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Growth model investigation for AlN/Al(Ga)InN interface growth by plasma-assisted molecular beam epitaxy for high electron mobility transistor applications

: Aidam, R.; Diwo, E.; Godejohann, B.-J.; Kirste, L.; Quay, R.; Ambacher, O.


Physica status solidi. A 211 (2014), Nr.12, S.2854-2860
ISSN: 0031-8965
ISSN: 1862-6300
ISSN: 1521-396X
ISSN: 1862-6319
Fraunhofer IAF ()

Heterostructures with lattice matched Al(Ga)InN barriers have been widely investigated as alternative to standard AlGaN/GaN based high electron mobility transistor structures for high power applications. Mostly these heterostructures comprise a thin AlN based spacer between GaN channel and lattice matched barrier. One key issue for high quality plasma-assisted molecular beam epitaxy (PA-MBE) of these structures is the control of the AlN-Al(Ga)InN interface since optimal growth conditions for high quality AlN differ significantly from those for growth of indium containing material. In this paper, a detailed analysis and a deduced model of the interface growth is presented. The Al/N ratio during AlN spacer growth is likely to influence the subsequent growth of quaternary Al(Ga)InN. Ideal Al/N ratio leads to high performance heterostructures, while slightly Al-rich conditions lead to the formation of Al residues on the substrate surface, which hinder subsequent epitaxial growth. Al/N ratios below unity lead to the deposition of ternary AlGaN instead of binary AlN spacers and to increased alloy scattering. An insertion of a thin GaN layer between spacer and barrier can hinder the formation of Al residues and leads to improved wafer homogeneity.