Electroluminescence Microscopy of Cross-Sectioned AlGaN/GaN High-Electron Mobility Transistors

We report an electroluminescence (EL) microscopy study of operating cross-sectioned AlGaN/GaN high-electron mobility transistors. By examining devices in a cross-sectional view, the distribution and intensity of photons emitted from underneath the optically opaque metal of the gate and drain structures can be studied. The location and the shape of EL bright spots were quantitatively compared with simulated device behavior, revealing a strong correlation between the measured EL intensity and the expected distribution of hot electrons in the channel. Under constant low-power conditions, the bulk of the EL signal migrates from the drain edge of the gate field plate to the drain edge of the source-connected field plate (SCFP) as the drain bias is increased. Hot electrons have been cited as a dominant contributor to device degradation for some devices, so quantifying their location and bias dependence is critical to understanding how this degradation rate might scale with bias and device design. In addition, devices both with and without an SCFP were imaged to quantitatively investigate the influence of the field plate on the EL signal. Finally, a measurement of the spectra of EL signals is used to estimate the temperature of hot electrons in the device.