LINEAR AND NONLINEAR INTERSUBBAND OPTICAL PROPERTIES IN A STEP QUANTUM WELL WITH AN APPLIED ELECTRIC FIELD

Within the framework of the effective-mass envelope-function theory , the field-dependent intersubband optical properties of a Al_0.4Ga_0.6As/Al_0.2Ga_0.8As/GaAs step quantum well are investigated theoretic ally based on the periodic boundary condition. A very large Stark shift occurs when the lowest subband electron remains confined to the small well while the hig her subband electron confined to the big well. The optical nonlinearity in a step well due to resonant intersubband transition(ISBT) is analyzed using a density matrix approach. The second-harmonic generation coefficient \chi⁽²⁾_2\omega and nonlinear optical rectification \chi⁽²⁾₀ have also been investigated theoretically. The results show that the ISBT in a step well can generate very large second order optical nonlinearities, \chi⁽²⁾₀ and \chi⁽²⁾_2\omega can be tuned by the electric field over a wide range.