New technological method of forming an ohmic contact to undoped amorphous silicon hydride semiconductors

Full text: The forming of surface ohmic contacts in thin film field transistors memory and solar cells on Schottky-type barrier and others on base amorphous hydrogenase silicon (a-Si:H) is rather laborious and not prime problem, as known. For example, typical ohmic contact layer materials sometimes exhibit diffusion through the amorphous silicon hydride layer resulting in ill-defined or dimensionally irregular contact and semiconductor regions and, in the extreme case, catastrophic degradation of the semiconductor properties of the material. Further, an oxide barrier may form at the interface, which limits electrical conductivity. Finally, in the prior art, in order to achieve ohmic contacts, it was required that a highly doped (n+- layer) film be deposited on the substrate before or after the amorphous silicon hydride deposition in order to reduce barrier formation at the metal-semiconductor interface. The dopant from gas phase contained gas phosphine for making n+- layer, but phosphine are toxic and explosive gas. This specified problem possible to solve entering in technological process of the creation thin-film device on a-Si:H (and other amorphous hydrogenase semiconductors) additional technological operation annealing the films of the amorphous semiconductor at a temperature of about 400 deg C (hydrogen effusion temperature), during 20-30 min, after the films of the semiconductor on substrate, if and when there is no need to forming the n-type layer. After cooling, an amorphous silicon hydride semiconductor layer covered with the masking dielectric layer, then the optical lithography for opening the windows in masking dielectric layer and evaporation metallic electrode are performed. The concerned method is based on the following known fact. The diffusion process (the evaporation) of the hydrogen occurs from surfaces of a-Si:H film at the temperature 350-450 deg. C. As a result this, concentration of the hydrogen a-Si:H surface layer are sharply decreased. This brings about increase of the conditions density, localized in energy gap of the amorphous semiconductor nearby Fermi level g(EF) or with reduction a content of the hydrogen in a-Si:H alloy, the space-charge region with occurs the reduction, and as result the efficient height of metal - a-Si:H barriers deceases. Consequently, the annealing process provides a highly defective un hydrogenated region through which carriers can easily tunnel. This effect is identified as over barrier emission at decrease of the efficient height of the potential barrier between metal and semiconductor on voltage current characteristic. Thus, this method provides for forming stable ohmic contact between, for example, a metal and amorphous silicon hydride which doesn't require a heavily doped N+ layer