Transverse electric and transverse magnetic polarization active intersubband transitions in narrow InGaAs quantum wells

Polarization-resolved infrared spectroscopy has been used to demonstrate the existence of transverse electric (TE) and transverse magnetic (TM) active intersubband transitions in lattice-matched, unstrained In0.53Ga0.47As/In0.52Al0.48As and strained In0.7Ga0.3As/AlAs quantum wells grown by molecular beam epitaxy on Fe-doped semi-insulating InP (001) substrates. It is shown that a previously reported intersubband absorption peak at 0.3 eV in a 4.0-nm wide, lattice-matched InGaAs/InAlAs quantum well can be resolved into two peaks active for TE and TM polarizations, respectively, with a 10 meV splitting between them. Bound to quasibound state transition at 0.59 eV (2.1 μm) for a narrow, 2.8-nm-wide InGaAs quantum well has also been observed. Group symmetry analyses considering D2d symmetry, tetragonal perturbation of local crystal and strain deformation potential, and interface roughness of the ternary quantum-well structure is proposed to explain the polarization selection rules, and the Stark splitting in the intersubband absorption.