How to establish the correlation between EpiEL test and device results
This application note will briefly explain how EpiEL system establishes the correlation between EpiEL test and various device results.
For a given LED material, there are many kinds of possible devices in the world
by different processes and manufacturers; however the EpiEL test will only give
out one kind of test result with a given kind of probe. Furthermore, even though
the instant device formation of EpiEL reveals Vf very close to the Vf of real
fabricated device, there is still some difference between EpiEL device formation
and a real LED device fabrication. Usually EpiEL test exhibits a slightly higher
Vf compared with the Vf of corresponding fabricated device due to its relatively
higher internal resistance.
In order to eliminate this difference and to correlate one EpiEL test with different
fabricated devices, the new generation of MaxMile EpiEL technology introduces a
simulation factor in EpiEL test profile to extract the estimated device LIV associated
to a specific device fabrication. As shown in following LIV curves, the measured IV
curve is in yellow and estimated device LIV curves are in blue. At a given current,
due to relatively high internal resistance, the EpiEL measured Vf exhibited a slightly
higher Vf than the Vf of real device; after using the above simulation factor, the
estimated device LIV is very similar to that of a real device. By using different
simulation factors, the influence of EpiEL probe itself will be eliminated, and all
kinds of device LIV can be closely simulated and extracted; correspondingly the extracted
device LIV gives out much better test performance.
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