Strain-induced polarization in wurtzite III-nitride semipolar layers

This paper presents growth orientation dependence of the piezoelectric polarization of InxGa1-xN and AlyGa1-yN layers lattice matched to GaN. This topic has become relevant with the advent of growing nitride based devices on semipolar planes [A. Chakraborty , Jpn. J. Appl. Phys., Part 2 44, L945 (2005)]. The calculations demonstrate that for strained InxGa1-xN and AlyGa1-yN layers lattice matched to GaN, the piezoelectric polarization becomes zero for nonpolar orientations and also at another point approximate to 45 degrees tilted from the c plane. The zero crossover has only a very small dependence on the In or Al content of the ternary alloy layer. With the addition of spontaneous polarization, the angle at which the total polarization equals zero increases slightly for InxGa1-xN, but the exact value depends on the In content. For AlyGa1-yN mismatched layers the effect of spontaneous polarization becomes important by increasing the crossover point to similar to 70 degrees from c-axis oriented films. These calculations were performed using the most recent and convincing values for the piezoelectric and elasticity constants, and applying Vegard's law to estimate the constants in the ternary InxGa1-xN and AlyGa1-yN layers.