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

Electronic and optical properties of wurtzite GaN/AlGaN quantum well (QW) s tructures with the spontaneous (SP) and piezoelectric (PZ) polarizations ar e 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 stil l exist a strong field in the well due to the difference between the SP pol arizations in the well and barrier regions. It is shown that the transition energies have significant dependence on both the well and the barrier widt hs and the many-body optical gain is reduced largely due to the SP polariza tion. 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 separa tion between the electron and hole wave functions. These results suggest th at a QW structure with a thin well width below 30 Angstrom is desirable for QW lasers. We show that the theoretical transition energies agree very wel l with the experimental results for several Al compositions and barrier wid ths. 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 theo ry. (C) 2000 American Institute of Physics. [S0003-6951(00)01915-X].