Effects of impurity-free and impurity-induced disordering on the optical properties of GaAs/(Al,Ga)As distributed Bragg reflectors

The variation of the reflectivity and stopband width of disordered GaAs/(Al,Ga)As distributed Bragg reflectors (DBRs) is studied by thermal annealing of semiconductor DBRs and modeled by simulating interdiffusion of Al and Ga at the interfaces within the DBR. Undoped mirrors show stability in their reflectivity and stopband width for annealing durations of up to 24 h. Heavily Si-doped mirrors show strong degradation for annealing durations as short as 1 h. Using the model, excellent agreement with experimental results is found and interdiffusion coefficients can be estimated. The results show that important optical parameters are unchanged for short diffusion lengths, but drastically degrade for larger diffusion lengths. The results indicate the limits of thermal processing for device structures containing GaAs/(Al,Ga)As DBRs. The ability to accurately predict the effects of disordering on DBRs permits the proper design of vertical cavity structures containing DBRs, by specifically accounting for the effects of disordering.