We report results from detailed optical spectroscopy from MOCVD grown GaN/AlGaN multiple QWs and superlattices, as opposed to most previous studies where MBE was employed. The wurtzite group III nitrides are tetrahedrally coordinated direct band gap semiconductors having a hexagonal Bravais lattice with four atoms per unit cell. As a consequence of the noncentrosymmetry of the wurzite structure and the large ionicity factor of the covalent metal–Nitrogen bond, a large spontaneous polarization oriented along the hexzgonal c- axis is predicted. In addition, GaN is highly piezoelectric[1]. These macroscopic polarizations play an important role in nitride based QW by producing large build-in electric fields along c-axis.

In this paper we will present theoretical and experimental results demonstrating how polarization induced electric fields and bound interface charges in GaN/AlGaN MQWs affect the emission peak energy, PL line shape as well as the emission line width. We have calculated the approximate value of spontaneous and piezoelectric and depletion field in these structures. Our results demonstrate that both of polarization fields and depletion fields need to be considered in the interpretation of the experimental data. The theoretically estimated fields in this work are consistent with the experimental data. The transition energy of the heavy hole and electron ground state, E_e-hh, in GaN/AlGaN MQWs were measured using triangular well profile approximation [2]. The theoretically calculated transition energy have been compared to experimental energy position and it is found to be in good agreement with the data.

[1] H. Morkoc; Nitride Semiconductors and Devises; ed. By R. Hull, R. M. Osgood, Jr. H. Sakaki and A. Zunger; Springer-Verlage, (1999).

[2] R. Cingolani, A. Botcharev, H. Tang, H. Markoc, G. Traetta, G. Coli, M. Lomascolo, A. Di Carlo, F. Della Sala, and P. Lugli; Phys. Rev. B 61, 2711 (2000).

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