Refractive index changes in AlGaN/GaN heterostructure field-effect transistors

Using the envelope wavefunction approximation and the compact density matrix formalism, we have investigated theoretically the linear and nonlinear refractive index changes in AlGaN/GaN quantum well heterostructures aimed for designing electro-optical modulators. The confining potential in the heterostructures is assumed to be semiparabolic. Simulated results reveal that the refractive index changes strongly depend on both the Al composition and the delta-doping concentration. On the other hand an applied electric field further enhances the refractive index changes. Compared with AlGaAs/GaAs heterostructures and quantum dots, the amount of the refractive index is larger in the AlGaN/GaN quantum well heterostructures studied. The fact to have a large refractive index change leads to the use of relatively weaker incident beam intensities.