S. A. Safvi

Photoluminescence of erbium-implanted GaN and in situ-doped GaN:Er

The photoluminescence of in situ-doped GaN:Er during hydride vapor phase epitaxy was compared to an Er-implanted GaN sample. At 11 K, the main emission wavelength of the in situ-doped sample is shifted to shorter wavelengths by 2.5 nm and the lifetime is 2.1±0.1 ms as compared to 2.9±0.1 ms obtained for the implanted sample. The 295 K band edge luminescence of the in situ-doped sample was free of the broad band luminescence centered at 500 nm which dominated the spectrum of the implanted sample. Reversible changes in the emission intensity of the in situ-doped sample upon annealing in a N 2 versus a NH 3 / H 2 ambient indicate the probable role of hydrogen in determining the luminescence efficiency of these samples.

GaN Growth by Metallorganic Vapor Phase Epitaxy A Comparison of Modeling and Experimental Measurements

A model for the growth of gallium nitride in a vertical metallorganic vapor phase epitaxy (MOVPE) reactor is presented and compared to experimental growth rate measurements. For a mixture of nondilute gases, the flow, temperature, and concentration profiles are predicted using recent kinetic data. Growth rates are predicted based on simple reaction mechanisms and compared with those obtained experimentally. These comparative results show that the growth of GaN epi layers proceeds through an intermediate adduct of trimethylgallium and ammonia. Loss of adduct species due to oligmerization leads to the lowering of the growth rate. Quantification of this loss of reacting species is made based on experimentally observed growth rates. An apparent chemistry model is presented based on the salient features of GaN MOVPE. Process conditions are perturbed to obtain trends in growth rate and uniformity in order to demonstrate the utility of such a model in optimizing the GaN MOVPE process.

Effect of reactor geometry and growth parameters on the uniformity and material properties of GaNsapphire grown by hydride vapor-phase epitaxy

Abstract The effects of flow rate variation and geometry on the growth rate, growth uniformity and crystal quality were investigated in a horizontal gallium nitride vapor-phase epitaxy reactor. The effects of these parameters, were studied through the comparison of numerical model predictions to experimentally observed values. Gas-phase reactions between Groups III and V sources and deposition of material on the wall are shown to lead to reduced overall growth rates and may be responsible for inferior crystal quality. A low ammonia concentration is correlated with the deposition of polycrystalline films. A low V III ratio and ammonia concentration lead to inferior crystalline quality and increased yellow luminescence. An optimum HVPE growth process requires selection of reactor geometry and operating conditions to minimize gas-phase reactions and wall deposition while providing a uniform reactant distribution across the substrate.

Photoreflectance Study of the Long‐Term Stability of Various Surface Chemical Treatments on (001) n‐GaAs

A study of the long-term stability of etching, photowashing, and sulfide passivation [using (NH 4 ) 2 S] treatments performed on GaAs surfaces using photoreflectance spectroscopy is reported in this paper. Dramatic changes in the intensity of excitonic features of bulk n-GaAs qualitatively show much greater stability of sulfide-passivated than either etched or photowashed surfaces. We have also quantified the electric field in structures containing a thin, undoped GaAs layer over a highly doped n-GaAs buffer layer using strong Franz-Keldysh oscillations present in photoreflectance measurements. The results show a gradual degradation of the effects of etching and photowashing GaAs surfaces over a period of several months, while sulfide-passivated samples remain stable and, in some sense, unpinned over this same time period.

A Mass Spectroscopic Study of the Vapor Phase Thermal Decomposition of Trimethylamine

Trimethylamine has been used in the growth of compound semiconductors either through the formation of an adduct, as in trimethylamine allane, or as a possible growth reactant. The kinetics of the gas-phase decomposition and dominant reaction products relevant to these applications were determined in this study. The multistep thermal decomposition of trimethylamine in hydrogen (H 2 and D 2 ) in a laminar-flow tube reactor was studied by in situ mass spectroscopy and the analysis of isolated decomposition products. A dimethylamino radical and a methyl group are formed in a first-order Arrhenius-type decomposition that begins at ∼525 and is complete at ∼650°C. Additional products of this first step were deuterated methane, CH 3 D 2 (in D 2 ) and ethane, C 2 H 6 . The activation energy is 50.8 kcal/mol. In subsequent steps the dimethvlamino radical degrades through the series N-methylenemethylamine, (CH 3 )N = CH 2 , the imidoyl radical (CH 3 )N = C . H, and hydrogen cyanide, accompanied by loss of H 2 , hydrogen radical, and methyl radical, respectively, as well as by the formation of unidentified solids.

MOVPE GaN Gas-Phase Chemistry for Reactor Design and Optimization

The results of gas phase decomposition studies are used to construct a chemistry model which is compared to data obtained from an experimental MOVPE reactor. A flow tube reactor is used to study gas phase reactions between trimethylgallium (TMG) and ammonia at high temperatures, characteristic to the metalorganic vapor phase epitaxy (MOVPE) of GaN. Experiments were performed to determine the effect of the mixing of the Group III precursors and Group V precursors on the growth rate, growth uniformity and film properties. Growth rates are predicted for simple reaction mechanisms and compared to those obtained experimentally. Quantification of the loss of reacting species due to oligomerization is made based on experimentally observed growth rates. The model is used to obtain trends in growth rate and uniformity with the purpose of moving towards better operating conditions.

Effect of Growth Parameters and Local Gas-Phase Concentrations on the Uniformity and Material Properties of GaN/Sapphire Grown by Hydride Vapor-Phase Epitaxy

The effects of flowrate variation and geometry on the growth rate, growth uniformity and crystal quality were investigated in a horizontal Gallium Nitride vapor phase epitaxy reactor. To better understand the effects of these parameters, numerical model predictions are compared to experimentally observed values. Parasitic gas phase reactions between group III and group V sources and deposition of material on the wall are shown to lead to reduced overall growth rates and may be responsible for inferior crystal quality. A low ammonia concentration is correlated with the deposition of polycrystalline films. A low V/III ratio and an ammonia concentration lead to poor crystalline quality and increased yellow luminescence. An optimum HVPE growth process requires selection of reactor geometry and operating conditions to minimize these parasitic reactions and wall deposition while providing a uniform reactant distribution across the substrate.

A Modeling Study of GaN Growth by MOVPE

A model for the growth of gallium nitride in a vertical metalorganic vapor phase epitaxy reactor is presented. For a mixture of non-dilute gases, the flow temperature and concentration profiles are predicted. The results show that the growth of GaN epilayers is through an intermediate adduct of TMG and ammonia. Growth rates are predicted based on simple reaction mechanisms and compared with those obtained experimentally. Loss of adduct species due to polymerization leads to lowering in growth rate. An attempt to quantify loss of reacting species is made based on experimentally observed growth rates.