Influence of composition pulling effect on the two-dimensional electron gas formed at Al y In x Ga 1-x-yNGaN interface

Abstract

The piezoelectric field generated at the Aly Inx Ga1-x-y NGaN interface creates a two-dimensional electron gas (2DEG). The maximum 2DEG mobility in Aly Inx Ga1-x-y NGaN, for a nominal composition of x=0.01 and y=0.07, is obtained for the 40-nm -thick quaternary epilayer. With further increase in the Aly Inx Ga1-x-y N thickness, the mobility drops due to the generation of V defects and misfit dislocations. The 2DEG carrier concentration increases with the thickness due to the composition pulling effect observed during growth where the Al content increases toward the surface. This effect coupled with the stronger piezoelectric field results in a significant band bending and a deeper potential well is created for the sample with a thicker AlInGaN epilayer. The integrated intensity ratio of the photoluminiscence emission from the 2DEG and the AlInGaN band-edge emission, I2DEG IBE, is studied as a function of temperature for AlInGaN epilayers of different thickness. The effect of strain relaxation and V-pit formation on the 2DEG confinement in AlInGaNGaN is also discussed. © 2005 American Institute of Physics.