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Posted: Feb 21, 2011
Strain Engineering Controlled by EpiCurveTT: GaN:Ge Layers on Silicon
(Nanowerk News) GaN based epitaxy on silicon (Si) is very challenging because
of the thermal mismatch between GaN and Si, which causes
extreme tensile stress after cooling. For such applications
LayTec's EpiCurveŽTT is the tool of choice for a precise in-situ
Fig. 1: In-situ curvature measurements with EpiCurveŽTT of GaN/Si with Si doping (solid line) and Ge doping (dashed line).
Fig. 1 shows curvature measurement on two differently doped
GaN/Si samples. The downward slope after the LT-AlN
interlayer growth indicates compressive stress. With the
addition of Si as dopant, the slope inverts (solid line), the Si
doping causes tensile stress and during cooling the sample
cracks. In the case of Ge doping, however, the curvature slope
remains unchanged (dashed line) and the sample remains
Photoluminescence spectra of the Ge doped GaN shows a
doubled luminescence intensitiy compared with the Si doping.
This proves good material quality of the approx. 1.6 µm
thick GaN structure.
According to Armin Dadgar of OvG University, "the idea to
dope GaN-on-silicon with an alternative dopant is quite old.
But now, with strain control and engineering with mixed dopants,
EpiCurveŽTT gives a new impulse for GaN/Si device