GaN Growth Rate Research Articles

Effects of thermal convection on growth rate of GaN by MOVPE

It was demonstrated that GaN growth rate by MOVPE depended on the reactor pressure, inclined angle of slanted susceptor, and the temperature gradient over substrate in the vertical direction, which were contributed to the thermal convection in gas-phase. The growth process was controlled by mass transported limited, that can be classified into the input rate limited and the diffusion limited, or their combination depending on the configuration of reactor and the experimental conditions.

In situ control of gan growth by molecular beam epitaxy

Methods to determine GaN surface temperature, surface composition, and growth rates using in situ desorption mass spectroseopy (DMS) and reflection high energy electron diffraction (RHEED) are demonstrated for molecular beam epitaxial growth of GaN using NH3. Using these methods, the GaN surface temperature, Ts, and GaN growth rates as a function of Ts, Ga flux, and NH3 flux were obtained. Surface temperatures were determined from DMS and RHEED measurements of the temperature at which Ga condenses on GaN. NH3-limited and Ga-limited growth regimes are identified and the transition between these regimes is shown to be abrupt. NH3-limited samples have a weakly reconstructed (2 × 2) RHEED pattern, while Ga-limited samples reveal a transmission pattern. Atomic force microscopy showed that NH3-limited samples exhibit atomic steps while Ga-limited samples exhibit faceting.

Heteroepitaxial growth of InN on Si(111) using a GaAs intermediate layer

Thermal nitridation of GaAs(111) in flowing NH 3 and MOCVD growth of InN on the nitrided GaAs(111) have been studied. A GaN layer with a smooth surface and a uniform thickness is formed on GaAs(111) as a result of the thermal nitridation. The growth rate of GaN on GaAs(111) is considerably larger than that on GaAs(100) surface. The crystalline structure of GaN layer is dependent on nitridation temperature; a cubic lattice for GaN formed at a relatively low temperature (∼ 600°C) and a hexagonal lattice at a high temperature (∼900°C). A hexagonal InN layer with an excellent surface morphology is heteroepitaxially grown on nitrided bulk GaAs(111). Using a thin (∼0.5 μm) GaAs(111) layer on Si(111), an InN/GaN/Si structure is obtained by adjusting nitridation temperature for GaAs(111) layer. Through these investigations, it has been demonstrated for the first time that a nitrided bulk GaAs(111) can be used as a substrate for InN growth and, furthermore, a nitrided GaAs(111) layer on Si(111) can be employed as an intermediate layer for the heteroepitaxial growth of InN on Si.

Single Crystal Gallium Nitride on Silicon Using SiC as an Intermediate Layer

AbstractGaN films have been grown atop SiC intermediate layers on Si(001) and Si(111) substrates using supersonic jet epitaxy (SJE). GaN growth temperatures ranged between 600 °C and 775 °C. Methylsilane (H3SiCH3) was used as the single source precursor for SiC growth and triethylgallium (TEG) and ammonia (NH 3) were the sources for GaN epitaxy. The GaN growth rate was found to depend strongly on substrate orientation, growth temperature, and flux. Structural characterization of the films was done by transmission electron diffraction (TED) and x-ray diffraction (XRD). Growth of GaN on SiC(002) produces a cubic or mixed phase of cubic and wurtzite depending on growth conditions. Growth on SiC(111) produces predominantly wurtzite GaN(0002). Minimum rocking curve widths for GaN(0002) on SiC/Si(111) and GaN(002) on SiC/Si(001) are 0.6° and 1.5°, respectively. Cross Sectional Transmission Electron Microscopy (XTEM) was also performed.

Homoepitaxial Growth of GaN Using Seeded Supersonic Molecular Beams

AbstractHomoepitaxial growth of GaN on MOCVD-grown GaN/AlN/6H-SiC substrates was investigated using NH3-seeded supersonic molecular beams and an effusive Ga source. Ga-limited growth is observed at 730 and 770°C for incident Ga fluxes ≤ 1.2×1015 cm−2 s−1 using a 0.25 eV NH3 beam. A Ga incorporation efficiency of 20–25% is observed under these conditions. Increasing NH3 kinetic energy in the 0.25 to 0.61 eV range results in a modest increase in the GaN growth rate which we ascribe to an enhancement in NH3 reactivity. A concomitant increase in surface roughness is observed with increasing GaN growth rate.

High temperature adduct formation of trimethylgallium and ammonia

High temperature gas phase reactions between trimethylgallium (TMG) and ammonia were studied by means of in situ mass spectroscopy in an isothermal flow tube reactor. The temperature, pressure, and reaction time were chosen to emulate the gas phase environment typical of the metal–organic vapor phase epitaxy (MOVPE) of GaN. The main gas phase species is [(CH 3)2Ga:NH2]x, where most probably x=3, resulting from the very fast adduct formation followed by elimination of methane. The further gas phase decomposition of this species proceeds through the stepwise elimination of methane. These studies indicate that little TMG exists within the growth ambient under most MOVPE growth conditions. The further gas phase reaction of [(CH3)2Ga:NH 2]x may be responsible for the strong dependence of the MOVPE GaN growth rate and uniformity commonly observed.

Growth of GaN on sapphire (0001) using a supersonic jet of plasma-generated atomic nitrogen

We describe a new GaN film growth method employing a supersonic jet of nitrogen atoms and a gallium effusion cell. The nitrogen atoms were generated by exciting a 1% nitrogen in helium mixture with a radio frequency discharge. X-ray diffraction and in situ reflection high-energy electron diffraction indicate that GaN films grown on sapphire (0001) were single crystalline and epitaxial with a rough surface morphology. A GaN growth rate of approximately 0.65 μm/h was measured, independent of substrate temperature over the range of 600–750 °C. However, the crystalline quality of the film increases markedly with increasing wafer temperature.

GaN Film Growth by a Supersonic Arcjet Plasma

AbstractThis paper reports on preliminary studies of GaN growth obtained using a supersonic nitrogen arcjet plasma expanding into low pressure. A hydrogen-free and carbon-free growth environment was achieved by use of a Ga vapor source positioned downstream of the expanding plume. GaN growth rates of around 8 μm/hour were obtained in these preliminary studies. We believe these growth rates are the highest reported for a non-chemical decomposition process. The growth rates are attributed to the very high nitrogen atom fluxes estimated to be on the order of 1019 atoms/cm2/sec. The initial growth rates are believed to be well below those possible with a fully optimized system. The GaN films are characterized by Raman spectroscopy, visible-IR transmission, and x-ray diffraction. The deposited films appear to be single crystal and epitaxial on basal plane sapphire substrates.

Material and Device Characteristics of MBE-Grown GaN Using a New rf Plasma Source

ABSTRACTA new rf plasma nitrogen source has been characterized for growth of GaN on basal-plane sapphire by molecular beam epitaxy. For rf power of 500 W and N2 flow rate of 2 sccm, a maximum GaN growth rate of 0.80 μm/hr is obtained, implying a source efficiency greater than 5%. It is found that the GaN surface roughness is extremely sensitive to V:Il ratio near unity and independent of growth rate in the range 0.3-0.8 μm/hr. Roughness as small as 1.0 nm (rms) is measured by atomic-force microscopy. Microstructure of the high-growth-rate films is similar to other GaN films, as observed in cross-section transmission electron microscope images. The electroluminescence spectra from homojunction light-emitting diodes exhibit a band of nearultraviolet emissions corresponding to the energy separation of the intentional donor and acceptor levels on the two sides of the junction. The intensity of these emissions relative to the visible spectrum increases with drive current density, implying saturation of deep trap levels responsible for the visible light output.

GaN grown by molecular beam epitaxy at high growth rates using ammonia as the nitrogen source

The 9.5 eV bond energy of the nitrogen molecule makes it very difficult to break it up into atoms and incorporate in III–V nitride compounds grown by molecular beam epitaxy (MBE). By comparison, it is relatively easy to dissociate ammonia due to the existence of a catalytic effect on the GaN surface when there is Ga present. Using ammonia as the nitrogen source, we have achieved high quality GaN by MBE at a growth rate as high as 1 μm/h. This is an order-of-magnitude faster than previously reported using electron-cyclotron resonance plasma-assisted growth. Most importantly, our results indicate that there is no intrinsic limit to the growth rate of GaN using ammonia, a situation similar to that of conventional III–V MBE using gas sources. The unintentional n-type doping as low as 2×1017 cm−3 at room temperature. In addition, room-temperature hole densities of 4×1017 cm−3 in Mg-doped GaN films have been achieved without postgrowth annealing. Low-temperature photoluminescence for both undoped and Mg-doped GaN are dominated by near band-edge emissions without deep-level related luminescence, indicative of high quality materials.

Plasma-assisted low-pressure metalorganic chemical vapor deposition of GaN on GaAs substrates

Cubic and hexagonal GaN films were grown on (001) GaAs substrates by plasma-assisted low-pressure metalorganic chemical vapor deposition using triethylgallium and nitrogen radicals. The GaN growth rate was lower than that of GaAs and it was enhanced by simultaneous supply of hydrogen radicals to the growing surface. Cubic GaN was grown epitaxially under Ga-rich conditions, and c-axis oriented hexagonal GaN was grown under N-rich conditions.

Surface orientation dependence of growth rate of cubic GaN

The metalorganic vapor phase epitaxy (MOVPE) growth of cubic GaN has been performed on the patterned GaAs(100) substrates which have (111)A or (111)B facets. It is found that the growth features are strongly dependent on the configuration of the pattern. It is deduced that these features come from the surface-orientation-dependent growth rate, which is in the order (111)B > (100) > (111)A, combined with the diffusion of Ga adatoms on the surface. Taking advantage of the growth on the patterned substrates, the diffusion length of the Ga adatoms on the GaAs(100) surface is estimated to be several microns in the typical case.

Plasma Potential Measurements and Strain Effects in Epitaxial GAN Grown on AlN Buffered Si(111) by Radio Frequency Reactive Sputtering

AbstractWe have grown epitaxial GaN thin films on A1N buffered Si(lll) by radio frequency glow discharge sputtering. GaN growth direction strains and GaN E2 optical phonon energies are measured. At the same growth temperature, plasma potentials of the radio frequency glow discharge in which GaN is grown, GaN growth rate, and strain in GaN increase systematically as a function of increasing input power. The measured GaN E2 optical phonon energy scales with GaN lattice strain. Our results indicate the presence of significant intrinsic stresses in epitaxial GaN films and point to the importance of plasma characteristics in controlling the physical properties during plasma assisted thin film deposition.

MOCVD of GaN Using Diethylgalliumazide and Ammonia

ABSTRACTGaN thin films have been deposited on Si and sapphire substrates by metalorganic chemical vapor deposition (MOCVD) using diethylgalliumazide and ammonia. Films were grown in the temperature range of 500-750°C. Growth rates were monitored in situ using laser interferometry. The addition of ammonia enhanced the growth rate significantly. At high temperatures, gas-phase depletion of the precursor reduced the growth rate of GaN. Films grown on (0001)-oriented sapphire substrates at temperatures above 650°C were highly textured with smooth surface morphology. Optical and electrical properties of the films are discussed and compared to those of films grown using conventional Ga and N sources.

Kinetics of the epitaxial growth of GaN using Ga, HCl and NH 3

This paper deals with the effects of the growth parameters, the position of the substrate, the reactant gas flow rate and the substrate temperature, upon the epitaxial growth rate of GaN on (0001) sapphire substrates. The growth technique used was the chemical vapor deposition method utilizing Ga, HCl and NH 3. The crystal growth rate in the presence of excess NH 3 increases linearly with the quantity of Ga transported from the source zone, whereas it decreases exponentially with the distance from the inlet nozzle end. The activation energy for the GaN formation is estimated to be about 1.1 eV (25 kcal/mol), and this energy is interpreted as that for the surface reaction step. These results are discussed from a simple chemical kinetics standpoint.