Berlin 2012 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 73: GaN: Preparation and Characterization IV

HL 73.4: Vortrag

Donnerstag, 29. März 2012, 10:15–10:30, ER 270

High quality n-GaN with carrier concentrations above 10²⁰ cm^{− 3} using Germanium doping — •Stephanie Fritze, Antje Rohrbeck, Hartmut Witte, Armin Dadgar, and Alois Krost — Institute of Experimental Physics, Otto-von-Guericke-Universität Magdeburg, Germany

For GaN based semiconductor devices, especially for LED manufacturing, a high n-type conductivity is necessary for homogeneous current spreading. Commonly Si is used as n-type dopant in GaN, but it induces additional tensile stress in the GaN layer possibly leading to cracking. Furthermore, exceeding a critical Si doping level of n=5·10¹⁹ cm⁻³ the GaN surface becomes rough. We demonstrate successful Ge doping for highly conductive n-GaN using two different Germanium sources, GeH₄ and iso-butyl-germane (IBGe). The GaN structures were grown on c-sapphire substrates by the MOVPE technique using standard growth conditions. We realized Ge-doping levels up to 2.5·10²⁰ cm⁻³ without any tensile stress enhancement. All Ge-doped GaN structures show a smooth and crack-free surface in Nomarski microscopy. Even at carrier concentrations of n=2.5·10²⁰ cm⁻³, as determined by Hall effect measurements, no surface morphology degradation was visible. In a doping range between 1·10¹⁸ and 5·10¹⁹ cm⁻³ the XRD ω-FWHM is similar between Si-doped and Ge-doped GaN. But with further increasing the carrier concentration the crystalline quality abruptly improves at a doping concentration around 1·10²⁰cm⁻³. In this case both Ge dopant sources show equal characteristics.