Growth Rate Of AlN Research Articles

Modeling analysis of AlN and AlGaN HVPE

AbstractComprehensive model of AlN and AlGaN HVPE is developed. The model combines detailed description of the transport processes and quasi‐thermodynamic model of surface kinetics at the Al/Ga metal surfaces and AlN/AlGaN crystal surfaces. It is shown with the model that HCl dominantly converts into trichloride AlCl3 in the Al source but into monochloride GaCl in the Ga source. Then, AlN grows from AlCl3 under essentially non‐equilibrium conditions while GaN – from GaCl under near‐equilibrium conditions. The revealed differences between the AlN and GaN growth features explain many experimentally observed phenomena, including a sharp saturated behavior of the AlN growth rate in variation of the precursors flow rates and a strong effect of carrier H2 on the AlGaN composition. Generally, the model predicts a high sensitivity of the AlGaN composition to variation of the species flow rates due to their effect on the Ga incorporation. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Surface Morphology of AlN Epitaxial Layer Grown on Various SiC Substrates by Sublimation Closed Space Technique

A sublimation epitaxial method, referred to as the Closed Space Technique (CST) was adopted to produce AlN epitaxial layers. In this study, we report the surface morphology of AlN epitaxial layer grown on various substrates such as 3C-SiC (100), 4H-SiC (0001) with 8o off-axis (0001) plane tilted toward the <11 2 0> direction and on-axis 4H-SiC (0001). An average growth rate of AlN layer at 2350oC in 500 Torr of N2 was measured to be about 6μm/hr. While AlN layer grown on the 3C-SiC (100) substrate at 2350oC exhibited polycrystalline structure, AlN epitaxial layer grown on on-axis and off-axis 4H-SiC (0001) substrates had highly c-axis oriented epitaxial structure. In particular, the stacked structure of hexagonal plates was observed on off-axis substrate and the size of the hexagonal plates increased with growth time. Hexagonal plates were observed to be coalesced and the step-bunching was finally disappeared.

Influence of polymer formation on metalorganic vapor-phase epitaxial growth of AlN

A modeling of reaction pathways in a TMAl/NH 3/H 2 system including parasitic and polymeric reactions for computational simulations was constructed to study temperature and pressure dependences of growth rates and gas-phase chemistry in metalorganic vapor-phase epitaxial growth of AlN. AlN growth rates calculated were in good agreement with experimental data. Reactive molecules such as MMAlNH and Al–N became the major gas-phase species at the high-temperature range. With increasing pressure, the polymerization of these species was enhanced and AlN growth rate significantly decreased.

Effect of Al incorporation on the AlGaN growth by metalorganic chemical vapor deposition

The effect of Al incorporation on the AlGaN growth by metalorganic chemical vapor deposition is investigated. With the increase of trimethylalluminum (TMAl) flux, the crystal quality becomes worse, and the epilayer surface becomes rougher. An interesting phenomenon is that the growth rate of AlGaN decrease with increasing TMAl flux, which is opposite to the AlN growth rate dependence on the TMAl flux. All these effects are attributed to the different properties of Al atoms due to the higher bond strength of Al–N compared with Ga–N, which lead to lower surface mobility and stronger competitive ability of Al atoms during the growth. The enhancement of the surface mobility of Al is especially important for improving the quality of AlGaN.

Parasitic reaction and its effect on the growth rate of AlN by metalorganic chemical vapor deposition

The Al composition of metalorganic chemical vapor deposition (MOCVD)-grown AlGaN alloy layers is found to be greatly influenced by the parasitic reaction between ammonia (NH 3) and trimethylaluminum (TMAl). The growth process of AlN is carefully investigated by monitoring the in situ optical reflection. The abnormal dependencies of growth rate on growth temperature, reactor pressure, and flux of NH 3 are observed and can be well explained by the effect of parasitic reaction. The increase of growth rate with increasing flux of TMAl is found to depend on the growth temperature and reactor pressure due to the presence of parasitic effect. A relatively low growth temperature and a reduced reactor pressure are suggested for the effective decrease of parasitic reaction during the MOCVD growth of AlN and probably lead to a more effective incorporation of Al into the AlGaN layers.

Study on the Seeded Growth of AlN Bulk Crystals by Sublimation

Seeded growth of AlN single crystals on 6H-SiC substrates by sublimation has been investigated. Pyrocarbon coated graphite crucibles were used. Temperature profile and source-substrate distance have been found to be the most influencing parameters of crystal growth. AlN crystals of maximum dimension 9 mm (length) × 5 mm (width) × 300 µm (thickness) were grown on SiC substrates and the best crystal showed an XRD omega rocking curve FWHM of 4.81 arcmin. AlN nucleated as independent hexagonal islands and coalesced as growth progressed on. Growth rate of AlN grown on C-face SiC has been found to be higher than that on Si-face SiC. Pyrocarbon coated crucibles have been found to be better suited for AlN growth as the impurity incorporation in to crystals due to crucible was less.

Sublimation growth of AlN bulk crystals by seeded and spontaneous nucleation methods

ABSTRACTSingle crystals of AlN have been grown by seeded (on SiC substrates) and unseeded (spontaneous nucleation) sublimation techniques. Tantalum carbide coated graphite crucibles were used. Temperature gradient and source-substrate distance have been found to be the most influencing parameters of crystal growth. AlN crystals of maximum dimension 12 mm (length) × 10 mm (width) × 300 μm (thickness) were grown on 6H-SiC substrates and the best (0002) oriented crystal showed an XRD omega rocking curve FWHM of 4.81 arcmin. AlN nucleated as independent hexagonal islands and coalesced as growth progressed on. Growth rate of AlN grown on C-face SiC has been found to be higher than that on Si-face SiC. Tantalum carbide coated crucibles have been found to be better suited for AlN growth as the impurity incorporation in to the crystals due to crucible was very less. Spontaneously nucleated crystals exhibited an incompleted pyramid-like structure with (1010) and (1100) as their prominent faces.

Experimental and Theoretical Analysis of Heat and Mass Transport in the System for AlN Bulk Crystal Growth

ABSTRACTBulk AlN crystal growth by Physical Vapor Transport (PVT) is studied both experimentally and numerically. This paper presents the analysis of heat and mass transport mechanisms in closed and partially open crucible geometries. The heat transfer in the growth system used at North Carolina State University (NCSU) is simulated. The computed temperature profiles are used in the analysis of mass transport in the growth cell to gain understanding of the effect of species exchange between the crucible and environment on the AlN growth rate. The model predictions are in reasonable agreement with observations.

Layer-by-layer growth of AlN and GaN by molecular beam epitaxy

The conditions for obtaining layer-by-layer growth of (0001) AlN and GaN with wurtzite structure in molecular beam epitaxy (MBE) have been determined by studying reflection high-energy electron diffraction (RHEED) oscillations. For both materials, the growth conditions are optimized when the metal/nitrogen ratio is close to unity. Atomic hydrogen has been found to enhance significantly the AlN growth rate. This effect is tentatively attributed to an increase in the nitrogen incorporation efficiency in the presence of hydrogen.

Diagnostics of dual source reactive magnetron sputter deposition of aluminum nitride and zirconium nitride thin films

The process of reactive sputtering of elemental Al and Zr in an Ar/N2 mixture has been examined by atomic absorption spectroscopy. Results have been presented further supporting the existence of a chemical competition effect during dual source reactive sputtering. The growth of epitaxial AlN film on Si(111) by laser beam interference is monitored in real time, which yielded a measurement of the true growth rate. By correlating the two measurements, a linear proportionality between the true growth rate of AlN and the gas phase Al density has been demonstrated.