Deep-level transient spectroscopy

Deep-level transient spectroscopy (DLTS) is an experimental tool for studying electrically active defects (known as charge carrier traps) in semiconductors.

DLTS investigates defects present in a space charge (depletion) region of a simple electronic device.

After the pulse, when the voltage returns to its steady-state value, the defects start to emit trapped carriers due to the thermal emission process.

This feature together with a technical simplicity of its design made it very popular in research labs and semiconductor material production factories.

In the conventional DLTS method this frequency multiplied by some constant (depending on the hardware used) is called the "rate window".

By setting up different rate windows in subsequent DLTS spectra measurements one obtains different temperatures at which some particular peak appears.

An example when frequency scan is shown to be useful is for studying modern MOS devices with thin and sensitive gate oxides.

Laplace DLTS is an isothermal technique in which the capacitance transients are digitized and averaged at a fixed temperature.

In cases when this assumption is not fulfilled then the constant capacitance DLTS (CCDLTS) method is used for more accurate determination of the trap concentration.

[17] When the defects recharge and their concentration is high then the width of the device space region varies making the analysis of the capacitance transient inaccurate.

For insulating materials it is difficult or impossible to produce a device having a space region for which width could be changed by the external voltage bias and thus the capacitance measurement-based DLTS methods cannot be applied for the defect analysis.