Features
Photoluminescence is a method in which a substance is irradiated with
high-energy light. The emission of lower-energy light is then
detected.
Several sample properties can be obtained from the emission spectrum.
Features include:
Excitation of samples with band gaps up to about 3.5 eV
Spatial mapping of the luminescent intensity and emission peak
full-width half maximum (FWHM)
Sample temperatures between 10 K and 470 K
Non-destructive measurement without special pre-treatment
Application Examples
High-sensitivity detection of defects, e.g., point, stacking faults,
contaminants, such as B and P, in crystals such as Si, 4H-SiC, GaAs,
with or without band-edge emission.
Evaluation of photoluminescent materials
Determination of energy levels of forbidden transitions
Principle
In a PL measurement, the sample is irradiated with light that excites
electrons from the ground state to an excited state. When they return to
their ground state, light is emitted.
Information about any impurities and defects can be obtained by
analysing the emission spectrum in detail. Figure 2 shows the principle of PL with some
examples of radiative processes. The yellow arrow indicates emission
from states inside the conduction band and the cyan arrow band-edge
emission. The brown arrow is a non-radiative transition between the
conduction band and an energy level in the middle of the bandgap
originating from, for example, a dopant. The light green arrow describes
a non-radiative transition between the conduction band and a level
associated with an impurity or defect, whereas the purple arrow
indicates a radiative transition to another impurity energy level near
the valence band.
Figure 2. Principle of
photoluminescence.
Data examples
Figure 3. PL spectrum of GaN.
Figure 4. PL mapping of 1080-1180 nm light emitted from a
polycrystalline Si photovoltaic device.
Figure 5. Mapping of PL of all wavelengths across the entire chip of
a Si power MOSFET device showing regions with crystal defects. The
wavelength of the band-edge luminescence is 375-400 nm.
Figure 6. Close-up of
the defect region in 4H-SiC. The wavelength range of the luminescence
(shown by white dots) originating from stacking faults is 410-440
nm.
Figure 7. Region shown by the red square in Figure 6. The wavelength range of the
luminescence (shown by white dots) originating from stacking fault is
410-440 nm.
Annotated PL maps: PDF file. Raw image data (PNG or JPG) available on
request.
PL spectra of selected locations: Excel file
Measurement specifications
Maximum sample dimensions
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\[150 \times 150 \times 30\]
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\(W \times D \times H\) mm
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\[15 \times 15 \times 5\]
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Measurable wavelength range (depends on filters)
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325 nm excitation with CCD detector
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532 nm excitation with InGaAs detector
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\[\mu\text{m}^{\text{2}}\]
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325 nm excitation and \(25\ ℃\)
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\[\mu\text{m}^{\text{2}}\]
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\[\mu\text{m}^{\text{2}}\]
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Magnification (objective lens)
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CCD detector,
\(\mathrm{\Delta}\lambda = 200\) nm
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InGaAs detector,
\(\mathrm{\Delta}\lambda = 100\) nm
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The temperature can be set within approx. 10K～500K
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(sample stage temperature).
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SiC, \(\lambda_{\text{exc}} = 325\)
nm
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GaN, \(\lambda_{\text{exc}} = 325\)
nm
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*When the accumulated time is required, the number of measurement
points may be reduced or difficult to accept.)
Note: Detection depth largely depends on material and excitation
energy.
Items for enquiries
Purpose and scope of the analysis
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Quantity, availability of preliminary samples
Energy (wavelength) range of interest
Structure, shape, layer structure, film thickness, presence of
patterns
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Desired delivery dates of preliminary and final results
Other relevant information
Caution
The laser irradiation can cause damage to the sample due to heating,
even when sample holder is cooled by liquid He.