William Angerer - Department of Physics and Astronomy - University ...

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4.3 Photoluminescence of GaN
To characterize the defect structure of GaN we measured the photoluminescence spectra
of several GaN samples. The optical layout for the photoluminescence measurement
is displayed in Fig. 4.10. A 10 mvV 356 nm beam from a Spectra-Physics model
2025-11 CvV Krypton-Ion laser optically excited electrons from the GaN valence band
to the conduction band. The photoluminescent light from the GaN sample was collected
using a lens and then focused on the entrance sli~ of a ISA model HR320 single
pass monochrometer with a 1200 grooves/mm grating. The light was detected with
a Hamamatsu PMT and measured with a lock-in amplifier. The monochrometer slits
were set to 0.25 mm to resolve the spectrum to ",.5 nm. A computer recorded and
analyzed the data and automatically positioned the monochrometer with a stepper
motor. In order to remove the spectral sensitivity of the optical system, we calibrated
the system by recording the spectrum from a lamp with a known power spectrum.
The calibration lamp is a Optronics model 245C, 45 W tungsten-halogen coiled filament
powered by an Optronics model 65DS constant current source. The spectrum
recorded from the tungsten lamp was compared with the known spectral irradiance
of the lamp to determine the spectral response of the photoluminescence system.
The raw data from the GaN photoluminescence spectra was then corrected using the
measured spectral response of the system to yield the real photoluminescence spectra.
vVe measured the photoluminescence at room temperature and at 82 K. The sam-
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