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Microstructure of highly p-type doped GaN sub-contact layers for low-resistivity contacts
Published online by Cambridge University Press: 01 February 2011
Abstract
The effect of a highly Mg doped subcontact layer on top of GaN grown by metal organic vapor phase epitaxy and its interface to a Pd/Au contact layer was investigated by means of transmission electron microscopy and electrical characterization techniques. Use was made of prior investigations of the Mg doping characteristics, which showed the existence of a segregation related defect free layer even for doping levels as high as 5×10−19cm−3, which thickness depends on the Mg to Ga molar precursor flow ratio. For a given subcontact layer thickness of 15 nm a critical precursor molar flow ratio of 0.035 resulted in a smooth surface showing an interfacial layer indicating a Pd/Ga alloying. This layer resulted in a contact resistivity as low as 2×10−5 Ωcm2. For a flow ratio of 0.070 the surface was found to be rough due to defect formation resulting in a contact resistivity as high as 10−3 Ωcm2 similar to the value obtained without subcontact layer. Moreover, the metallization layer showed in all cases a texture of the {111} lattice planes with respect to the {0002} planes of the GaN.
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- Copyright © Materials Research Society 2005