We simulate a type III InAs/GaSb broken gap junction to evaluate its potential as a tunnel junction. The unique properties of broken gap will enhance current transport between the subcells of a multijunction solar cell and reduce the overall series resistance. A drift diffusion simulator has been developed to study the current characteristics of novel heterostructures. The effect all the major recombination mechanisms such as Shockley - Read - Hall, Radiative, and Auger on the current are included. Also, we investigate the effect of degeneracy on the device by considering the effect of band gap narrowing. In our model we also add effects of thermionic emission and band to band tunneling. As solar cells operate at low voltages we have added a model for low field mobility which might be a limiting factor.