Optical index of gallium arsenide-aluminum arsenide superlattices in the near infrared

The synthesis of high quality gallium arsenide–aluminum arsenide (GaAs–AlAs) superlattices has initiated a new class of optical materials with important consequences in the area of optoelectronics. For many applications it will be necessary to accurately characterize the optical properties of these materials in frequency regions of interest. In the present investigation, infrared reflectance spectroscopy is used to determine the optical indices of several GaAs–AlAs superlattice films in the near-infrared region (4000–10,000 cm−1). Each of the superlattices under study had an average aluminum mole fraction equal to 0.523. The reflectivity measurements indicate that the optical index of a particular superlattice can be higher or lower than that of the equivalent AlGaAs alloy depending on the layer periodicity of the superlattice. These results are compared with theoretical treatments of GaAs–AlAs superlattices1 and with prior experimental studies at energies above 1.2 eV.2