Local aluminum–silicon contacts by layer selective laser ablation

We demonstrate damage free selective laser ablation of silicon nitride from a silicon nitride/amorphous silicon double layer. This approach allows local contact formation to passivated silicon. Thereby the remaining amorphous silicon dissolves in evaporated aluminum by annealing. This technique is especially useful for contacting thin emitters since it avoids any damage to the silicon substrate. We demonstrate a local contact resistivity of 0.8±0.3 mΩ cm2 on a phosphorous diffused emitter with a peak doping density of 2×1020 cm−3. Laser treated as well as non-treated areas show the same carrier lifetime of 2000 μs on 100 Ω cm mono-crystalline silicon, proving the selective ablation.