Polarization enhanced tunnel junctions in tandem solar cells

By utilizing the spontaneous and piezoelectric polarization inherent in wurtzite III-V nitride semiconductors, the insertion of a strained layer of InGaN, AlN or InN along the [0001] crystal orientation of GaN will result in large sheets of fixed charges. The permanent dipole resulting from these charges contribute directly to the high electric field in these layers that bends the conduction band on the n-side below the valence band of the p-side to enable interband (Zener) tunneling. At low reverse bias, this tunneling current can achieve higher magnitudes than its equally biased forward regime. This is essentially backward conduction, which is useful mechanism in providing a low resistance pathway for current in tandem solar cells.