Role of electric fields in enhancing the doping of semiconductors during epitaxial growth

A novel technique is described to enhance the doping in semiconductors by the application of external electric fields during crystal growth. We show that this technique can enhance the doping efficiency, and suppress self-compensation processes in novel growth techniques such as molecular-beam epitaxy (MBE). An obvious application of this technique is to enhance the doping of wide band gap II–VI semiconductors, where doping in both n- and p-types is usually not possible to achieve because of extensive self-compensation. The physics of the electric field assisted doping process can be described in two parts. First, the external electric field produces a change in the band bending at the growth surface and alters the carrier concentrations near the surface region. This influences doping near the surface region. Second, this enhanced surface doping concentration can be kinetically buried by low temperature growth processes. In our calculations, the dopants are modeled as charged, mobile species that are free to diffuse and drift under electric fields. In the case of MBE growth, we solve for the equilibrium of these species in a moving coordinate frame that travels with the growth front. We have specifically applied our analysis to Li donors in n-type ZnTe. Our results indicate that excellent improvements in the doping concentrations could be obtained under normal MBE growth conditions, with the application of substantial electric fields. We expect that our analysis, and the proposed electric field assisted doping technique will play an important role in the effort to overcome compensation, and achieve selective doping in wide band gap II–VI semiconductors.