Meaning
Characteristic duration required for a captured charge carrier to be thermally released from a localized defect state back into the conduction or valence band of a semiconductor defines the dynamics of slow defect centers. This physical parameter, termed the trap emission time constant, governs the rate of charge recovery in field-effect transistors. It depends on the energy level of the defect and the surrounding lattice temperature.
This parameter ranges from microseconds to hours depending on the nature of the trap. Determining this value is necessary to model the transient recovery behavior of devices after they are subjected to voltage stress.
Thermal Dependency
Exponential scaling with temperature represents the dominant behavior of this release rate due to the thermal activation of carriers. At higher temperatures, the trap emission time constant decreases rapidly, enabling faster recovery from bias stress. This relationship allows researchers to extract the activation energy of the defect by conducting temperature-controlled tests.
Measurement Method
Transient capacitance measurements and deep-level transient spectroscopy are the primary techniques used to determine this parameter. By applying a filling pulse to populate the defects and then monitoring the recovery phase, engineers calculate the trap emission time constant from the exponential decay curve. This process provides a non-destructive method to map the defect spectrum of the device under test.
Device Correlation
Circuit noise and threshold voltage instability correlate directly with the distribution of these carrier release times. When the trap emission time constant matches the period of the operating frequency, the resulting charge exchange causes random telegraph noise or phase jitter. Managing this parameter is essential for optimizing the low-frequency noise performance of analog and radio-frequency integrated circuits.
