Effect of the doping and the Al content on the microstructure and morphology of thin Al{sub x}Ga{sub 1{minus}x}N layers grown by MOCVD[Metal Organic Chemical Vapor Deposition]
Al{sub x}Ga{sub 1{minus}x}N {l_brace}x = 30% (doped and undoped), 45% (doped){r_brace} thin films were grown by MOCVD on {approximately} 2 {micro}m thick GaN layer using Al{sub 2}O{sub 3} substrate. These films were designed to be the active parts of HFETs with n{sub s}{mu} product of about 10{sup 16}(Vs){sup {minus}1}. The layers were then studied by means of transmission electron microscopy (TEM) techniques. In this paper, it is shown that the Al{sub x}Ga{sub 1{minus}x}N layer thickness was non-uniform due to the presence of V-shaped defects within the Al{sub x}Ga{sub 1{minus}x}N films. The nucleation of these V-shaped defects has taken place about 20 nm above the Al{sub x}Ga{sub 1{minus}x}N/GaN interface. Many of these V-shaped defects were associated with the presence of the threading dislocations propagating from the GaN/Al{sub 2}O{sub 3} interface. The authors show that the density of these V-shaped defects increases with the doping level and also with the Al mole fraction in the films. The formation mechanism of the V-shaped defects seems to be related to the concentration of dopants or other impurities at the ledges of the growing film. This suggestion is supported by high resolution TEM analysis. The growth front between the V-shaped defects in the lower Al concentration thin films was planar as compared with the three-dimensional growth in the doped, higher Al concentration film. This interpretation of the origin of the V-shaped defects is consistent with the observed lowering of the Schottky barrier height in n-doped AlGaN/Ni Schottky diodes.
- Research Organization:
- Lawrence Berkeley National Lab., CA (US)
- Sponsoring Organization:
- USDOE; US Department of the Navy, Office of Naval Research (ONR); National Science Foundation (NSF)
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 20104560
- Resource Relation:
- Conference: 1999 Materials Research Society Fall Meeting, Boston, MA (US), 11/28/1999--12/03/1999; Other Information: PBD: 2000; Related Information: In: GaN and related alloys -- 1999. Materials Research Society symposium proceedings, Volume 595, by Myers, T.H.; Feenstra, R.M.; Shur, M.S.; Amano, Hiroshi [eds.], [1050] pages.
- Country of Publication:
- United States
- Language:
- English
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