In Operando Micro-Raman 3-D Thermometry with Diffraction-Limit Spatial Resolution for GaN-based (Opto)electronic Devices

Confocal micro-Raman microscopy performed in the transparent spectral region of a semiconductor can, in principle, be used for operando three-dimensional (3D) thermometry with optical diffraction-limit spatial resolution. However, when applied to high-power GaN-based light-emitting diodes (LEDs), the applicability is hindered by the secondary but nevertheless relatively strong electroluminescence in the visible spectral region that can overwhelm the Raman signal. We develop a “split-time-window” scheme that can mimic the continuous wave operation but without the interference of the secondary emission, which allows us to carry out noninvasive 3D temperature profiling and comprehensive thermal analyses of the whole device at any operation current. The technique is applied to an (InxGa1-x)N/GaN LED to extract its 3D temperature distribution when operated at 350 mA with μm-scale resolution when using a 532-nm laser. This technique allows for in-operando monitoring whether hot spots are associated with device failure. If further correlating with HRSTM investigation, one can obtain the structure information of the hot spots in the device and thus help to determine the device failure mechanism. The approach is equally applicable to other devices, such as power electronic devices.