Stress management: New model describes heterostructure’s piezoelectric responses to external pressure

Because of their wide bandgap, stable chemistry and high melting point, aluminum gallium nitride/gallium nitride (AlGaN/GaN) heterostructure wafers used in power and photoelectronic devices have shown potential to work under extreme temperatures and radiation exposure. Pressure and external stress affect the material’s polarization field and the density of its electrons in taking the form of a two-dimensional electron gas (2DEG), making the heterostructures promising pressure sensor materials. Researchers are now starting to make inroads in understanding the heterostructures’ ability to manage stress.

A team of researchers demonstrated a fully coupled 3-D electro-mechanical model that can simulate how induced strains and 2DEG density in AlGaN/GaN heterostructures are affected by features of processing the material. Publishing its results in AIP Advances, the group found that edges caused by processing have significant influence on the 2DEG density for highly strained AlGaN/GaN wafers with bending.

The team constructed its model from data obtained by bending AlGaN/GaN high electron mobility transistors (HEMTs), including changes in the Schottky energy barrier height, channel resistance and conductance, and the transport characteristics. They then used simulations to investigate the roles of the mesa used for isolation, the ohmic contact metal, the gate and the passivation.

The results show that factors such as distance between the edges, depth of the edges, and direction the uniaxial stress is exerted have significant influence on the induced strains and the 2DEG density. The paper asserts that these changes can be explained by the fact that the edges can alter the stress distribution in the heterostructure, further altering 2DEG density via the piezoelectric effect.

Next, the group will leverage the previous findings in hopes of fabricating high-performance AlGaN/GaN-based devices in the near future.

Source: “Modification of strain and 2DEG density induced by wafer bending of AlGaN/GaN heterostructure: Influence of edges caused by processing,” by Ashu Wang, Lingyan Zeng, Wen Wang, and Fernando Calle, AIP Advances (2018). The article can be accessed at https://doi.org/10.1063/1.5020149 .