Mechanisms of strain reduction in GaN and AlGaN/GaN epitaxial layers

Book · Wed Dec 31 04:00:00 EST 1997

OSTI ID:581065

Gfroerer, O; Schluesener, T; Haerle, V; Scholz, F; Hangleiter, A ^[1]

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1. Univ. Stuttgart (Germany). Physikalisches Inst.

The authors have investigated Al{sub 0.12}Ga{sub 0.88}N layers with and without a 1 {micro}m GaN buffer, grown on the c-face of {alpha} {minus} Al{sub 2}O{sub 3} substrate with an intermediate AlN nucleation layer grown by LP-MOVPE. The authors used spatially resolved cathodoluminescence spectroscopy at a temperature of 8K to investigate the strain and the homogeneity of composition that can be determined from the energy of the luminescence peak. The larger thermal expansion coefficient of the sapphire in comparison to the nitrides leads to a biaxial compressive strain of the upper GaN layer when cooling down from growth temperature. For AlGaN layers directly grown on the nucleation layer this cannot be confirmed. The layer stays relaxed and fluctuations in the aluminium composition of 0.4% can be observed. When growing an intermediate GaN buffer, the AlGaN layer gets tensilely strained. This strain is of elastic nature and microcracks can be observed preferentially at the edges due to the smaller lattice constant of AlGaN in comparison to GaN. Even detaching of the AlGaN layers grown on the buffer can be observed. In the regions without cracks the layers are quite homogeneous. A deformation potential of (19 {+-} 4) eV was estimated for Al{sub 0.12}Ga{sub 0.88}N.

• OSTI ID: 581065
• Report Number(s): CONF-961202--; ISBN 1-55899-353-3
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM NITRIDES
ALUMINIUM OXIDES
CHEMICAL COMPOSITION
DEFORMATION
EXPERIMENTAL DATA
GALLIUM NITRIDES
MICROSTRUCTURE
STRESSES
VAPOR PHASE EPITAXY