Study of wurtzite and zincblende GaN/InN based solar cells alloys: first-principles investigation within the improved modified Becke-Johnson potential

Abstract

Wurtzite GaInN alloys with flexible energy gaps are pronounced for their potential applications in optoelectronics and solar cell technology. Recently the unwanted built-in fields caused by spontaneous polarization and piezoelectric effects in wurtzite (WZ) Ga1-xInxN, has turned the focus towards zinc-blende (ZB) GaInN alloys. To comprehend merits and demerits of GaInN alloys in WZ and ZB structures, we performed a comparative study of the structural, electronic and optical properties of Ga1-xInxN alloys with different In concentration using first-principles methodology with density function theory with generalized gradient approximations (GGA) and modified Becke Johnson (mBJ) potential. Investigations pertaining to total energy of Ga1-xInxN for the both phases, demonstrate a marginal difference, reflecting nearly equivalent stability of the ZB Ga1-xInxN to WZ-Ga1-xInxN. The larger ionic radii of indium (In), result in larger values of lattice parameters of Ga1-xInxN with higher In concentration. For In deficient Ga1-xInxN ,In. N, at first, the formation enthalpies increase rapidly as the In content approaches to 45% in WZ and 47% in ZB, and then decreases with the further increase in In concentration. ZB-Ga1-xInxN alloys exhibit comparatively narrower energy gaps than WZ, and get smaller with increase in In contents. The smaller values of effective masses of free carriers, in WZ phase, than ZB phase, reflect higher carrier mobility and electrical conductivity of WZ-Ga1-xInxN. Moreover wide energy gap of WZ-Ga1-xInxN results in large values of the absorption coefficients comparatively and smaller static refractive indices compared to ZB-Ga1-xInxN. Comparable electronic and optical characteristics of the ZB-Ga1-xInxN to WZ-Ga1-xInxN endorses it a material of choice for optoelectronics and solar cell applications besides the WZ Ga1-xInxN (C).