Absorption Spectroscopy and Band Structure in Polarized GaN/AlxGa1 xN Quantum Wells

The absorption properties in hetero-polarization GaN/AlxGa1 xN (x 1⁄4 0:06) quantum well structures are studied in reflection, photoreflection, and photoluminescence excitation spectroscopy and compared with the results of band structure calculations. Above the energy of the main luminescence transitions we observe three distinct absorption thresholds. From Franz-Keldysh oscillations in the absorption spectra we directly derive the value of the acting electric field within the barriers. Upon this field strength we base a calculation of the electronic band structure and interband transition energies. The results suggest that the observed absorption edges are the AlGaN band edge and two quantized levels involving the crystal-field spilt-off hole.