Study On Properties Of Amorphous Silicon Carbide And Amorphous Silicon Carbonnitride Antireflective Films

Silicon is a base material of modern microelectronics.For example,it is widely used to produce optical elements of IR optics.However,the largest area of silicon application is semiconductor solar power engineering where it is used to make photoelectric converters of solar energy-solar cells（SCs）.More than 90%of the world’s solar cells are made of silicon semiconductors,both monocrystalline and multicrystalline（polycrystalline with big crystallites-up to several cm）.One of the main ways to improve silicon SCs parameters is reduction of light reflection loss caused by high refractive index of silicon.In the infrared spectrum region with high silicon refractive index,the application of silicon also urgently needs to solve this problem.The above problem is solved by using antireflection coatings（ARCs）.At the same time,the ARCs for optical elements used in the IR spectral region must have protective functions,since an element is in direct contact with environment.Earlier studies have shown that coatings with the highest ratio of hardness to Young’s modulus H/E have higher durability,while environmental corrosion resistance is a more important requirement for anti-reflection and protective coatings.Double oxide coatings and single nitride coatings have good anti-reflection properties in optical communication systems operating in the near infrared spectrum region.Silicon nitride thin films with a thickness of about 0.20μm were prepared by plasma-enhanced chemical vapor deposition（PECVD）,and anti-reflection studies were carried out in the telecommunication window（1.310μm and 1.55μm）.In the work we demonstrated the possibility to apply amorphous non-stoichiometric silicon carbide(a-Si_xC_1-x:H)and silicon carbonitride(a-Si_xC_1-x-yN_y:H)films for improvement of exploitation characteristics of silicon-based photoelectric devices and optical elements in very wide spectral range—from UV to mid-IR.The a-Si_xC_1-x:H films possessing optical properties required for effective antireflection（AR）effects for silicon(refractive index（n）atλ=632 nm from 1.86 to 1.98,optical bandgap(E_opt)from 2.7 to 3.1 e V,and extinction coefficient（k）is close to zero practically in all spectral range)were obtained by PE-CVD from methane,silane,hydrogen,and argon gas mixture.To deposit silicon carbonitride films some amount of nitrogen was added to the gas mixture.For the a-Si_xC_1-x-yN_y:H films the following optical parameters were obtained:n=1.76–1.93,E_opt=3.1–3.4 e V,k～0.It has been shown that the proposed films possess unique mechanical properties and ratio of the films hardness to their Young modulus is very high（H/E>0.13）.It is evidence of the films high wear resistance that is of great importance when the films are used for protection of silicon optical elements in IR spectral range.It is established that the films of both types are very suitable as excellent AR coatings for silicon in the spectral range of Si-based solar cell photosensitivity,telecommunication windows,and mid-IR.Deposition of even single layer AR film allowed us to reduce reflection losses significantly（reflection coefficient（R）at minimum of reflection becomes close to zero）.As a result,efficiency of etched multicrystalline Si-based solar cell（SC）was significantly improved.Transmittance of Si-based optical elements with front and rear AR films reached practically 100%in the telecommunication windows spectral range.