Hi Javaneh

You Can obtain ohmic contacts by creating surdoped zone near the interfaces Al/Si. The carriers will ne transported by tunneling.

As above - yes you can, provided the n- and p-layers are sufficiently highly doped. The optimum annealing temperature depends on the details of your passivation layer, and I'd recommend testing it yourself for your layers. It will probably be in the range 300-450C.

Adding to the respected colleges above low resistance ohmic contacts are produced by firstly making high low junction such as p+-p or n+-n and then depositing aluminum on it . In this way the formed Metal silicon contact will be a tunnel junction provided the doping of the heavily doped layer under metal must be greater than the effective density of state to affect a nondegenerate semiconductor. If the doping is smaller then a nonohmic contact may be formed. I studied this effect and you can refer to the following link to get the paper:https://www.researchgate.net/publication/232710923_A_Zekry_and_G_El-Dllal_effect_of_MS_contact_on_the_electrical_behavior_of_solar_cells_Journal_of_solid-state_Electronics_Vol31_No1_1988

The other method to produce an ohmic M-S contact by making the recombination rate at the interference of the MS contact  very large.

Best wishes

Article A. Zekry and G. El-Dllal, “ effect of MS contact on the elec...