Finite element modelling of nanoscale porosity effect on GaN piezoelectricity

Gallium Nitride has an important role in electronic and optoelectronic applications. III-Ns generally have a wurtzite crystal structure and are piezoelectric. Indeed, polarization effects play an important role in GaN based applications. e.g., polarization mismatch is responsible for creating the conducting 2D electron gas layer in high electron mobility transistors. Recent reports have shown that nanoscale porosity increases the piezoelectric response of GaN1,2. e.g., it was reported that ~40% porous GaN has a 2–3 times higher piezoelectric coefficient than bulk GaN – from 3 pC/N to about 8 pC/N1. This study studied the effect of one type and degree of porosity on the piezoelectric coefficients.

Here, COMSOL Multiphysics (Software for finite element simulation) was used to simulate the piezo-electricity of the porous GaN relying on the Piezoelectricity module, with emphasis on porosity characteristics. In particular, we will present the study of piezoelectricity as a function of pore depth, sample thickness, pore radius, and pore separation. The simulation was carried out using periodic boundary conditions, we simulated a square unit cell and the pore was cylindrical. A constant stress was applied to the structure and the piezoelectric potential was developed as a result. The results show an increase of piezopotential with pore radius, sample thickness and pore depth and a decrease of piezopotential with pore separation.

The results of the study are not exclusive to GaN, but are transferable to general piezoelectric porous materials, especially in cases where piezoelectricity is not hindered by porosity3.

References

1. Y. Calahorraa et. al., Applied Materials Today, 21 (2020) 100858

2. A. Waseem et.al., Semicond. Sci. Technol. 33 (6) (2018)

3. J.I. Roscow et.al., Eur. Phys. J.-Spec. Top. 228 (7) (2019) 1537–1554