Signal amplification and leakage current suppression in amorphous silicon p-i-n diodes by field profile tailoring

The performance of amorphous silicon p-i-n diodes as radiation detectors in terms of signal amplitude can be greatly improved when there is a built-in signal gain mechanism. We describe an avalanche gain mechanism which is achieved by introducing stacked intrinsic, p-type, and n-type layers into the diode structure. We replaced the intrinsic layer of the conventional p-i-n diode with i₁-p-i₂-n-i₃ multilayers. The i₂ layer (typically 1-3 μm) achieves an electric field > 10⁶ V/cm, while maintaining the p-i interfaces to the metallic contact at electric fields < 7 × 10⁴ V/cm, when the diode is fully depleted. For use in photo-diode applications the whole structure is less than 10 μm thick. Avalanche gains of 10-50 can be obtained when the diode is biased to approx. 500 V. Also, dividing the electrodes to strips of 2 μm width and 20 μm pitch reduced the leakage current up to an order of magnitude, and increased light transmission without creating inactive regions.