A Study of Second‐Order Susceptibility in Digital Alloy‐Grown InAs/AlSb Multiple Quantum Wells

Abstract A preliminary measurement of the second‐order nonlinear optical susceptibility of symmetric, coupled, InAs/AlSb multiple quantum well (MQW) structures is acquired through optical second‐harmonic generation (SHG) at fundamental wavelength 1.55 µm. High quality crystalline MQW structures of variable thickness and corresponding bulk AlSb control samples are achieved using a digital alloy epitaxial growth technique that avoids cluster formation and phase segregation. All samples are grown in between a GaSb cap and substrate layer. To isolate SHG from the MQW (or control) layers of interest from cap and substrate contributions, a multilayer optical response matrix model is built and independently tested by accurately reproducing linear reflectivity spectra. While a simplified response matrix analysis of SHG based solely on bulk χ⁽²⁾s does not reproduce the distinct SHG responses of the two sets of samples, the inclusion of an additional interface SHG contribution leads to a successful fit of the data and implies . The results demonstrate a proof‐of‐concept quantification of χ⁽²⁾ in symmetric MQWs and suggest the possibility of engineering χ⁽²⁾ in these structures, particularly with the introduction of well asymmetries.