Investigation of the piezoelectric polarization in (In,Ga)N/GaN multiple quantum wells grown by plasma-assisted molecular beam epitaxy

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Abstract
We have studied the structural and optical properties of a series of (In,Ga)/GaN multiple quantum wells with identical thicknesses but varied In content grown by plasma-assisted molecular beam epitaxy. Careful choice of the growth parameters returns samples with smooth and abrupt interfaces. The shift of the photoluminescence transition energy with externally applied biaxial tension was investigated. We observed a redshift for small In contents while a blueshift was detected for higher In contents. This result is in qualitative agreement with self-consistent band profile calculations taking into account both band gap deformation potentials and piezoelectric polarization charges in these structures. However, the reduction of the polarization induced quantum-confined Stark effect is well in excess of that conventionally calculated for this material system. We attribute this observation to a substantial deviation of the piezoelectric polarization constants of strained layers from those calculated for unstrained material. This finding is shown to be in agreement with recent calculations of the piezoelectric polarization charges for biaxially strained (Al,Ga,In)N layers.