Electroluminescence in AlGaN/GaN HEMTs biased at high drain-source voltages has been investigated. The electroluminescence was observed at the drain edge. This is quite different from the case of AlGaAs/GaAs HEMTs in which the electroluminescence was observed at the gate edge. 2D device simulation was performed to investigate the difference in the EL distribution. The results show that high-density surface traps cause the formation of high-field region at the drain edge. Electroluminescence spectroscopy was also performed. A broad spectrum was obtained in a wavelength range of visible to near-infrared light with a polarization in the direction of parallel to the drain current.
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