title: Effects of Thickness of a Low-Temperature Buffer and Impurity Incorporation on the Characteristics of Nitrogen-polar GaN.
abstract: In this study, effects of the thickness of a low temperature (LT) buffer and impurity incorporation on the characteristics of Nitrogen (N)-polar GaN are investigated. By using either a nitridation or thermal annealing step before the deposition of a LT buffer, three N-polar GaN samples with different thicknesses of LT buffer and different impurity incorporations are prepared. It is found that the sample with the thinnest LT buffer and a nitridation step proves to be the best in terms of a fewer impurity incorporations, strong PL intensity, fast mobility, small biaxial strain, and smooth surface. As the temperature increases at ~10 K, the apparent donor-acceptor-pair band is responsible for the decreasing integral intensity of the band-to-band emission peak. In addition, the thermal annealing of the sapphire substrates may cause more impurity incorporation around the HT-GaN/LT-GaN/sapphire interfacial regions, which in turn may result in a lower carrier mobility, larger biaxial strain, larger bandgap shift, and stronger yellow luminescence. By using a nitridation step, both a thinner LT buffer and less impurity incorporation are beneficial to obtaining a high quality N-polar GaN.
authors.affiliation: Department of Electronic Engineering, Southern Taiwan University of Science and Technology, Tainan, Taiwan, R.O.C.
authors.forename: Fann-Wei
authors.initials: FW
authors.lastname: Yang
authors.affiliation: Department of Applied Physics, National University of Kaohsiung, No.700, Kaohsiung University Rd., Nan Tzu Dist., 81148, Kaohsiung, Taiwan, R.O.C.
authors.forename: Yu-Yu
authors.initials: YY
authors.lastname: Chen
authors.affiliation: Department of Applied Physics, National University of Kaohsiung, No.700, Kaohsiung University Rd., Nan Tzu Dist., 81148, Kaohsiung, Taiwan, R.O.C.. swfeng@nuk.edu.tw.
authors.forename: Shih-Wei
authors.identifier: http://orcid.org/0000-0002-6548-7468
authors.initials: SW
authors.lastname: Feng
authors.affiliation: Key Laboratory of Nanodevices and Applications, Suzhou Institute of Nano-tech and Nano-bionics, Chinese Academy of Sciences, Suzhou, China.
authors.forename: Qian
authors.initials: Q
authors.lastname: Sun
authors.affiliation: Department of Electrical Engineering, Yale University, New Haven, CT, USA.
authors.forename: Jung
authors.initials: J
authors.lastname: Han
keywords: Biaxial strain; Buffer layer; Impurity incorporation; N-polar GaN; Thickness