Hot-carrier luminescence in sub-quartermicrometer high-speed GaAs MESFET´s

Hot-carrier luminescence in high-speed GaAs MESFET´s with sub-quartermicrometer gate length was investigated at drain voltages high enough to permit breakdown. The spectral distribution of emitted radiation was analyzed in the energy range of 1.4-2.5 eV. GaAs MESFET´s with a gate length of 0.18 μm yielded a prominent peak from the direct recombination across a GaAs bandgap of 1.43 eV. At energies above 1.65 eV, a broad continuous spectra with two peaks and a shoulder were detected. The two peaks coincide with the indirect recombination energies between holes in the Γ valley and electrons in the L or X valley. These peaks, however, were diminished at drain voltages as high as 7.5 V. It is suggested that the luminescence at energies above the bandgap mainly arises from the recombination of hot carriers, and the luminescence resulting from a phonon-assisted conduction to conduction-band transition is superimposed on it. The luminescence from the gate Schottky diode at reversed bias was also examined. There were no peaks from the direct recombination across the bandgap in the spectra. The light emission at the bandgap energy under the FET operation probably originates from the recombination of cold channel electrons and hot holes, which are generated by impact ionization and swept toward the source