Modifying PC1D to model spontaneous & piezoelectric polarization in III-V nitride solar cells

The III-nitrides offer substantial potential to develop ultra-high efficiency solar cells due to their direct-band gap ranging from 0.65eV (InN) to 6.2eV (AlN). Spontaneous and piezoelectric polarization present in the wurtzite group III-nitrides (AlN, GaN, InN and their alloys) influence the optical and electrical properties of these materials and thus, have significant device design consequences for solar cells. However, existing semiconductor modeling programs, particularly those targeting solar cells, do not include the effects of polarization, giving rise to inaccurate design rules and efficiency expectations for III-nitride solar cells.; The widely used semiconductor simulation program PC1D is identified to incorporate polarization into it for extensively studying the effects of polarization on the optoelectronic properties of a solar cell. We study the working of PC1D and the different discretization methods used for the purpose of solving the non-linear basic semiconductor equations. We present a description of the theory of polarization as applied to solar cells which calculates strain and relaxation in epitaxial layers arising due to lattice and thermal-expansion mismatch with the substrate. The gradients in net polarization at surfaces and heterointerfaces enable formation of 2-dimensional electron or hole gases.; Modifications made to PC1D to implement the model for polarization for the III-nitride material system are explained. Issues governing the modifications are dealt with and the problem of non-convergence due to the addition of polarization induced charge is observed and traced in the code. The modified program is currently being used at the Solar Power Program at the University of Delaware to simulate and compare results with fabricated high-band gap GaN/InGaN solar cells, and identify loss mechanisms and realistic efficiency goals.