To Trimethylgallium Research Articles

Gallium Nitride Growth Using Diethylgallium Chloride as an Alternative Gallium Source

Metal organic vapor phase epitaxy (MOVPE) of GaN has been carried out using diethyl gallium chloride (DEGaCl) and ammonia. The growth rate and efficiency of the DEGaCl-based growth decreases with increasing temperature when compared to trimethyl gallium (TMG)-based growth under similar conditions. Both low temperature buffer and the high temperature GaN layers were grown using the DEGaCl-NH3 precursor combination on the basal plane of sapphire and compared to similar structures grown using TMG and NH3. DEGaCl-based growth reveals an improved growth behavior under identical growth conditions to the conventional TMGa and ammonia growth. X-ray, Hall, and atomic force microscopy (AFM) measurements have been carried out on these samples providing a direct comparison of materials properties associated with these growth precursors. For the DEGaCl-based growth, the x-ray rocking curve line width, using the (0002) reflection, is as low as 300 arcsec on a 2.5-micron thick film. A RMS surface roughness of ∼0.5nm measured over a 10×10 micron area.

Growth and characterization of GaN films on (0001) sapphire substrates by alternate supply of trimethylgallium and NH 3

GaN films were grown on (0001) sapphire substrates in a temperature range of 500∼950°C by exposing the substrates to trimethylgallium (TMG) and NH 3 one at a time. High quality GaN films were achieved at 800∼900°C with a thin GaN buffer layer predeposited at 500°C. The linewidth of the (0004) double-crystal rocking curve X-ray diffraction (DCXRD) of a 2.0 μm thick GaN film is about 250∼500 arcsec. Increment in growth temperature over a temperature range of 800∼900°C is helpful to suppress the intensity of yellow luminescence and to enhance the luminescence intensity of the near band-to-band emission. Typically, the room temperature photoluminescence intensity ratio of the near band edge emission to the yellow luminescence for an as-grown high quality GaN film is more than one order of magnitude. The best GaN films with superior optical behavior were achieved at ∼900°C with a V/III ratio of 5000. Photoluminescence measurements of these GaN films at 9 K show strong and sharp near band-to-band emission with almost no yellow luminescence.

Gallium Nitride Growth Using Diethylgallium Chloride as an Alternative Gallium Source

AbstractMetal organic vapor phase epitaxy (MOVPE) of GaN has been carried out using diethyl gallium chloride (DEGaCI) and ammonia. The growth rate and efficiency of the DEGaCl-based growth decreases with increasing temperature when compared to trimethyl gallium (TMG)-based growth under similar conditions. Both low temperature buffer and the high temperature GaN layers were grown using the DEGaCI-NH3 precursor combination on the basal plane of sapphire and compared to similar structures grown using TMG and NH3. DEGaCl-based growth reveals an improved growth behavior under identical growth conditions to the conventional TMGa and ammonia growth. X-ray, Hall, and atomic force microscopy (AFM) measurements have been carried out on these samples providing a direct comparison of materials properties associated with these growth precursors. For the DEGaCl-based growth, the x-ray rocking curve line width, using the (0002) reflection, is as low as 300 arcsec on a 2.5-micron thick film. A RMS surface roughness of ∼0.5nm measured over a 10x10 micron area.

Kinetics and mechanism of atomic layer epitaxy of GaAs using trimethylgallium

The desorption time constant of carbon-related species from clean GaAs surfaces exposed to trimethylgallium (TMGa), measured by in situ Auger electron spectroscopy, is of the order of 100 s in the temperature range where atomic layer epitaxy of GaAs takes place. A set of rate equations based on the adsorbate-inhibition model using this desorption time constant is shown to reproduce atomic layer epitaxy growth results: the GaAs growth rate dependence on the TMGa supply duration and the growth rate of the double TMGa pulse experiments with purge time in between two TMGa pulses. The origin of the remaining discrepancies is discussed.

Adsorption of carbon-related species onto GaAs(001), (011), and (111) surfaces exposed to trimethylgallium

The adsorption/desorption process of carbon-related species on GaAs surfaces exposed to trimethylgallium (TMGa) was studied using in situ Auger electron spectroscopy (AES) and reflection high-energy electron diffraction (RHEED) as a function of the various surface reconstructions and orientations. The adsorption of C originating from TMGa and its transient behavior were observed on Ga-stabilized (001)-4×6 and (111)B-√19×√19 surfaces. On the other hand, the C KLL (273 eV) signal intensity on (011) and (111)A surfaces was extremely low, even just after exposure to TMGa. The growth rates of GaAs grown by chemical beam epitaxy using an alternating supply of TMGa and arsine depended strongly on the substrate orientations, corresponding to the adsorption of the C-containing species on the surfaces. The results indicated that the self-limiting monolayer growth (atomic-layer epitaxy) of GaAs is caused by the adsorbed alkyls, which terminate surfaces and block all of the decomposition sites for TMGa.

Adjusting trimethylgallium injection time to explore atomic layer epitaxy of GaAs between 425 and 500°C by organometallic vapor phase epitaxy

In experiments employing a conventional low-pressure, rotating-disk organome-tallic vapor phase epitaxy reactor, GaAs epilayers have been grown at substrate temperatures ranging from 425 to 500°C by exposing the substrate alternately to trimethylgallium (TMG) and AsH3.The GaAs growth rateR was approximately constant with TMG flow rate, but with increasing TMG injection timet, it increased to more than one monolayer per TMG/AsH3 cycle without saturating. Although growth was not self-limiting, for one specific combination of temperature andt, a value of R = 1 monolayer/cycle could be achieved by usingt values decreasing from 10.8 s at 425°C to 0.9 s at 500°C in accordance with an Arrhenius relationship between 1/t and absolute temperature.

In situ Auger electron spectroscopy of carbon transient behavior on GaAs surfaces exposed to trimethylgallium

Surface species and its transient behavior on GaAs surfaces exposed to trimethylgallium (TMGa) have been observed directly by in situ Auger electron spectroscopy under the condition where the self-limiting growth of GaAs takes place by chemical beam epitaxy (CBE). After exposure to TMGa, the initial carbon (C) intensity related to alkyls originating from TMGa exponentially decreases with a large time constant (105 s, at 490°C), eventually reaching a steady state. The dynamic transient of surface reconstruction during this desorption process of the alkyls was observed by reflection high-energy electron diffraction. A modified atomic layer epitaxy growth showed that self-limiting growth occurs on the steady state surface.

Hall effect analysis of high purity p-type GaAs grown by metalorganic chemical vapor deposition

Variable temperature Hall effect and low temperature photoluminescence measurements have been performed on high purityp- andn-type GaAs grown at atmospheric pressure by metalorganic chemical vapor deposition. These high purity epitaxial GaAs layers were grown as a function of the arsine (AsH3) to trimethylgallium (TMG) ratio (V/III ratio). The accurate quantitative assessment of the electronic properties of thep-type layers was emphasized. Analysis of the material focussed on the variation of the concentration of the shallow impurities for different V/III ratios. Surface and interface depletion effects are included to accurately estimate the concentration of impurities. The model of the merging of the excited states of the acceptor with the valence band is used to include the dependence the activation energy of the impurity on the acceptor concentration as well as on acceptor species identity. The characteristicp- ton-type conversion with increasing V/III ratio was observed in these samples and the reason for thep- ton-type conversion is that the background acceptor concentration of carbon decreases and the germanium donor concentration increases as the V/III ratio is increased.

Direct writing of GaAs monolayers by laser-assisted atomic layer epitaxy

Direct writing of GaAs epitaxial monolayers has been achieved by laser-assisted atomic layer epitaxy (LALE) technique on GaAs substrates. Sequential exposures of the substrate to trimethylgallium (TMG) and arsine (AsH3) were separated by periods of hydrogen purging to prevent mixing. Laser beam scanning of the samples took place either during the flow of TMG or AsH3. The selectively grown films at the one monolayer per cycle condition have a mirrorlike surface and a flat top thickness profile. LALE has been realized at temperatures as low as 300 °C and over a wide range of TMG flux and laser power densities. Photoluminescence results of the deposited films show that their quality are comparable to those achieved by conventional ALE.

The role of CH 4 in metal organic chemical vapour deposition of GaAs

A study of the growth of GaAs in the metal organic chemical vapour deposition system over a wide range of temperatures (743–1023 K) and AsH 3 to trimethylgallium (TMG) pressure ratios (6–40) shows that the process is not affected by the addition of CH 4 to the gas phase. This holds true not only for the rate of deposition but also for the morphology of the films and their electrical and photoluminescence characteristics. It is argued that this result is a direct consequence of the stability of the CH 4 molecule. The incorporation of carbon during film growth most likely takes place via adsorbed CH 3 radicals, and their decomposition products, arising from the dissociation of TMG.