Spontaneous polarization effects in wurtzite GaN/AlGaN quantum wells and comparison with experiment

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Abstract
Electronic and optical properties of wurtzite GaN/AlGaN quantum well(QW) structures with the spontaneous (SP) and piezoelectric (PZ) polarizations are investigated. Although the PZ field in the well is zero where there is no strain if the QW structures are grown on a thick GaN layer, there may still exist a strong field in the well due to the difference between the SP polarizations in the well and barrier regions. It is shown that the transition energies have significant dependence on both the well and the barrier widths and the many-body optical gain is reduced largely due to the SP polarization. In particular, in the case of a QW structure with a large well width, the reduction of the optical gain is dominant due to larger spatial separation between the electron and hole wave functions. These results suggest that a QW structure with a thin well width below 30 Å is desirable for QW lasers. We show that the theoretical transition energies agree very well with the experimental results for several Al compositions and barrier widths. The estimated SP polarization constant for AlN is about −0.040 C/m 2 , which is smaller than the value (−0.081 C/m 2 ) predicted by previous theory.
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