Deep-Level Transient Spectroscopy System
The standard and still most sensitiv DLTS mode. A Schottky diode or a p/n junction capacitance is used to fill trap levels and detect the emission of electrons or holes out of the trap level into the conduction or valance band. The emission process follows an exponential time law dC = A*exp(tau/t). The amplitude A is directly proportional to the trap concentration, the time constant tau = C*exp(dE/kT), measured as function of the temperature, gives the energy level of the trap in the band gap and the capture cross section.
CC-DLTS (Constant Capacitance-DLTS)
For CC-DLTS a fast regulation amplifier is needed (option for FT 1030). This amplifier regulates the reverse bias voltage during the trap emission process (transient) and during the temperature scan. In effect the information depth will be kept constant during the complete measurement. This is quite important for highly concentrated trap levels (NT ≈ NS) to avoid systematical errors appearing in C-DLTS concerning the concentration calculation. In principle CC-DLTS is not as sensitiv as C-DLTS.
The emission process of electrons or holes into the conduction or valance band can also be observed by detecting the reverse bias current of a diode, FET channel or a resistor structure on a semiconductor material. The traps can either be filled analog to C-DLTS using an electrical puls or using an optical puls (resistor structure mainly). A suitable current amplifier is implemented in the standard FT 1030 system, an optical excitation source optimized for the applicative material can be ordered as an option.
DD-DLTS (Double correlated DLTS)
Is used for getting trap level information out of a definable information depth. C-DLTS is done at 2 different reverse bias conditions and therefore at two different information depths.The difference in C-signal is correlated to the difference in information depth. DD-DLTS can be used for measuring trap distribution profiles. No special hardware option is needed for the FT 1030 DLTS system. FT 1030 software supports DD-DLTS measurement and evaluation.
The Zerbst DLTS is a part of our big MOS/MIS software package. Inversion processes of MIS/MOS diodes can be analyzed using single transient measurment at one definable temperature giving the minority carrier lifetime etc., or using temperature dependent measurements for calculation the minority carrier generation center.
O-DLTS (Optically stimulated DLTS)
Compared to C-DLTS, CC-DLTS and I-DLTS the only difference on O-DLTS is the kind of filling the trap levels. Instead of filling the traps with an electrical puls on O-DLTS an optical puls will be used. Normally the energy of the stimulating light is higher than the bandgap energy of the particular semiconductor. O-DLTS can be used with the above given DLTS modes using the particular signals for the transient detection. An optical excitation source optimized for the applicative material can be ordered as an option.
FETs can be directly characterized. A second bias source is included in the hardware and completely supported by the measurement and analyse software. Parameterized I/V curves can be obtained and analysed. C-DLTS at the gate capacitance at different SD votages or I-DLTS in the source drain region at different gate voltages can be measured. This enables the detection of interface states close to the gate oxide and/or the concentration of traps inside the active channel.
Isothermal Transient Spectroscopy
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