This paper reports a novel selective growth method for growing crack-free semi-polar (1-101) GaN on 7°-off (001) Si
substrates by adding SiO2 stripes in perpendicular to the V-grooves on Si. This method can effectively reduce the thermal
stress between GaN and Si substrate so that crack-free (1-101) GaN films as thick as 1 μm is achieved after coalescence
even without an AlN interlayer. Cathodoluminescence measurements show the presence of low dislocation density areas,
which can be attributed to the bending of dislocations toward to the [1-100] and [11-20] directions during the facet
growth.
Aluminum nitride is a material of great potential for high power electronic devices, UV photonic devices as well as
acoustic devices. However, the lack of a good crystal growth technology for bulk material and substrate hinders the
development of these AlN-based devices. While AlN has been successfully grown on sapphire substrate for some time,
the presence of a large number of dislocations in the material is still a major barrier to overcome [1]. In this work, we
demonstrate a low-dislocation-density AlN template on sapphire by inserting an AlN interlayer by metal-organic
chemical vapor deposition. The main idea of our approach is to change the growth mode in the course of the epitaxial
growth by decreasing growth temperature and changing V/III ratio. As the growth mode changes, dislocations tend to be
redirected and/or form dipole half loops via annihilation processes [2]. The etch-pit-density of the AlN templates is
reduced from 3.6×109 cm-2 to 1.7×109 cm-2. Accordingly, the full width at half maximum of the (0002) x-ray rocking
curve is reduced from 37 arcsec to 12 arcsec. The result indicates that the AlN template has low screw and mixed type
dislocations. AlGaN/GaN Schottky diodes fabricated on this high quality AlN template exhibit very high breakdown
voltage (> 2000 V), which sets a record-high figure of merit of 1.15 GW/cm2.
We demonstrate that Ti/Al/Cr/Mo/Au ohmic contact has an extremely smooth surface morphology of 29.0 nm and
a low specific contact resistivity (ρc) of 1.1×10-6 ohm-cm2 on n-type AlGaN/GaN heterostructures. The use of Cr
interlayer in Ti/Al/Cr/Mo/Au contacts leads to significantly improved contact morphology without any degradation on
the contact resistance. This is attributed to the reduced inter-diffusion and reaction between the layers in the contact
stack.
The authors report on the growth of GaN on AlGaN/(111)Si micropillar array by metal-organic chemical vapor
deposition. Using the substrates with micropillar array, 2 μm-thick GaN films without cracks can be achieved.
Transmission electron microscopy, atomic force microscopy, and micro-Raman studies indicate that the dislocation
density and residual stress of the GaN grown on micropillar array are also reduced. The results reveal the potential of this
type of substrates for growing GaN-based devices as well as preparing GaN freestanding substrates.
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