Intersubband resonant enhancement of second-harmonic generation in GaN∕AlN quantum wells

This letter reports on the observation of resonant enhancement by intersubband transitions of the second-harmonic generation of ∼1μm radiation in GaN∕AlN quantum wells grown on AlN∕c-sapphire templates. Quantum wells with a nominal well thickness of 10 ML have been investigated in terms of intersubband linear and nonlinear optical properties. A strong increase of the second-harmonic conversion is observed at a pump wavelength of ∼2μm, which is attributed to double-resonance enhancement of the nonlinear susceptibility by intersubband transitions. The second-order susceptibility at resonance is of the order of 114pm∕V, in good agreement with calculations.