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Molecular Beam Epitaxy Growth and Characterization of Germanium‐Doped Cubic Al x Ga 1− x N
Author(s) -
Deppe Michael,
Henksmeier Tobias,
Gerlach Jürgen W.,
Reuter Dirk,
As Donat J.
Publication year - 2020
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.201900532
Subject(s) - doping , molecular beam epitaxy , germanium , analytical chemistry (journal) , materials science , photoluminescence , epitaxy , ternary operation , band gap , crystallography , mole fraction , silicon , chemistry , nanotechnology , optoelectronics , chromatography , computer science , programming language , layer (electronics)
In cubic (c‐)GaN Ge has emerged as a promising alternative to Si for n‐type doping, offering the advantage of slightly improved electrical properties. Herein, a study on Ge doping of the ternary alloy c‐Al x Ga 1− x N is presented. Ge‐doped c‐Al x Ga 1− x N layers are grown by plasma‐assisted molecular beam epitaxy. In two sample series, both the Al mole fraction x and the doping level are varied. The incorporation of Ge is verified by time‐of‐flight secondary ion mass spectrometry. Ge incorporation and donor concentrations rise exponentially with increasing Ge cell temperature. A maximum donor concentration of 1.4 × 10 20 cm −3 is achieved. While the incorporation of Ge is almost independent of x , incorporation of O, which acts as an unintentional donor, increases for higher x . Dislocation densities start increasing when doping levels of around 3 × 10 19 cm −3 are exceeded. Also photoluminescence intensities begin to drop at these high doping levels. Optical emission of layers with x > 0.25 is found to originate from a defect level 0.9 eV below the indirect bandgap, which is not related to Ge. In the investigated range 0 ≤ x ≤ 0.6, Ge is a suitable donor in c‐Al x Ga 1− x N up to the low 10 19 cm −3 range.