N.V. Vishnyakov – Ph.D.(Eng.), Associate Professor, 

Department «Micro- and nanoelectronics», Ryazan State Radio Engineering University named after V.F. Utkin E-mail: rcpm-rgrtu@yandex.ru; rcpm@rsreu.ru

The effect of lowering the effective height of the potential barrier at the metal – amorphous hydrogenated silicon contact is considered. This contact can act as a locking barrier or ohmic contact in thin-film electronics elements on disordered semiconductors. The height of the potential barrier and contact phenomena are significantly influenced by donor-like localized states located near the Fermi level in the band gap of an amorphous semiconductor. This effect is manifested by the action of image forces (Schottky effect) and an increase in the tunnel transparency of the barrier (tunnel effect), which lead to a decrease in the effective height of the barrier under applied reverse bias voltage. The high density of electrically active localized states in amorphous hydrogenated silicon (gF0≥1016cm−3eV−1) influences the distribution of the electric potential along the coordinate on the metal - amorphous semiconductor contact and leads to the formation of a tunnel-transparent near-contact region. According to the calculation performed in the work, at gF0=1019cm−3eV−1 and an external reverse voltage of 2 V, the decrease in the effective barrier height due to tunneling is about 0,35 eV. Lowering the height of the barrier due to the action of image forces also takes place, but it is «masked» by the tunnel effect. For similar conditions, this decrease is about 0,16 eV.

A comparative calculation was carried out for the case of metal contact with strongly doped crystalline silicon, which showed significant differences in the results of the tunnel effect and the Schottky effect in the case of metal contact with crystalline and amorphous hydrogenated silicon. For the metal-crystalline silicon barrier, the Schottky effect has a more notable effect on lowering the effective barrier height than the tunnel effect under selected boundary conditions in contrast to the metal - amorphous silicon barrier. It should be noted that the calculations did not take into account the effect of surface states in silicon at the interface with the metal. The ideas presented in the paper allowed us to propose new ways of forming tunnel quasi ohmic contacts in thin-film structures based on unalloyed or weakly alloyed amorphous hydrogenated silicon by creating a tunnel-transparent near-surface layer. The relevance of this work is providing a detailed understanding of the nature of the metal – amorphous semiconductor contact to increase the efficiency of thin-film electronics devices based on disordered semiconductor materials.

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19. Pat. RF na izobretenie № 2392688 ot 20.06.2010 g. Sposob sozdaniya omicheskikh kontaktov v tonkoplenochnykh ustroistvakh na amorfnykh nelegirovannykh poluprovodnikakh. Avachev A.P., Vikhrov S.P., Vishnyakov N.V., Mitrofanov K.V., Mishustin V.G., Popov A.A.  (Zayavka № 2009118861 ot 20.05.2009 g.). (in Russian)