Strain-free GaN thick films grown on single crystalline ZnO buffer layer with in situ lift-off technique

Abstract

Strain-free freestanding GaN layers were prepared by in situ lift-off process using a ZnO buffer as a sacrificing layer. Thin Zn-polar ZnO layers were deposited on c-plane sapphire substrates, which was followed by the growth of Ga-polar GaN layers both by molecular beam epitaxy (MBE). The MBE-grown GaN layer acted as a protecting layer against decomposition of the ZnO layer and as a seeding layer for GaN growth. The ZnO layer was completely in situ etched off during growth of thick GaN layers at low temperature by hydride vapor phase epitaxy. Hence freestanding GaN layers were obtained for the consecutive growth of high-temperature GaN thick layers. The lattice constants of freestanding GaN agree with those of strain-free GaN bulk. Extensive microphotoluminescence study indicates that strain-free states extend throughout the high-temperature grown GaN layers.

Highly oriented GaN films grown on ZnO buffer layer over quartz substrates by reactive sputtering of GaAs target

“…The crystallite tilt of~2.5°in sputtered GaN film on ZnO buffer layer over quartz substrate, is comparable to the reported value of~2°for GaN films sputter deposited on ZnO/Si substrates from a Ga 2 O 3 target [51]. The measured value of tilt is about an order of magnitude higher than the reported values (from (0002) rocking curve measurements) for epitaxial GaN films grown over ZnO buffer layers on sapphire substrates by MBE [48], MOCVD [44] and PLD [50,57] techniques. Phi (ϕ) scans of asymmetric (1011) reflections were also carried out on both the films.…”

“…High quality epilayers of GaN have also been deposited on ZnO buffer layer over sapphire substrates, using this approach [44,48,49]. There are also a few reports on the use of ZnO as a buffer layer in the growth of GaN films by sputtering, using GaN [50] and Ga 2 O 3 [51] targets.…”

MOVPE growth of GaN around ZnO nanopillars

“…This may be in particular helpful to realize a p-n junction in planar [1] or coaxial [2] form because of the much better p-doping properties of GaN as compared to ZnO. Heterostructures of GaN on ZnO can also be used as a template for the hydride vapor phase epitaxial growth of thick GaN layers [3] in which the ZnO may work as an in situ separation layer for a free-standing GaN bulk crystal. Furthermore, the growth of hollow GaN nanotubes [4] after in situ removal of ZnO nanopillars may offer an opportunity to realize novel 1D quantum structure devices for nano-photonics, nano-electronics, and biochemical sensing applications.…”

Fabrication of a freestanding GaN layer by direct growth on a ZnO template using hydride vapor phase epitaxy

“…Therefore, it is important to develop simpler ways to grow and separate the GaN layer. ZnO has attracted considerable attention as a sacrificial interlayer, which facilitates a simple separation technique [9]. ZnO satisfies the fundamental requirements for epitaxial growth: the same crystal structure and a small lattice mismatch of only 1.8% (c-axis) and 0.4% (a-axis).…”