Dresden 2009 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 11: Focused Session: Semi- and nonpolar group III nitrides I

HL 11.2: Topical Talk

Dienstag, 24. März 2009, 10:00–10:30, HSZ 01

Optical polarization properties of nonpolar-oriented GaN films for polarization-sensitive and narrow-band photo-detectors — •Holger T. Grahn — Paul-Drude-Institut, Berlin

The optical polarization properties of unstrained and strained GaN films with a nonpolar orientation are reviewed. In unstrained A-plane GaN films, the A exciton becomes completely linearly polarized perpendicular to the c axis, while the B and C excitons are only partially polarized. In M-plane or A-plane GaN films under anisotropic in-plane compressive strain, all three interband transitions between the three uppermost valence bands and the conduction band can become completely linearly polarized for sufficiently large strain values. The complete linear polarization can be directly observed in reflection, transmission or photo-reflectance by a polarization-dependent energy gap. This complete linear polarization can be used to realize polarization-sensitive photo-detectors in the ultraviolet spectral range, which do not need a polarization filter in front of the photo-detector. By combining a polarization filter and photo-detector or two photo-detectors from the same material with their c axes oriented perpendicular to each other, a narrow-band photo-detection configuration can be achieved in the ultraviolet spectral range with a band width below 8 nm. Since both realizations are also polarization sensitive, a configuration with four photo-detectors is necessary to achieve narrow-band sensitivity regardless of the polarization state of the incident light. At the same time, the configuration with four photo-detectors allows for the determination of the absolute angle of polarization.