Interdiffused AlGaAs-GaAs quantum well for improved electroabsorptive modulation

This is a theoretical study of the effects of two as-grown structural parameters on the modulation properties of Al_xGa _1-xAs-GaAs quantum wells (QWs), which are the Al concentration in barrier and the thickness of the well layer serving as initial conditions before interdiffusion. The results show that, with a larger Al concentration and a wider well width, the range of interdiffusion for an enhanced electroabsorption (EA) change increases with both of these parameters, while insertion loss increases with the former and decreases with the latter. However, the increase in loss is lower than that of the rectangular QW for the same magnitude of absorption change. The range of a tunable absorption-peak wavelength produced by interdiffusion increases with increasing Al concentration and decreases with increasing well width. Moreover, in a moderately interdiffused QW, the required bias reduces for the same level of EA modulation. For the best device operation, interdiffused QWs with the Al concentration between 0.3 and 0.4 and well width between 10 and 12 nm are most suitable for developing a general-purpose electroabsorptive modulator. When applied in high-speed modulators, the EA of a wide and shallow QW active-region structure can be further enhanced by the use of corresponding interdiffusion