Evolution of Indium Aluminum Oxide with and Without Tin Doping During Cadmium Telluride Deposition and Processing

Numerical modeling has proven that to yield the best performance for CdTe-based devices it is necessary to have a carrier concentration on the order of 10¹⁶ cm^-3 with lifetimes up to 100s of ns. This highly doped absorber layer constrains the acceptable parameter space for other layers of the device stack, particularly the emitter. To reduce the front recombination and yield high-efficiency devices it is important to achieve proper band alignment with a positive conduction band offset (CBO) between the emitter and absorber interface. Therefore, we introduce the naval two-material system Indium Aluminum Oxide (IAO) as an emitter where the CBO and the bandgap could be tuned and aligned with the absorber by varying the material composition. Sputtered Aluminum was reacted with oxygen to form Aluminum oxide and In₂O₃ was sputtered simultaneously to produce IAO films. AIO films of different bandgaps were fabricated varying the In to Al ratio. Using the AIO emitter with bandgap 4.4 eV we were able to achieve device efficiency of 18%. Along with the CBO alignment, it is important to consider the doping density of the emitter to attain the best performance because it dictates the Fermi level position and the depletion width in the emitter. Carrier concentration of the emitter depends on the oxygen vacancies present which are highly influenced throughout the fabrication process. The introduction of substitutional doping would provide a more controllable method to regulate the carrier concentration in the emitter. Therefore, the studies will be conducted to investigate the evolution of AIO films as a function of Tin doping.