Non-Equilibrium Defect Formation Energies—What Happens to Defect Concentrations in the Presence of Excess Carriers?

High energy ions produce point defects athermally via displacements, but should the numbers of point defects be modified during processing or device service because of non-equilibrium carrier densities? For example, what should be the steady state numbers of point defects in a radiation detector crystal of CdTe grown using optical heating, or that same crystal under bias operating as a detector, or in a CdTe solar cell under exposure to light? The conventional thermodynamics of equilibrium point defect numbers has no answers for these non-equilibrium but steady-state situations. Multiple theories have been proposed in the past that can all be shown to a-priori assume an effecitve formation energy that is some function of quasi-Fermi levels. We have recently developed an entirely new framework starting from indisputable touchstones of semicondcutor and defect physics and instead deriving the form of the defect formation energies. Non-equilibrium carrier densities exist in semicondcutor processing, whether by accident or design, and especially under extreme operating conditions. A correct theory of how depletion, photogenertion, and injection affect the thermodynamic driving forces for defect creation and annihilation is long overdue and will enable prediction and understanding.