Semiconductor based conductive channels are key elements in electronic devices like high-electron-mobility transistors (HEMTs). Wide bandgap semiconductors (Gallium Nitride, Zinc Oxide etc.) are exceptionally suitable for power electronic applications due to high thermal stability, high breakdown electric fields together with high electron mobility. Those polar materials in the form of heterostructures sustain high density two-dimensional electron (2DEG) gas (>1013 cm-3) due to inherent strong polarisation and thus are able to conduct high current densities.
High power applications naturally determine that the electrical excitations will be strong, and thus, high-field electron transport in the channel must be considered. Here hot-electron physics must be considered and the microwave fluctuation spectroscopy of inequilibrium electron gas can be used in this situation. Fluctuations in most cases can give more valuable (or additional) information on high-field electron scattering (kinetics) compared to other (widely employed) techniques like voltage-current, small-signal modulation or optical techniques like pump probe Raman for the conductive 2DEG channels.
The equipment of Fluctuation research laboratory consists of: a) unique microwave (10 GHz, 40 GHz) pulsed (20 ns - 20 μs) hot-electron fluctuation measurement setup on wafer level (microwave probes, probe station) situated in the shielded room (Faraday cage); b) Pulsed fluctuation spectra setup (30 MHz - 2.5 GHz); c) Capacitance-Voltage (LCR meter) and current-voltage (SMU unit) measurement setups (probe station); d) electrical characterisation system (up to 50 GHz) consisting of S-parameters PNA analyser, signal generator, spectrum analyser together with a probe station.
Available techniques are hot-electron fluctuation spectroscopy for the analysis of hot-electron scattering pecularities at electric fields up to 100 kV/cm where hot-phonons effects are clearly resolved in the wideband polar semiconductors and heterostructures (2DEG gas) based on these semiconductors. Characterisation of electron density profile in heterostructures. Characterisation of selfheating effects in details: acoustic phonon selfheating, hot-Lo-phonon selfheating.
For more information, please contact the theme supervisor E. Šermukšnis.