Thermal Study of a GaN-Based HEMT

Semiconductors have undergone a continual miniaturization process, and heat dissipation has become one of its most challenging problems with respect to applications. Heat is generated when electrons within the device transfer energy to phonons through scattering by the lattice. Since scattering inside the device is not uniform, this process can generate localized hot spots. This work presents experimental and numerical approaches to the understanding of the thermal behavior of gallium-nitride (GaN) high-electron-mobility transistors (HEMTs) under bias conditions.

An experimental technique for electron and lattice temperature extraction was developed from photoluminescence measurements. Using the peak energy value and the form of the high-energy tail of a single photoluminescence spectrum, electron and lattice temperatures can be simultaneously extracted for a given point inside the device. By a two-dimensional sweep of the entire device, it was possible to create spatially resolved maps for electron and lattice temperatures and to observe localization of the hot regions.

Numerical simulations were performed using a hydrodynamic model to analyze heat generation in semiconductor devices. The governing equations were solved using a commercial code TCAD Sentaurus. Two-dimensional electron and lattice temperature fields were calculated for a HEMT, and the formation of a hot spot observed. It was shown that the locations and values of peak temperatures in the hot regions change on varying the rate of heat that is extracted. Under some circumstances the hot spot was seen to split up into two.

The experimental and numerical results showed qualitative order of magnitude agreement between them in terms of electron and lattice temperatures. The hot regions were experimentally observed in areas where they were expected. Simultaneous electron and lattice temperature maps, which have not been reported until now, provide a valuable tool for the study of hot spot formation within devices. If hot spots can be moved by changing operating conditions, it would be possible to decrease temperature peaks in regions where electrical performance is crucial.