GaN Growth Rate Research Articles

The effect of HVPE reactor geometry on GaN growth rate—experiments versus simulations

In the study, presented in this paper, the growth of GaN layers by Hydride vapour phase epitaxy was investigated both experimentally and numerically. Modelling the flows in the reactor, combined with basic chemistry, gives a good approximation to the actual growth experiments. It was found that small changes in the reactor geometry, e.g.the inlet of GaCl, have a large effect on the growth rate as well as on the uniformity of the growth.

Growth of bulk GaN on GaN/sapphire templates by a high N2 pressure method

AbstractThe results of high‐pressure directional growth of GaN on GaN/sapphire templates are presented. The GaN growth rate as a function of the temperature gradient and time is determined. Changes of the growth rate with time are explained. The results of the crystallization process are briefly compared with those obtained for directional growth on pressure‐grown GaN crystals. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Surface chemistry and transport effects in GaN hydride vapor phase epitaxy

A simple quasi-thermodynamic model of surface chemistry in GaN hydride vapor phase epitaxy (HVPE) is presented. The model is coupled with the detailed 3D simulations of species transport in a horizontal-tube reactor and validated by the comparison with the data on the GaN growth rate obtained by laser reflectometry. Parametric study of the growth rate as a function of temperature and species flow rates has been performed over a wide range of growth conditions. The important role of species transport in an HVPE reactor is demonstrated. In particular, a strong effect of the natural concentration convection resulting in the formation of recirculation zones and in a non-uniform vapor composition is revealed by modeling. The impact of these effects on the GaN growth rate and V/III ratio on the growth surface is discussed in detail.

Nitride-Based LEDs With 800<tex>$^circhboxC$</tex>Grown p-AlInGaN–GaN Double-Cap Layers

GaN-based light-emitting diodes (LEDs) with various p-cap layers were prepared. It was found that surface morphologies of the LEDs with 800/spl deg/C grown cap layers were rough due to the low lateral growth rate of GaN. It was also found that 20-mA forward voltage of the LED with 800/spl deg/C grown p-AlInGaN-GaN double-cap layer was only 3.05 V. Furthermore, it was found that we could achieve a high output power and a long lifetime by using the 800/spl deg/C grown p-AlInGaN-GaN double-cap layer.

GaN quantum dot density control by rf-plasma molecular beam epitaxy

We report on the growth of GaN quantum dots and the control of their density in the Stranski–Krastanov mode on AlN (0001) by rf-plasma molecular beam epitaxy at 750 °C. After depositing the equivalent of 2–3 ML GaN coverage, as limited by N fluence under Ga-droplet growth conditions, excess Ga was desorbed and Stranski–Krastanov islands formed under vacuum. We present the dependence of island density as a function of GaN coverage (for two growth rates: 0.10 and 0.23 ML/s), as estimated from atomic force microscopy and cross-sectional transmission electron microscopy. With a GaN growth rate of 0.23 ML/s, the island density was found to vary from less than 3.0×108–9.2×1010 cm−2 as the GaN coverage was varied from 2.2 (critical thickness) to 3.0 ML. For a GaN growth rate of 0.10 ML/s, the island density varied from 2.0×1010 to 7.0×1010 cm−2 over a GaN coverage range of 2.0–3.0 ML. For each growth rate, the GaN islands were found to be of nearly uniform size, independent of the quantum dot density.

Systematic study of effects of growth conditions on the (nano-, meso-, micro)size and (one-, two-, three-dimensional) shape of GaN single crystals grown by a direct reaction of Ga with ammonia

A series of experiments have been conducted to systematically study the effects of growth conditions (NH3 flow rate, growth temperature, chamber pressure, and growth location) on the size (nano, meso, or micro) and the shape (one, two, or three dimensional) of GaN single crystal products grown by a direct reaction of Ga with NH3. A growth map with a wider range of experimental parameters was developed; it has three distinct zones. The size and shape of the products in every zone were found to depend on both temperature and NH3 flow rate with other growth conditions fixed. An effective surface diffusion length consisting of the Ga atomic surface diffusion length and the GaN molecular surface diffusion length, and the anisotropy of the Ga surface diffusion length and the GaN growth rate in different growth directions were introduced into the growth model, in such a way that it allowed successful explanation of all observed results. The optimal growth parameters could thus be determined, which conclusively demonstrated that nanowires with uniform diameter, clear crystal structure, length larger than 1 mm, uniform location distribution, and high yield can be obtained. Such a growth map based on in-depth understanding of the growth mechanism provides a clear direction for growing various materials with desired size and shape.

Deposition behavior of GaN in AIX 200/4 RF-S horizontal reactor

In this paper, we report on a combined modeling and experimental analysis of the GaN deposition behavior in the horizontal AIX 200/4 RF-S reactor. The study was aimed at revealing the effect of the variations of the operating parameters on the growth rate and uniformity. Variations of the trimethylgallium and hydride flow rates, changes in the composition of the mixture supplied through the hydride inlet, and the total flow redistribution between two reactor inlets have been considered. To get an insight into the mechanisms governing the measured GaN growth rate alterations, a detailed three-dimensional modeling has been used. Application of the reactor model accounting for important features of the reactor design and utilizing advanced chemical models has allowed us to reproduce fairly well experimental data and to draw conclusions on the mechanisms governing the deposition process.

Temperature influence on the growth of gallium nitride by HVPE in a mixed H 2/N 2 carrier gas

The growth of GaN by HVPE has been analysed by means of a thermodynamical and kinetic study. Two mechanisms involved in the growth of (00.1) GaN HVPE have been deduced from the numerous experiments performed on (0 0 1) GaAs by the chloride method. The parameters of these two growth mechanisms have been resolved from the experimental variations of HVPE GaN growth rate. Experiments performed in conditions of expected fast etching by HCl, in a mixed H 2/N 2 carrier gas, led to a new growth mechanism by considering a combined Cl desorption by GaCl as GaCl 2 and an etching by HCl. The apparent activation energy of the new Cl desorption reaction is the only new parameter introduced in the third growth mechanism. In this paper, we present the results obtained for the determination of a more accurate value of this new parameter. The growth rate was measured versus the growth temperature for different H 2 concentrations in the carrier gas. A quite good agreement was obtained between experimental and theoretical values.

The growth mechanism of GaN grown by hydride vapor phase epitaxy in N 2 and H 2 carrier gas

This paper investigates the growth mechanism of GaN for the hydride vapor phase epitaxy (HVPE) process in the N 2 and H 2 carrier gas ambients. Differences are observed between the surface morphologies of GaN films grown in N 2 carrier gas and those grown in H 2 carrier gas. It is determined that the GaN growth direction and growth rate are both affected by H 2 flow rate. In N 2 ambient, the {1 1 ̄ 0 1} facet is stable, because of the N-polarity and high dangling bond density (DB) of {1 1 ̄ 0 1} facet. On the other hand, in H 2 ambient, and the {1 1 ̄ 0 0} facet becomes stable. In this paper, this phenomenon will be explained by the atomic configuration model of the GaN wurtzite structure.

In-Situ Monitoring of GaN Growth by Hydride Vapor Phase Epitaxy

In-situ reflectivity measurements of the growth surface during deposition in a Hydride Vapor Phase Epitaxy system are presented. The GaN growth rate increases linearly with the HCl flow and increases monotonically with the ammonia flow. Following the replacement of the carrier gas nitrogen by hydrogen, the growth rate initially increases, passes through a maximum at a H-2 concentration of 0.15 and then decreases.

Surface polarity dependence of decomposition and growth of GaN studied using in situ gravimetric monitoring

The influence of lattice polarity of wurzite GaN(0 0 0 1) on its decomposition rate was investigated using an in situ gravimetric monitoring (GM) method with freestanding GaN(0 0 0 1) substrates. At temperatures between 800°C and 850°C, the decomposition rate of GaN(0 0 0 1) was faster than that of GaN( 0 0 0 1 ̄ ). On the other hand, the decomposition rate of GaN( 0 0 0 1 ̄ ) was faster than that of GaN(0 0 0 1) at temperatures between 900°C and 950°C. The relation between the decomposition rate and the H 2 partial pressure ( P H 2 ) indicates that the rate-limiting reactions are N(surface)+ 3 2 H 2(g)→NH 3(g) at lower temperatures, but Ga(surface)+ 1 2 H 2(g)→GaH(g) at higher temperatures. In addition, we used the GM method to measure the growth rate of GaN(0 0 0 1) on freestanding GaN(0 0 0 1) substrates. In the low-temperature region, GaN( 0 0 0 1 ̄ ) grew faster than GaN(0 0 0 1), whereas GaN(0 0 0 1) grew faster than GaN( 0 0 0 1 ̄ ) in the high-temperature region.

Influence of MOVPE growth conditions on carbon and silicon concentrations in GaN

Impurity incorporation is studied as a function of metalorganic vapor phase epitaxy growth conditions. The same GaN growth conditions were used initially, resulting in films with approximately the same dislocation density, after which a single growth parameter was varied and the impurity concentrations measured using SIMS. The C concentrations were found to decrease with increasing growth temperature, pressure, and ammonia flow, and to increase with increasing H 2 carrier and trimethylgallium flow. The Si concentrations for both unintentionally doped (UID) and intentionally doped (ID) films increased with increasing growth pressure. The UID and ID Si concentrations varied inversely with the GaN growth rate, suggesting an independent source for UID Si within the reactor. Moreover, the NH 3 flow rate influenced the Si-doping concentration, even though the GaN growth rate remained constant. A H 2/NH 3 etching mechanism is proposed to explain the growth parameter influence on the observed C and Si concentrations. The reduction in the ID Si concentrations at high NH 3 flows is explained by NH 3 site blocking, similar to that proposed for increased Ga vacancies at high NH 3 flows.

Transport and Chemical Mechanisms in GaN Hydride Vapor Phase Epitaxy

ABSTRACTOn the basis of both experimental and theoretical studies, a simple quasi-thermodynamic model of surface kinetics is suggested for Hydride Vapor Phase Epitaxy (HVPE) of GaN, working in a wide range of growth conditions. Coupled with detailed 3D modeling of species transport in a horizontal reactor, the model provides quantitative predictions for the GaN growth rate as a function of process parameters. Significance of transport effects on growth rate uniformity is demonstrated.

Growth of GaN and related materials by gas-source molecular-beam epitaxy using uncracked ammonia gas

High-quality GaN and related materials were grown using gas-source molecular-beam epitaxy (GSMBE). The cracking species of an ammonia gas was investigated using a quadruple mass spectrometer. Ammonia gas without cracking was used for the growth and was effectively grown on the substrate surface above 800°C. An undoped GaN layer (1 mm-thick) with a smooth surface was grown on a GaN buffer layer at 850°C. A higher growth rate of GaN was obtained (1.5 μm/h). This is the highest growth rate of the GSMBE using uncracked ammonia gas. The mobility of undoped GaN was 350 cm 2/V s and the carrier concentration was 6×10 16 cm 3 at room temperature. An Al 0.2Ga 0.8N/GaN heterostructure was also grown on a sapphire substrate. The mobility of the AlGaN/GaN heterostructure was 1230 cm 2/V s at room temperature. An Al 0.2Ga 0.8N/GaN hetero field effect transistor (HFET) was fabricated. A good electrical property of HFET with a high breakdown voltage was realized.

Kinetics and gas-surface dynamics of GaN homoepitaxial growth using NH 3-seeded supersonic molecular beams

The kinetics of homoepitaxial growth of GaN thin films on metal-organic chemical vapor deposition (MOCVD)-grown GaN(0 0 0 1)/AlN/6H-SiC substrates was probed using NH 3-seeded supersonic molecular beams. NH 3 was seeded in H 2 and He and antiseeded in N 2 and Ar in order to obtain incident kinetic energies of 0.08–1.8 eV. Nozzle temperatures of 35–600 °C were used to adjust the NH 3 internal energy. Intense NH 3 beams (fluxes >2×10 15 cm −2 s −1 at the substrate) are produced for low seeding percentages (<5%) in the lighter carrier gases, because the heavier species (NH 3) is focused along the centerline of the beam. The NH 3 flux is proportional to the ratio of its molecular weight to the average molecular weight of the binary gas mixture. A steady-state Langmuir–Hinshelwood kinetics model was used to extract zero-coverage NH 3 sticking coefficient ( α NH 3 0) values from GaN growth kinetics data. An α NH 3 0 value of 0.14 at 750 °C was determined using seeded supersonic beams of NH 3 in He with incident kinetic energies of 0.4–0.5 eV. In comparison, GaN growth rates using low-energy NH 3 molecules (0.03 eV) from a leak valve indicate an α NH 3 0 of 0.29. Growth rate measurements using NH 3 beams with kinetic energies of 0.08–1.8 eV confirmed that α NH 3 0 generally decreases with increasing incident kinetic energy, leading us to conclude that NH 3 chemisorption on GaN(0 0 0 1) is unactivated and occurs via a precursor-mediated mechanism. Internal energy enhancement of NH 3 chemisorption via a precursor-mediated channel is proposed to explain the effects of nozzle temperature on GaN growth kinetics. The effects of NH 3 incident kinetic energy on film morphology are indirect. Rough, highly faceted films are observed under Ga-limited growth conditions. The surface morphology of films grown under NH 3-limited conditions changes from rough to smooth as the effective V/III ratio is decreased.

Hydrogen and nitrogen ambient effects on epitaxial growth of GaN by hydride vapour phase epitaxy

This study presents the influence of the composition of the carrier gas on the growth of GaN by HVPE. Since no hydrogen is introduced in the vapour phase, the deposition is expected to be controlled by Cl desorption in the form of GaCl 3, as has been proposed for GaAs. However, our published model predicts much lower growth rates than those observed. We can account for both the observed parasitic deposition and GaN growth rate if we assume that GaCl 3 is not at its equilibrium pressure in the deposition zone and where nucleation takes place on the walls as well as on the substrate. This yields a high rate of parasitic nucleation even though the nominal supersaturation is vanishing small. Very little growth takes place on the substrate where the equilibrium pressure of GaCl 3 is reached. We describe similar experiments performed with a H 2/N 2 mixture as the carrier gas. In this case, we expect GaN deposition to be controlled by desorption of Cl as HCl, which is known as the H 2 mechanism. It is speculated that the results show the existence of a new growth mechanism.

The influence of Si-doping to the growth rate and yellow luminescence of GaN grown by MOCVD

The growth of Si-doped GaN films was performed by MOCVD using a homemade reactor operating at atmospheric pressure on (0 0 0 1) oriented sapphire. A study of the effect of Si-doping indicated that the intensity of yellow band emission in GaN : Si films decreased with the increasing of SiH 4/TMGa ratio, and it was largely influenced by the parasitic reactions in the gas phase. The yellow band intensity was depressed when the parasitic reactions were reduced. We also observed that the growth rate of GaN : Si films was influenced by the Si doping and the parasitic reactions. The growth rate decreased with the increase of SiH 4/TMGa ratio and was larger in larger parasitic reactions reactor. Si-doped GaN films with carrier concentration of 2×10 19 cm −3, electron mobility of 120 cm 2/V s, FWHM of the band-edge emission of only 60 meV at room temperature, and no yellow emission were obtained.

In situ determination of growth rate by pyrometric interferometry during molecular-beam epitaxy: Application to the growth of AlGaN/GaN quantum wells

In this article, we report on the application of pyrometric interferometry to monitor the growth rate of (Al)GaN in situ during molecular-beam epitaxy. Since the growth rate of III-nitrides is very sensitive to the nitrogen flux, it is important to monitor the variation in growth rate from run to run. Using this method, we grew GaN/AlxGa1−xN quantum-well structures with well thicknesses between 10 and 40 Å. The thicknesses of the quantum wells were confirmed by cross-sectional transmission electron microscopy measurements and found to be in good agreement with the corresponding growth rate determined in situ during the growth process.

Incorporation of Mg in GaN grown by plasma-assisted molecular beam epitaxy

We describe dramatically decreased Mg incorporation in GaN above a critical Mg flux. Secondary ion mass spectroscopy analysis showed a linear increase in Mg concentration up to a flux equivalent to 8.0×10−10 Torr beam equivalent pressure (BEP) and 1.6×10−9 Torr BEP at 550 and 615 °C respectively, beyond which the Mg incorporation was reduced by factors of 10 for 550 °C, and 2 for 615 °C. In a transition region between this critical flux and higher flux, a time dependent incorporation phenomenon was observed. An increase in the GaN growth rate was also observed in the presence of Mg above the critical flux.

The dependence of GaN growth rate on electron temperature in an ECR plasma

Experiments on the deposition of GaN thin films were carried out in an ECR plasma reactor using nitrogen gas and trimethylgallium (TMG) as precursors. Electron temperature and nitrogen species adjacent to the substrate surface during deposition were measured by a CCD spectrometer. We observed an optimum electron temperature for the growth rate. The result suggests that tuning of electron energy (or temperature) can be used to optimize the deposition and electron temperature near the substrate surface may be a candidate for one of the control parameters in plasma-assisted CVD.