Epitaxial Growth Of AlN Films Research Articles

Preparation of single crystalline AlN thin films on ZnO nanostructures by atomic layer deposition at low temperature

The growth of hetero-epitaxial ZnO-AlN core–shell nanowires (NWs) and single crystalline AlN films on non-polar ZnO substrate at temperature of 380 °C by atomic layer deposition (ALD) was investigated. Structural characterization shows that the AlN shells have excellent single-crystal properties. The epitaxial relationship of [0002]ZnO//[0002]AlN, and [10−10]ZnO//[10−10]AlN between ZnO core and AlN shell has been obtained. The ZnO NW templates were subsequently removed by annealing treatment in forming gas, resulting in ordered arrays of AlN single-crystal nanotubes. The impact factors on the epitaxial growth of AlN films are thoroughly investigated. It turned out that the growth parameters including lattice mismatch between substrate and AlN, growth temperature, and the polarity of ZnO substrate play important roles on the growth of single-crystal AlN films by ALD. Finally, non-polar AlN films with single-crystalline structure have been successfully grown on m-plane ZnO (10−10) single-crystal substrates. The as-grown hollow AlN nanotubes arrays and non-polar AlN films with single-crystalline structures are suggested to be highly promising for applications in nanoscale devices. Our research has developed a potential method to obtain other inorganic nanostructures and films with single-crystalline structure at fairly low temperature.

Investigation on halide vapor phase epitaxial growth of AlN using N2 as N source

Abstract Epitaxial growth of AlN films on sapphire substrates prepared by halide vapor phase epitaxy (HVPE) using N2 as N source is reported. The effects of V/III ratio on the growth rate, surface morphology and crystal quality of AlN films are systematically investigated. Compared with traditional HVPE using NH3 as N source, the growth rate of AlN films here increased linearly instead of decrease exponentially as increasing input V/III ratio. The surface morphology of the as-grown AlN films exhibited a periodic stripe structure at low V/III ratio and exhibited a pit-like or grid-like structure at high V/III ratio. The effect of V/III ratio on crystal quality varied under different HCl flow rate. The full width at half maximum (FWHM) of the (0002)- and (10-12)- plane X-ray rocking curves (XRCs) were 108–480 and 495–1083 arcsec, respectively, depending on both the V/III ratio and the growth rate of AlN films.

Improved Epitaxy of AlN Film for Deep-Ultraviolet Light-Emitting Diodes Enabled by Graphene.

The growth of single-crystal III-nitride films with a low stress and dislocation density is crucial for the semiconductor industry. In particular, AlN-derived deep-ultraviolet light-emitting diodes (DUV-LEDs) have important applications in microelectronic technologies and environmental sciences but are still limited by large lattice and thermal mismatches between the epilayer and substrate. Here, the quasi-van der Waals epitaxial (QvdWE) growth of high-quality AlN films on graphene/sapphire substrates is reported and their application in high-performance DUV-LEDs is demonstrated. Guided by density functional theory calculations, it is found that pyrrolic nitrogen in graphene introduced by a plasma treatment greatly facilitates the AlN nucleation and enables fast growth of a mirror-smooth single-crystal film in a very short time of ≈0.5 h (≈50% decrease compared with the conventional process), thus leading to a largely reduced cost. Additionally, graphene effectively releases the biaxial stress (0.11 GPa) and reduces the dislocation density in the epilayer. The as-fabricated DUV-LED shows a low turn-on voltage, good reliability, and high output power. This study may provide a revolutionary technology for the epitaxial growth of AlN films and provide opportunities for scalable applications of graphene films.

High-quality AlN epitaxy on nano-patterned sapphire substrates prepared by nano-imprint lithography.

We report epitaxial growth of AlN films with atomically flat surface on nano-patterned sapphire substrates (NPSS) prepared by nano-imprint lithography. The crystalline quality can be greatly improved by using the optimized 1-μm-period NPSS. The X-ray diffraction ω-scan full width at half maximum values for (0002) and (102) reflections are 171 and 205 arcsec, respectively. The optimized NPSS contribute to eliminating almost entirely the threading dislocations (TDs) originating from the AlN/sapphire interface via bending the dislocations by image force from the void sidewalls before coalescence. In addition, reducing the misorientations of the adjacent regions during coalescence adopting the low lateral growth rate is also essential for decreasing TDs in the upper AlN epilayer.

Epitaxial growth of AlN films on sapphire via a multilayer structure adopting a low- and high-temperature alternation technique

Epitaxial growth of AlN films on c-sapphire using a multilayer structure has been investigated by metal–organic chemical vapor deposition adopting multiple alternation cycles of low- and high-temperature (LT–HT) growth. It is found that the surface morphology and crystal quality can be greatly improved using three alternation cycles with X-ray diffraction ω-scan full width at half maximum values of 311 and 548 arcsec for the (0002) and (10−12) peaks, respectively, which are induced by the alternation of the three-dimensional (3D) and two-dimensional (2D) growth modes caused by the LT–HT process. The first 3D–2D cycle is found to play a major role in threading dislocation reduction, while the second and third cycles mainly account for tensile stress relaxation.

Expansion of lattice constants of aluminum nitride thin film prepared on sapphire substrate by ECR plasma sputtering method

Wurzite aluminum nitride is prepared on a c-plane sapphire substrate by electron cyclotron resonance plasma-enhanced sputtering deposition (ECR sputtering). Atomic force microscopy (AFM) showed flat AlN thin-film surfaces, and X-ray diffraction (XRD) analysis verified the epitaxial growth of AlN films with the full-width at half-maximum (FWHM) of the rocking curve of 0.025 deg on the film with the thickness of 100 nm. XRD analysis also verified the change in the peak position for the AlN film along both out-of-plane and in-plane directions. The effect of lattice constants on the energy gap was theoretically estimated by the first principles method.

Epitaxial growth of AlN films on Rh ultraviolet mirrors

Epitaxial growth of AlN films on mirror polished Rh(111) substrates, with high reflectivity in the ultraviolet (UV) region and high thermal conductivity, was demonstrated using a low temperature growth technique employing pulsed laser deposition. It was found that AlN(0001) grows epitaxially on Rh(111) at 450°C with an in-plane epitaxial relationship of AlN[112¯0]‖Rh[11¯0] Electron backscattering diffraction observations revealed that neither 30° rotational domains nor cubic phase domains were present in the AlN. X-ray reflectivity measurements revealed that no interfacial layer was present between the AlN films and Rh substrates and that the heterointerface was atomically abrupt, indicating that the Rh substrate still functioned as an UV mirror, even after AlN growth.

Low wet etching rates of ZnO films prepared by sputtering of mixed ZnO and AlN powder targets

ZnO films codoped with Al and N have been prepared by radio frequency magnetron sputtering in an Ar atmosphere, using targets of mixtures of ZnO and AlN powders. The Al-doped ZnO films are transparent, whereas the films codoped with Al and N are colored. The Al- and N-concentrations in the colored films are estimated to be 4–7 at.% and 1–2 at.%, respectively. No enhancement of the carrier density is seen in the colored ZnO films, whereas the colored films exhibit lower etching rates of 3–5 nm/s in a 0.1 M HCl solution, in comparison with the Al-doped ZnO films. For the colored film, the anisotropic grain growth occurs, and cubic grains are produced after etching. The low etching rates of the colored films are ascribed to the epitaxial growth of AlN films on the surfaces of ZnO grains, rather than the incorporation of Al–N and Al–O bonds into the ZnO lattice.

Epitaxial growth of AlN films on single-crystalline Ta substrates

We have demonstrated the first epitaxial growth of AlN films on single-crystalline Ta substrates by the use of a low-temperature growth technique based on pulsed laser deposition (PLD). Although previous AlN films grown on Ta(100) and (111) substrates have exhibited quite poor crystallinity, an epitaxial AlN(0001) film with an in-plane epitaxial relationship of AlN[112¯0]//Ta[001] has been obtained on a Ta(110) substrate at a growth temperature of 450 °C. We found that the full-width at half-maximum values for the crystal orientation distribution in the tilt and twist directions of the AlN film were 0.37° and 0.41°, respectively. Grazing-incidence X-ray reflection (GIXR) and X-ray photoelectron spectroscopy (XPS) measurements have revealed that the AlN/Ta heterointerface is quite abrupt, and that its abruptness remains unchanged even after annealing at 1000 °C.

Epitaxial growth of AlN films on Si substrates by ECR plasma assisted MOCVD under controlled plasma conditions in afterglow region

Wurtzite-type aluminum nitride (h-AlN) films were epitaxially grown on off-axis Si (111) substrates by electron–cyclotron–resonance plasma-enhanced metalorganic chemical vapor deposition (ECRMOCVD) using trimethylalminum (TMA) and ammonia (NH 3) as source gases. Plasma space potential in the growth chamber was lowered by setting the magnetic field distribution as a mirror field. For the growth of h-AlN with excellent crystallinity on Si substrates, nitridation of the substrate surface, growth of a low-temperature (LT) buffer layer, and epitaxial growth of AlN films were performed under a mirror field condition in a growth chamber. Thermal nitridation at 1050°C prior to the epitaxial growth appreciably improved the crystallinity of AlN films. The growth of buffer layer at temperatures below 650°C was not so effective for the improvement of the crystallinity and crystal orientation of AlN epitaxial layer. The proportion of domain including stacking faults and that whose c-axis was parallel to the substrate surface was very small ( I (0002)/( I (10–10)+ I (10–11))>700), irrespective of the gas feed ratio of N source to Al source (NH 3/TMA) during the epitaxial growth process. Under a small gas feed ratio (NH 3/TMA<200), however, the diffraction peak intensities from the non-epitaxial domains became large.

Conducting (Si-Doped) Aluminum Nitride Epitaxial Films Grown by Molecular Beam Epitaxy

ABSTRACTAs a member of the III-V nitride semiconductor family, AlN, which has a direct energygap of 6.2eV, has received much attention as a promising material for many applications. However, despite the promising attributes of AlN for various semiconductor devices, research on AlN has been limited and n-type conducting AlN has not been reported. The objective of this research was to understand the factors impacting the conductivity of AlN and to control the conductivity of this material through intentional doping. Prior to the intentional doping study, growth of undoped AlN epilayers was investigated. Through careful selection of substrate preparation methods and growth parameters, relatively low-temperature molecular beam epitaxial growth of AlN films was established which resulted in insulating material. Intentional Si doping during epilayer growth was found to result in conducting films under specific growth conditions. Above a growth temperature of 900°C, AlN films were insulating, however, below a growth temperature of 900°C, the AlN films were conducting. The magnitude of the conductivity and the growth temperature range over which conducting AlN films could be grown were strongly influenced by the presence of a Ga flux during growth. For instance, conducting, Si-doped, AlN films were grown at a growth temperature of 940°C in the presence of a Ga flux while the films were insulating when grown in the absence of a Ga flux at this particular growth temperature. Also, by appropriate selection of the growth parameters, epilayers with n-type conductivity values as large as 0.2 Ω−1 cm−1 for AlN and 17 Ω−1cm−1 for Al0.75Ga0.25N were grown in this work for the first time.