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Current-Voltage-Temperature (IVT) measurement
is very effective in characterizing the conduction mechanisms in a semiconductor diode, both in forward bias and in reverse
bias. The model that is used to fit the forward bias current is composed of thermionic, recombination, and tunneling components,
and the shunt resistance and series resistance. Analysis of reverse bias currents at fixed voltages reveals the energy of
the dominant generation center. The
different components in forward bias are distinguishable by their ideality factor (n): n=1 for thermionic emission (TE), n=2
for generation/recombination (GR),
and relatively insensitive to temperature for tunneling by field emission or thermionic field emission (FE-TFE). Once the
dominant mechanism is identified from the ideality factor, a fit for all components is performed. The fitting process determines
saturation current values for each of the conduction components, characteristic tunneling energy, the series resistance and
shunt resistance. A semilog plot of the relevant saturation current versus 1/kT (Arrhenius
plot) yields the energies of the barriers involved in each conduction mechanism from the slope. Analysis of the reverse bias
current is straight forward from an Arrhenius plot of the current at each bias. Reverse bias analysis consists of plotting the data in an Arrhenius plot of I/T2
vs 1/kT for each measurement temperature. The change in energy with measurement bias (electric field) provides information
on the potential profile of the rate-limiting step in the generation process. The system manual describes the steps involved in measuring semiconductor transport
characteristics using IVT measurements. The instructions include detailed information on how to load the sample, establish
the initial measurement conditions, acquire the data, and analyze the data. Simulation software is also described. The following figures provide a snapshot of IVT characterization:
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The IVT data is analyzed at each measurement temperature. The forward bias current-voltage curve is fit for the various current
components. Each component's saturation current is saved to a file, along with series resistance and shunt resistance.
In the fitting process, the user selects which components to include in the fitting process.
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After selecting which of the components to include in the fitting process, you select the region of the IV curve to fit. Fitting
an entire data set takes only a few minutes.
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The reverse bias IVT data also contains useful information. An exponential increase in current at fixed voltages indicates
that there is an activated process that sets the reverse bias current. Without any deep level defects in the band gap, the
energy that is calculated is related to the band gap. Otherwise, the generation process can be considered as a two step process,
emission of an electron and a hole. One will be faster than the other, constituting the rate-limiting process.
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The end result is a measure of the energies and conduction mechanisms, providing the characteristics of conduction paths
responsible for device degradation, such as dark current in detectors and solar cells, and non-radiative recombination
paths in LEDs.
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