54 μm 0.45 A/W. Scientific and technical solution is protected by the patent of Ukraine for the invention/
2. The prospects of the improved Ge p-i-n photodiode as a part of the model of a pulsed laser rangefinder are experimentally proved. This photodiode has sufficient speed to reliably record short pulses of about 20 ns. The total transmittance of light filters that attenuated the laser pulse (Es = 578 μJ) was kf1-4 = 0.000437, which is an order of magnitude higher than the theoretically calculated transmittance at a measured distance of 5 km (katm = 0.0038) and meets the technical requirements to the photodiode in the pulsed laser rangefinder.
3. The prospects of application of the developed Ge p-i-n photodiode as a part of the model of the device on the basis of the phenomenon of surface plasmon resonance working in the near infrared range of the spectrum are shown. The results of the study confirmed the prospects of using the developed Ge p-i-n photodiode in the measuring device based on the phenomenon of surface plasmon resonance with sensitivity.
The results of research conducted in this work are promising for use in industry and research. The results of the research are confirmed by the relevant acts of implementation of the Institute of Single Crystals of the National Academy of Sciences of Ukraine and the Institute of Semiconductor Physics. V.Ye. Lashkareva National Academy of Sciences of Ukraine.
