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, ideality factor, 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), typically with n>2. Once the dominant mechanism is identified from the ideality factor, a fit for selected 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 measurement bias in the IVT data set.
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.
IVT provides information complementary to DLTS and TAS measurements. DLTS and TAS provide the spectrum of defects, but don’t indicate directly which defects are most responsible for device limitations. IVT measures the conduction mechanism and associated energy of the defect that is limiting the efficiency of devices such as solar cells, light emitting diodes, photodetectors, lasers, and transistors.
IVT includes Current-DLTS (I-DLTS). I-DLTS is very similar to standard DLTS, except current transients are measured rather than capacitance transients. I-DLTS is used for high resistivity semiconductors. I-DLTS also includes optical filling pulse capabilities for photo-induced current transient spectroscopy (PICTS). Double pulse variations are also included to increase the sensitivity.