Breaking the Intersubband Selection Rules for Absorption with Zn O Quantum Wells: Light Polarization Sensitivity under Normal Incidence

Abstract

Intersubband (ISB) absorption in quantum wells (QW) at normal incidence is forbidden by the selection rules for light polarization. To be useful under this convenient geometry, QW structures require postgrowth texturing of the surfaces. Here, we demonstrate polarization-sensitive ISB absorption of light at normal incidence using as-grown, nonpolar m-plane ZnO/(Mg,Zn)O multiple QWs without any postprocessing. This breakage of the selection rules is possible due to the formation of a self-assembled V-groove grating QW profile in the direction perpendicular to the c axis, which lies in the growth plane. A geometrical model is developed that predicts the dependence of the ISB absorption strength with the angle of incidence and the QW V-groove angle and is verified by high-resolution transmission electron microscope analysis. As a result of the in-plane anisotropy of the QW grating geometry, a strong light polarization sensitivity is demonstrated under normal incidence, with a predicted polarization sensitivity contrast above 80:1 for a ±5° cone of angles.