The optical properties and their relation to the electronic bandstructure in Si-doped GaInN/GaN multiple quantum well structures typical for near UV laser diode devices are investigated in photoluminescence, photoluminescence excitation and photoreflection spectroscopies. A set of four evenly spaced levels N 0 Á Á Á N 3 is identified covering the spectral range from the lowest luminescence band (N 3 ) to the GaN barrier energy (N 0 ). The splitting of N 3 and N 2 appears as a discrete splitting rather than a continuous localization process. The level splitting is well described by a Stark-like ladder defined by the multi interface bandoffset DE FeL z across the piezoelectric GaN/GaInN/GaN structure.
The absorption properties in hetero-polarization GaN/Al x Ga 1Àx N (x ¼ 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.
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