Two dimensional electron gas in GaN heterojunction field effect transistors structures with AlN spacer

Qian Fan; Jacob H. Leach; Jinqiao Xie; Umit Ozgur; Hadis Morkoç; L. Zhou; D. J. Smith

doi:10.1117/12.811678

19 February 2009 Two dimensional electron gas in GaN heterojunction field effect transistors structures with AlN spacer

Qian Fan, Jacob H. Leach, Jinqiao Xie, Umit Ozgur, Hadis Morkoç, L. Zhou, D. J. Smith

Proceedings Volume 7216, Gallium Nitride Materials and Devices IV; 72162N (2009) https://doi.org/10.1117/12.811678
Event: SPIE OPTO: Integrated Optoelectronic Devices, 2009, San Jose, California, United States

Abstract

Near lattice matched Al_0.81In_0.19N/GaN heterojunction structures are compared with conventional Al_0.3Ga_0.7N/GaN heterojunctions in terms of the sheet density and mobility and their dependence on barrier and spacer layer parameters. With the insertion of an AlN spacer, the mobility of both structures is improved dramatically. Self-consistent solution of Poisson-Schrödinger equations was developed in order to determine the band structure and carrier distribution in these GaN based heterostructures in an effort to gain insight into the experimental observations. Surface donor states were included to account for the origin of electrons in 2DEG, which is treated as charge neutralization conditions in the simulation. Also the change in the piezoelectric polarization due to the electromechanical coupling effect, and shift of band gap caused by uniaxial strain were both included in the calculations. The calculated sheet density is close to the measured values, especially for the AlGaN samples investigated, but a notable difference was noted in the AlInN cases. The discrepancy is confirmed to be caused by the existence of a Ga-rich layer on the top of AlN spacer during the growth interruption, which can split the 2DEG into two channels with different mobilities and lower the overall sheet density. When the modifications made necessary by this GaN layer are taken into account in our model for the AlInN barrier case, the calculations match with the experimental data. When the spacer thickness increase from 0.3 to 3 nm, the total sheet density was found to slightly increase experimentally, which agreed with the theoretical prediction.

Citation Download Citation

Qian Fan, Jacob H. Leach, Jinqiao Xie, Umit Ozgur, Hadis Morkoç, L. Zhou, and D. J. Smith "Two dimensional electron gas in GaN heterojunction field effect transistors structures with AlN spacer", Proc. SPIE 7216, Gallium Nitride Materials and Devices IV, 72162N (19 February 2009); https://doi.org/10.1117/12.811678

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KEYWORDS

Aluminum nitride

Gallium nitride

Heterojunctions

Polarization

Field effect transistors

Data modeling

Metals

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