LEVEL ANTICROSSING AND RELATED GIANT OPTICAL ANISOTROPY CAUSED BY THE STARK-EFFECT IN A STRAINED (110) QUANTUM-WELL

The effects of an electric field along the [110] growth axis on the polarization properties of the interband transitions in a (110) quantum well are studied within a multiband effective-mass approximation. The transfer-matrix method is applied to coupled effective-mass equations in order to obtain the eigenenergies and eigenstates of holes under an electric field within a steplike approximation to the potential. The calculated results are shown for a GaxIn1-xAs/AlyIn1-yAs quantum well grown on a (110) InP substrate in which the GaxIn1-xAs well layer is strained due to a lattice mismatch to the substrate, while the lattice constant of the AlyIn1-yAs barrier layer is matched to that of the substrate. In the absence of an electric field, the first hole level (nu1) in a quantum well having a Ga content of x = 0. 58 and a well width of 80 angstrom is proved to have a light-hole character, while the second level (nu2) has a heavy-hole character, due to the effect of tensile strain. The calculated result of the electric-field dependence of the hole energy levels for this quantum well shows an anticrossing behavior between the nu1 and nu2 levels. The optical matrix element of the dipole transition between the first electron state (c1) and the nu1 or nu2 state shows an anomalous behavior in the electric-field dependence, related to the anticrossing: For linear polarization along the [110] growth axis, the optical matrix element for the c1-nu1 transition suddenly decreases with increasing field, while that for the c1-nu2 transition rises in the anticrossing region, representing character changes from light- to heavy-hole-like and vice versa; for polarization parallel to the (110) quantum well, the in-plane optical anisotropy is extremely enhanced to as much as 100% near the anticrossing.