Growth Rate Of AlN Research Articles

Study of AlN growth using AMEC Prismo HiT3 MOCVD reactor

Effect and mechanism of carrier gas velocity, V/III ratio, and carrier gas velocity match of group III to group V (MO VM) on AlN growth rate (GR) were investigated in depth by experiment and computational fluid dynamics (CFD) simulation in Prismo HiT3 MOCVD platform. It is found that AlN growth rate increases with hydrogen flow rate at first, reaches saturation and then shows a monotonic decrease trend. The specific value of turning point depends on the equipment and process. At constant total flow rate of 160 slm, GR increases with MO VM by suppressing parasitic reaction, but uniformity show a deteriorate trend due to the occurrence of turbulence and loss of uniform boundary layer. High quality 4-μm-thick AlN films with improved crystalline quality and atomic smooth surfaces were achieved on nano-patterned sapphire substrates with a growth rate of 0.82 um/hr. The full width at half maximum of the X-ray rocking curve was 162/305 arcsec for (002)/(102) planes with total dislocation density ∼ 109 cm−2.

Reduction of parasitic reaction in high-temperature AlN growth by jet stream gas flow metal–organic vapor phase epitaxy

AlGaN-based deep ultraviolet light-emitting diodes (LEDs) have a wide range of applications such as medical diagnostics, gas sensing, and water sterilization. Metal–organic vapor phase epitaxy (MOVPE) method is used for the growth of all-in-one structures, including doped layer and thin multilayers, using metal–organic and gas source raw materials for semiconductor devices. For AlN growth with high crystalline quality, high temperature is necessary to promote the surface migration of Al atoms and Al-free radicals. However, increase in temperature generates parasitic gas-phase prereactions such as adduct formation. In this work, AlN growth at 1500 °C by a stable vapor phase reaction has been achieved by jet stream gas flow metal–organic vapor phase epitaxy. The AlN growth rate increases with gas flow velocity and saturates at ~ 10 m/s at room temperature. Moreover, it is constant at an ammonia flow rate at a V/III ratio from 50 to 220. These results demonstrate the reduction in adduct formation, which is a typical issue with the vapor phase reaction between triethylaluminum and ammonia. The developed method provides the in-plane uniformity of AlN thickness within 5%, a low concentration of unintentionally doped impurities, smooth surface, and decrease in dislocation density because of the suppression of parasitic reactions.

The Effect of Si (111) Substrate Surface Cleaning on Growth Rate and Crystal Quality of MOVPE Grown AlN

In this work, the effect of Si (111) substrate surface cleaning by RCA (Radio Corporation of America) method on growth rate and crystalline quality of epitaxially grown AlN thin films by MOVPE (Metal Organic Vapor Phase Epitaxy) technique is investigated. In situ reflectance system and high resolution X-ray diffraction (HRXRD) technique are used for the analysis of growth rate and crystal quality of epitaxial AlN layers, respectively. Also, The Raman measurement is done to show the effect of the RCA cleaning procedure on the position of the peaks that occurred in the Raman spectra. The results have shown that the surface cleaning of Si (111) substrate by the RCA method removes the oxide layer formed on the surface, also helps to decrease the parasitic reactions and increases the adatom efficiency, results in an increased growth rate of the AlN layer. Besides, surface cleaning of Si (111) substrate by the RCA method has reduced the FWHM value ~5% for ω-2θ scan and ~60% for ω scan of AlN epilayer, indicating an improvement in crystal quality.

Heteroepitaxial AlN growth on c-plane sapphire substrates by ammonia-free high temperature metalorganic chemical vapor deposition

AlN films were hetero-epitaxially grown on c-plane sapphire substrates by ammonia-free high temperature metalorganic chemical vapor deposition (AFHT-MOCVD). The dependence of the AlN growth rate on the flow rate of source gases (H2, N2 and trimethylaluminum (TMA)) and the growth temperature were systematically investigated. The maximum AlN growth rate up to ∼4.0 μm/hour was obtained at the present growth conditions. Based on the experimental results, the possible mechanisms in the AFHT-MOCVD growth concerning the gas reactions are qualitatively discussed. The as-grown AlN epilayers were characterized by high-resolution X-ray diffraction (HRXRD), scanning electron microscope (SEM) and scanning transmission electron microscope (STEM). The narrow full width at half maximum (FWHM) values of symmetric (0002) and asymmetric (10–12) AlN diffractions are obtained ((0002): 211 arcsec, (10–12): 325 arcsec from a ∼3 μm thick AlN epilayer), showing the potential of the growth technique for the high quality AlN growth.

Influences of Powder Source Porosity on Mass Transport during AlN Crystal Growth Using Physical Vapor Transport Method

We developed a two-dimensional (2D) transport model to investigate mass transport during bulk AlN crystal growth via the physical vapor transport (PVT) process using the finite element method (FEM), taking the powder source porosity, buoyancy, and vapor diffusion into account. The porosity effects of the powder source on mass transport under various growth conditions were investigated in detail. The simulation results show that the porosity of the powder source significantly affects the mass transport process during AlN sublimation growth. When the porosity of the powder source decreases, the growth rate becomes more uniform along the seed deposition surface, although the sublimation rate and crystal growth rate decrease, which can be attributed to the reduced specific surface area of the powder source and the reduced flow rate of Al vapor in the powder source. A flat growth interface can be achieved at a porosity of 0.2 under our specific growth conditions, which in turn facilitate the growth of high-quality AlN crystals and better yield. The decomposition of the powder source and the transport of Al vapor in the growth chamber can be suppressed by increasing the pressure. In addition, the AlN growth rate variation along the deposition surface can be attributed to the Al vapor pressure gradient caused by the temperature difference in the growth chamber.

Broadband Ultraviolet Emission from 2D Arrays of AlGaN Microstructures Grown on the Patterned AlN Templates

Broadband ultraviolet (UV) emission is achieved using AlGaN microstructure 2D arrays. 2D arrays of trenches are initially formed on AlN templates on sapphire (0001) substrates. AlGaN‐based quantum wells (QWs) are subsequently regrown on top of the patterned templates. Bunched steps are formed within the trench, inducing variations in the Al composition and AlGaN thickness in the QWs. Regions with and without bunched steps coexist and cause emission wavelength variations. The formation mechanism of bunched steps is attributed to the position‐dependent AlN growth rate due to variations of the source–precursor flow within narrow trenches.

Analysis of growth rate and crystal quality of AlN epilayers by flow-modulated metal organic chemical vapor deposition

Abstract AlN templates have been grown on sapphire by flow-modulated metal organic chemical vapor deposition (MOCVD). By analyzing the TMAl duty ratio R, TMAl utilization ratio β and parasitic reaction ratio α, we obtained the quantitative relationship between flow-modulated modes and growth rate, and then proposed two kinds of flow-modulated modes to increase the growth rate of AlN. Besides, we found the continuous growth in flow-modulated mode can transform the AlN growth mode from the step-bunching growth into the two-dimension growth and accordingly improve the crystal quality of AlN. Finally, the AlN template with a relatively fast growth rate (0.98 μm/h) and flat surface morphology (RMS = 0.5 nm) was obtained by NH3 pulse-flow mode with a small duty ratio of NH3.

Fast Growth of Smooth AlN in a 3 × 2″ Showerhead‐Type Vertical Flow MOVPE Reactor

The conditions required for a high growth rate of AlN in a 3 × 2″ showerhead‐type vertical flow metalorganic vapor phase epitaxy (MOVPE) reactor are studied. It is found that at the standard growth conditions (low V/III, 50 mbar, 1110 °C, H2), the growth rate linearly increases with the trimethylaluminium (TMAl) flow rate until about 280 μmol min−1 with some drop of precursor utilization efficiency at higher pressures. While the pre‐reaction of TMAl with NH3 at 140 μmol min−1 of TMAl is still not a major issue, it is not possible, however, to maintain a smooth AlN surface morphology during this “fast” growth. To suppress the surface morphology deterioration, the growth pressure requires optimization. An increase of the growth pressure, to 75 mbar, is found to be critical to grow 20+ μm of smooth AlN at a rate of about 3.6 μm h−1 on bulk AlN substrates.

A kinetics model for MOCVD deposition of AlN film based on Grove theory

Based on Grove theory, a kinetic model for MOCVD deposition of AlN film was proposed and built in this paper. Physical and chemical processes, e.g., gas phase transport, surface adsorption, surface chemical reactions, as well as the gas phase reactions in boundary layer were analyzed in the kinetic model. Based on this model, the effects of substrate temperature and chamber pressure on the growth rate of AlN film were investigated, as well as the corresponding mechanisms. Meanwhile, the dependences of AlN growth rate and temperature, pressure for three types of reaction pathways were also analyzed. The simulated results provide an important insight into the optimizing of AlN growth with appropriate temperature and pressure in experiment.

Strong impact of the initial III/V ratio on the crystalline quality of an AlN layer grown by rf-plasma-assisted molecular-beam epitaxy

The initial Al/N ratio for AlN growth of plasma-assisted molecular-beam epitaxy without plasma stabilization is investigated. The in situ growth rate of AlN gradually increased and its temporal variation corresponded to that of nitrogen atoms, which indicated that the initial Al/N ratio was excessively Al-rich. For AlN growth, such a high-Al/N-ratio condition resulted in a three-dimensional growth mode in the initial stage of the growth, and AlN with high threading dislocation density was obtained. By controlling the initial Al/N ratio by introducing a short standby time, the resulting two-dimensional initial growth mode leads to high-quality growth of AlN.

Effect of hydrogen carrier gas on AlN and AlGaN growth in AMEC Prismo D-Blue® MOCVD platform

Effect of hydrogen flow rate on AlN and AlGaN growth is investigated in AMEC Prismo D-Blue® MOCVD platform. It is found that AlN growth rate increases with the increase of hydrogen flow rate. Al composition in AlGaN material increases initially with the increase of hydrogen flow rate at relatively low hydrogen flow rates (<120slm) and then saturates at high hydrogen flow rates. GaN partial growth rate shows a “U” shaped profile. Computational fluid dynamics (CFD) simulation of AlN growth is performed to understand the growth mechanism. The simulation results indicate that higher hydrogen flow rate could suppress the parasitic reaction and particle formation during AlN growth. Thus more source gases can be transported to the wafer surface, resulting in the increase of AlN growth rate.

Effects of carrier gas ratio and growth temperature on MOVPE growth of AlN

AbstractThe strong demand for high‐efficiency light‐emitting diodes in the deep‐ultraviolet region and for sensors has led to renewed interest in the growth of high‐quality AlN. However, the growth of high‐quality AlN is extremely difficult owing to the low surface migration rate of Al adatoms. In this study, the effects of the carrier gas ratio and growth temperature on the growth rate of AlN are examined with the aim of optimizing the growth conditions of high‐temperature AlN. AlN epilayers were grown on sapphire substrates by metal‐organic vapor phase epitaxy (MOVPE) at a growth temperature of 1430 °C with a medium‐temperature AlN layer grown at 1100 °C. A combination of H2 and N2 was used as the carrier gas in the growth of AlN, and the ratio of H2 to N2 in the carrier gas was changed to examine its effect on the growth of AlN. Under all growth conditions, crack‐free and smooth surfaces at the atomic level with an extremely small tilt were obtained. The growth rate decreased with increasing growth temperature and ratio of H2 in the carrier gas. This suggests that the high temperature and the H2 carrier gas inhibit the adsorption of atoms. Also, with increasing ratio of N2 in the carrier gas, the radius of curvature of the AlN layer increased and the compressive strain decreased. The reduction of compressive strain and increase in curvature of the AlN layer were due to an increase in the number of dislocations. (© 2012 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

High growth rate MOVPE of Al(Ga)N in planetary reactor

Possibility of AlN growth by MOVPE in a planetary reactor with high growth rate was investigated. Growth was performed on (0001) Al2O3 substrates at the reactor pressure of 100mbar. It was shown that deposition rate is close to diffusion limit at low NH3 flows and reduces abruptly above a certain threshold value of NH3 due to gas-phase parasitic reactions. At constant V/III ratio of 1.5–2, AlN growth rate dependence on TMAl flow was linear and a maximum growth rate of 8.6μm/h was achieved. Process modeling allowed predicting and explaining the trends related to the onset of parasitic chemistry for various V/III ratios and other growth conditions. Surface morphology planarization was achieved by either (1) NH3 flow rate reduction or (2) TMGa injection after the layer with thickness of 75–300nm was grown. The second approach looks more fruitful resulting in atomically flat Al(Ga)N layers with a 2μm/h growth rate. For the conditions (high temperature, low NH3 and high H2 concentration) used Ga acts mostly as surfactant (Ga content in Al(Ga)N is about 3–5%).

The effect of ammonia flow in the AlN spacer on the electrical properties of InAlN/AlN/GaN HEMT structures

AbstractDuring the past few years it has been reported that a thin AlN spacer of few nanometers needs to be inserted in InAlN/GaN high electron mobility transistors (HEMTs) to obtain high 2DEG carrier mobility. This work presents a systematic study of the effects of varying the ammonia flow in the AlN spacer of InAlN/AlN/GaN HEMTs grown by low pressure metalorganic vapour phase epitaxy (LP‐MOVPE). The strain state, the surface roughness and the growth rate of AlN were found to be dependent on the V/III ratio. In addition the ammonia flow in the interlayer has a strong impact on the structural properties of the subsequent InAlN barrier layer and on the electrical properties of the structure. A sheet resistance as low as 327 Ω/□ with a sheet carrier density of 1.5 × 1013 cm−2 has been obtained at room temperature.

AlInN MOVPE: growth chemistry and analysis of trends

Comprehensive model of AlInN Metal-Organic Vapor Phase Epitaxy (MOVPE) accounting for the gas-phase and surface chemistry including parasitic reactions/particle formation is developed. Experimental data and modeling results suggest that as V/III ratio increases from several tens (growth of pure AlN) to several thousands (growth of AlInN), the partial AlN growth rate decreases even in the absence of strong particle formation. This effect is associated with the formation of heavy molecular weight/low diffusivity gas-phase dimer species at high ammonia concentration. At elevated pressures growth rate decreases with pressure at a weakly changing composition, which is related to the gas-phase losses of In- and Al-containing species due to reaction with AlN particles. Model allows the prediction of both the AlInN growth rate and composition versus group-III flow rates, temperature, and pressure.

Influence of the interface on growth rates in AlN/GaN short period superlattices via metal organic vapor phase epitaxy

AlN/GaN short period superlattices are well suited for a number of applications including, but not limited to, digital alloys, intersubband devices, and emitters. In this work, AlN/GaN superlattices with periodicities ranging from 10 to 20 Å have been grown via metal organic vapor phase epitaxy in order to investigate the influence of the interface on the binary alloy growth rates. The GaN growth rate at the interface was observed to decrease with increasing GaN thickness while the AlN growth rate remained constant. This has been attributed to a decrease in the decomposition rate of GaN at the hetero-interface as seen in other III-V hetero-structures.

The influence of N 2/H 2 and ammonia N source materials on optical and structural properties of AlN films grown by plasma enhanced atomic layer deposition

The influence of N 2/H 2 and ammonia as N source materials on the properties of AlN films grown by plasma enhanced atomic layer deposition using trimethylaluminum as metal source has been studied. The ϖ-2Θ grazing-incidence X-ray diffraction, high resolution transmission electron microscopy, and spectroscopic ellipsometry results on AlN films grown using either NH 3 or N 2/H 2 plasma revealed polycrystalline and wurtzite AlN layers. The AlN growth rate per cycle was decreased from 0.84 to 0.54 Å/cycle when the N source was changed from NH 3 to N 2/H 2. Growth rate of AlN remained constant within 100–200 °C for both N precursors, confirming the self-limiting growth mode in the ALD window. Al–Al bond was detected only near the surface in the AlN film grown with NH 3 plasma. AFM analysis showed that the RMS roughness values for AlN films grown on Si(100) substrates using NH 3 and N 2/H 2 plasma sources were 1.33 nm and 1.18 nm, respectively. The refractive indices of both AlN films are similar except for a slight difference in the optical band edge and position of optical phonon modes. The optical band edges of the grown AlN films are observed at 5.83 and 5.92 eV for ammonia and N 2/H 2 plasma, respectively. According to the FTIR data for both AlN films on sapphire substrates, the E 1(TO) phonon mode position shifted from 671 cm −1 to 675 cm −1 when the plasma source was changed from NH 3 to N 2/H 2.

High growth rate of AlN in a planetary MOVPE reactor

AlN growth in a low-scale production AIX2000HT MOVPE system was studied. The dependence of the growth rate on ammonia flow was shown to be of a threshold nature originating from gas-phase parasitic reactions. An AlN growth rate up to 8.6 μm/h under optimized reactor conditions was demonstrated.

Sequential growths of AlN and GaN layers on as-polished 6H–SiC(0001) substrates

Microstructures of surfaces and defects generated during initial and subsequent growths via metalorganic vapor-phase epitaxy of AlN(0001) films on 6H–SiC(0001) substrates and GaN(0001) films on AlN/SiC(0001) substrates have been investigated using atomic force microscopy and cross-sectional and plan-view transmission electron microscopy. Scratches present on the SiC surfaces did not appear to bias the nucleation of AlN. The lateral growth rate of AlN was greater than the vertical growth rate, leading to almost planar layers at 15 and 100 nm thicknesses. Partially coalesced islands were observed after nominally ∼15 nm of growth. Increasing the thickness to 100 nm resulted in complete island coalescence, formation of undulating films from the polishing scratches in the SiC substrate, a surface microstructure containing steps, terraces and small pits, and a reduced dislocation density relative to the 15 nm layers. The AlN/SiC interfaces contained steps and complex dislocation networks. GaN islands nucleated and grew on the AlN films. Complete coalescence of these islands occurred at thicknesses less than 100 nm. Dislocation density in the GaN films was reduced by increasing the thickness of either the AlN and or the GaN. Arguments are developed to account for these observations.

Influence of total pressure and precursors flow rates on the growth of aluminium nitride by high temperature chemical vapor deposition (HTCVD)

AbstractIn order to achieve AlN bulk growth, HTCVD chlorinated process is investigated. High growth rate and high crystalline quality are targeted for AlN films grown on (0001) 4H SiC at 1750 °C. The precursors used are ammonia NH3 and aluminium chlorides AlClx species formed in situ by action of Cl2 on high purity Al wire. Influence of total pressure, Cl2 flow rate and NH3 flow rate on AlN growth rate, crystalline state and microstructure are presented. Growth rates of up to 200 μm.h–1 have been reached for polycrystalline layers. Thermodynamic calculations were carried out and correlated to the experimental results. As‐grown AlN layers were characterized by SEM and X‐ray Diffraction. Surface morphology was studied by SEM and FEG‐SEM and crystallographic orientations were obtained by X‐ray diffraction on θ/2θ. (© 2009 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)