Drift velocity and diffusion coefficients from time-of-flight measurements
This chapter has reviewed the working principles and the main results obtained with the time-of-flight techniques for hot carriers in covalent and compound semiconductors. The ToF technique has emerged as the most direct and reliable experimental technique for investigating both drift velocity and longitudinal diffusion coefficients. Even if limited to drift velocity, the MToF technique offers the possibility to perform measurements at very high electric fields (up to the limit of electrical breakdown) in materials of medium-low resistivity and very small thicknesses (down to the micrometer region), which are of growing interest in both basic and applied research.
Both drift velocity and diffusivity have been systematically analyzed in covalent semiconductors, while data on compound semiconductors are still somewhat scarce, apart from the case of electrons in GaAs.
In the near future some novel results for high-field drift velocity are to be expected by using the MToF technique, in particular, in the areas of ballistic transport and compound semiconductor heterolayers.
KeywordsElectric Field Strength Drift Velocity Current Signal Solid State Electron Current Waveform
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