Influence of composition pulling effect on the two-dimensional electron gas formed at AlyInxGa1−x−yN∕GaN interface

• Published in: Journal of applied physics 2005-11, Vol.98 (10)
• Main Authors: Soh, C. B., Chua, S. J., Tripathy, S., Chow, S. Y., Chi, D. Z., Liu, W.
• Format: Article
• Language: English
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.2132090

The piezoelectric field generated at the AlyInxGa1−x−yN∕GaN interface creates a two-dimensional electron gas (2DEG). The maximum 2DEG mobility in AlyInxGa1−x−yN∕GaN, 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 AlyInxGa1−x−yN 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 AlInGaN∕GaN is also discussed.