THE ANALYSIS OF HIGH TEMPERATURE IMPACT ON EPITAXIC STRUCTURES AND CONTACT SYSTEMS FOR PHOTOELECTRIC TRANSDUCERS
Journal Title: Вісник Кременчуцького національного університету імені Михайла Остроградського - Year 2017, Vol 1, Issue 103
Abstract
Purpose. One of the major aims in the engineering of solar elements is increasing their efficiency. For effective transformation of solar radiation into electric energy due to the division of electron-hole pairs by internal electric field, the depth of stratification of the field, that separates them, should be sufficient for penetration of the main stream of photons. The analysis demonstrates, that the displacement to the short-waves spectrum increases the efficiency of energy transduction. However, in the conditions of reality, it is necessary to work in the spectrum close to infrared, i.e. of short waves. It can be explained by the fact, that the atmosphere is more transparent for them. To achieve that, the depth of the internal field stratification should be enlarged. In case the wavelength is less than 1,1 µm, photoelectric transducers are not sensitive to the photons stream, as far as their energy is not sufficient for generation of charge carriers. The problem of increasing of PET sensitivity can be solved by means of choosing of heterostructure SNS (semiconductor – nonconductor – semiconductor), that constitutes its fundamentals, and by means of application of high-quality contact systems. Methodology. The authors elaborated the contact system Al-Cu-Si, which is marked by increased stability to electro-migration and which prevents silicon erosion in contact windows simultaneously. The function of the backing was done by silicon plates of nn+ – type with resistivity 0,5-5 Ohm·sm. The plates' diameter was 76 mm, their width - 500 µm. On corresponding batches of plates the layers of Al, Al-Cu (2%) Al-Cu (2%) –Si (1%) 0,8 µm thick were pulverized. Immediately before the sedimentation the plates were polished in the solution of HF (concentrated) for 30 seconds, after the etching they were washed in a hot and the in a cold distilled water, in alcohol and dried up in the thermostat. After that the plates were put into the camera of the vacuum pulverization device. The interval between the processings and loadings of the camera was 30 minutes. After the formation of the adjusted topology of metallization, the plates were exposed to nitrogen burning with the temperature of 450ºС during 15 minutes and the protective coat of SiO2 of 0,9 µm thick was applied. It was followed by the oxide removal from the excretive grounds and the splitting into separate crystals was completed. The quality test of instrument structures was held by means of measuring of contact resistance of contact systems. The amount of resistivity ρ for contacts Al-Cu-Si was (0,76-1.52) 10-6 Ohm·sm2. Results. The analysis of the stability of contact systems before electro-migration demonstrated, that the Al-Cu-Si systems did not prove any refusal either in the process of exposure to the temperature of 150ºС, or in the course of electro-migration tests, whereas for the structures Al and Al-Cu a significant quantity of refuses was observed. Thus, after 1000 hours of exposure to the temperature of 150ºС 2 of 15 Al structures and 2 of 15 Al-Cu structures demonstrated refuses. As a result of electro-migration tests during 256 hours with the temperature of 215о С there were 14 refusals (with 20 tested structures) for Al and 7 refusals for Al-Cu. In the course of the analysis of Al-Cu-Si structures neither in the process of exposure to the temperature of 150ºС, nor in the course of electro-migration tests, there were no refusals observed, only insignificant amount of silicon precipitate was noticed. For Al and Al-Cu structures a significant amount of refusals and silicon erosion are characteristic. Originality. The variation of the contact resistance points out the necessity of thorough preparation of contact windows before the contact. It was also proved, that cleaning of the backings surface in the processing camera of the vacuum device immediately before the metal coating significantly diminishes the variation of the contact resistance. Practical value. All in all, it is advisable to apply Al-Cu-Si contact systems for a series of photoelectric appliances. Technological processes of the systems obtained do not demand any complicated equipment, the applying of precious metals and require a small amount of operations. The optimal width of the layers in the contact system recommended was approximately 500 0 А.
Authors and Affiliations
S. Ivanchikov, Z. Nikonova, О. Nyebesnyuk, A. Nikonova
Keywords
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