Growth of bulk InGaN films and quantum wells by atmospheric pressure metalorganic chemical vapour deposition

InGaN bulk layers and single quantum wells were grown on 1.4 to 2.4 μm thick GaN on sapphire films by atmospheric pressure metalorganic chemical vapour deposition (AP-MOCVD). The morphology of the epitaxial layers was strongly affected by the V/III ratio in the gas phase. The incorporation efficiency of indium was observed to increase with higher growth rates and decreasing temperature, but was independent of the V/III ratio in the investigated parameter range. In_0.16Ga_0.84N single quantum wells showed intense quantum well related luminescence at room temperature, with a full width at half maximum of 7.9 nm at a thickness of 50 Å. Single quantum wells embedded in InGaN of graded composition showed superior properties compared to quantum wells with In_0.04Ga_0.94N barriers of constant composition.     

Control of the morphology of InGaN/GaN quantum wells grown by metalorganic chemical vapor deposition

Various techniques for morphological evolution of InGaN/GaN multiple quantum well (MQW) structures grown by metalorganic chemical vapor deposition have been evaluated. Atomic force microscopy, photoluminescence (PL) and X-ray diffraction measurements have been used for characterization. It is shown that inclusions, that are generated into the V-defects in the InGaN quantum wells (QW), can be removed by introducing a small amount of hydrogen during the growth of GaN barriers. This hydrogen treatment results in partial loss of indium from the QWs, but smooth surface morphology of the MQW structure and improved optical quality of InGaN wells are obtained. The density of the V-defects could be reduced by reducing the dislocation density of the underlying GaN buffer.     

Influence of AlGaN/GaN/InGaN superlattice on the characteristics of LEDs grown by metalorganic chemical vapor deposition

This study examined the influence of strain-compensated triple AlGaN/GaN/InGaN superlattice structures (SLs) in n-GaN on the structural, electrical and optical characteristics of LEDs by analyzing the etch pits density (EPD), stress measurement, high-resolution X-ray diffraction (HRXRD), sheet resistance, photoluminescence (PL) and light–current–voltage (L–I–V). EPD, stress measurement and HRXRD studies showed that the insertion of AlGaN/GaN/InGaN SLs during the growth of n-GaN effectively distributed and compensated for the strong compressive stress, and decreased the dislocation density in n-GaN. The operating voltage at 20 mA for the LEDs grown with SLs decreased to 3.18 V from 3.4 V for the LEDs grown without SLs. In addition, a decrease in the spectral blue shift compared to the LEDs grown without SLs was observed in the LEDs grown with the SLs.     

Impact of the gas flow ratio on the physical properties of GaN grown by vertical flow metalorganic chemical vapour deposition

We studied the effect of gas flow ratio of the H₂ carrier gas to the NH₃ precursor on the physical and crystal properties of GaN. GaN was grown by vertical reactor metalorganic chemical vapour deposition (MOCVD) on a low-temperature-deposited GaN buffer layer. A (0 0 0 1) sapphire substrate was used. The impact of the gas flow ratio as it was varied from 0.25 to 1 was investigated and discussed. With increase in flow ratio, the concentrations of magnesium and carbon impurities in GaN increased. The flow ratio of 0.5 is the optimum value to minimise the background electron concentration and to maintain crystal quality. The decrease in the background electron concentration is due to the compensation mechanism of acceptor-like magnesium and carbon impurities.     

Photo-assisted growth of ZnTe by metalorganic chemical vapour deposition

The metalorganic chemical vapour deposition (MOCVD) photo-assisted growth of ZnTe using a xenon lamp has been performed at atmospheric pressure under hydrogen as a carrier gas. Epitaxial growth was achieved on (100) GaAs, (100) GaSb and (100) ZnTe substrates with diethylzinc (DEZn) and diethyltellurium (DETe) as precursors. We have studied the growth rate as a function of the growth temperature, the partial pressure of precursors, the inlet partial pressure ratio R = VI/II, the light intensity and the energy of the irradiating photons. A growth rate enhancement has been observed for illuminated layers grown on GaAs and ZnTe substrates in comparison with those grown without illumination. We have not observed any measurable enhancement for layers grown onto (100) GaSb. The growth rate as a function of the light intensity increases for intensities higher than 20 mW / cm² and saturates for P > 120 mW / cm². We relate the growth rate enhancement to irradiating photons with an energy higher than the band gap of ZnTe at the growth temperature.     

Correlations between photoluminescence and Hall mobility in GaN/sapphire grown by metalorganic chemical vapor deposition

We have investigated photoluminescence (PL) and electron Hall mobility for unintentionally doped GaN epitaxial layers grown by low-pressure metalorganic chemical vapor deposition on c-plane Al₂O₃ substrates. Four GaN films having identical dislocation density but remarkably different electron Hall mobility were exploited. At low temperature (12 K), a PL line associated with a bound exciton was observed and strong correlations were found between the Hall mobility and the PL intensity of the exciton transition. That is, relative PL intensity of the bound exciton to a donor-bound exciton monotonously increased with decreasing the electron mobility of the GaN films. This correlation was interpreted in terms of electrical compensation. Efforts to find the chemical origin of the PL line led to the conclusion that the BE line originated neither from threading dislocations nor from extrinsic point defects. Intrinsic acceptors such as Ga vacancy and GaN anti-site were suspected as plausible origin.     

Fabrication of a GaN lateral polarity junction by metalorganic chemical vapor deposition

A fabrication process for growth of GaN lateral polarity junctions consisting of Ga-polar and N-polar domains grown simultaneously side-by-side on c-plane sapphire was developed using the polarity control scheme. An ammonia-annealing step following deposition and patterning of a thin low-temperature AlN nucleation layer played a crucial role in avoiding mixed-polarity growth of the remaining AlN nucleation layer, as well as in nitriding the bare sapphire surface to facilitate growth of N-polar GaN. The achievement of both polar domains, free from inversion domains within a contiguous domain, led to Ga-polar domain exhibiting featureless morphology with highly resistive characteristics, while N-polar domains exhibited hexagonally faceted morphology and were highly conductive.     

Zn-doped AlInAs grown at high temperature by metalorganic chemical vapor deposition

Zn-doped AlInAs growth at high temperature, mainly at 750°C, by metalorganic chemical vapor deposition is investigated. When introducing DEZn during AlInAs growth, it is necessary to increase the TMAl flow rate in order to make the layer lattice-matched to InP. This is due to the enhanced In incorporation rather than the large covalent radius of Zn. To clarify the electrical characteristics, the dependence of the DEZn flow rate, the V/III ratio, and the growth temperature are investigated using the van der Pauw Hall method. In our growth system, a GaInAs intermediate layer is effective in preventing n-type inversion in Zn-doped AlInAs, which occurs when it is grown directly on an InP buffer layer. In addition, a large DEZn flow rate is effective for reducing carrier compensation in Zn-doped AlInAs layers grown at 750°C. Si impurities are apparently the cause of the type-inversion and compensation in Zn-doped AlInAs.     

N-face GaN growth on c-plane sapphire by metalorganic chemical vapor deposition

In this work, we report the growth of smooth, high-quality N-face GaN on c-plane sapphire by metalorganic chemical vapor deposition. It is found that the nitridation temperature of sapphire has a critical effect on the surface morphology of N-face GaN. Sapphire after a severe nitridation gives rise to a high density of hexagonal hillocks during N-face GaN growth. Smooth N-face GaN has been grown on appropriately nitridized sapphire. The N-polarity of the GaN film has been confirmed with no inversion domain by convergent beam electron diffraction. Controlled growth interruption is carried out to study the nucleation evolution during N-face GaN growth, which is found distinctly different from the two-step growth of Ga-face GaN. Atomically smooth N-face GaN has been achieved with comparable structural quality to Ga-face GaN.     

Polar dependence of impurity incorporation and yellow luminescence in GaN films grown by metal-organic chemical vapor deposition

We have investigated the unintentional impurities, oxygen and carbon, in GaN films grown on c-plane, r-plane as well as m-plane sapphire by metal-organic chemical vapor deposition. The GaN layer was analyzed by secondary ion mass spectroscopy. The different trend of the incorporation of oxygen and carbon has been explained in the polar (0 0 0 1), nonpolar (1 1 2¯ 0) and semipolar (1 1 2¯ 2) GaN by a combination of the atom bonding structure and the origin direction of the impurities. Furthermore, it has been found that there is a stronger yellow luminescence (YL) in GaN with higher concentration of carbon, suggesting that C-involved defects are originally responsible for the YL.     

Hydrogen removal by annealing from C-doped InGaAs grown on InP by metalorganic chemical vapor deposition

Hydrogen removal from C-doped InGaAs grown on InP substrate by metalorganic chemical vapor deposition is discussed based on the dependence of hole concentration on various annealing conditions. It is revealed that the hydrogen removal rate becomes higher as the annealing temperature is higher and the activation energy of hydrogen removal is about 1.9 eV regardless of C-doped layer thickness. The hydrogen removal rate is also found to be inversely proportional to C-doped layer thickness, suggesting that the hydrogen removal reaction is mainly governed by hydrogen diffusion.     

Growth and process modeling studies of nickel-catalyzed metalorganic chemical vapor deposition of GaN nanowires

A combination of experimental and computational fluid dynamics-based reactor modeling studies were utilized to study the effects of process conditions on GaN nanowire growth by metalorganic chemical vapor deposition (MOCVD) in an isothermal tube reactor. The GaN nanowires were synthesized on (0 0 0 1) sapphire substrates using nickel thin films as a catalyst. GaN nanowire growth was observed over a furnace temperature range of 800–900 °C at V/III ratios ranging from 33 to 67 and was found to be strongly dependent on the position of the substrate relative to the group III inlet tube. The modeling studies revealed that nanowire growth consistently occurred in a region in the reactor where the GaN thin-film deposition rate was reduced and the gas phase consisted primarily of intermediate species produced by the reaction and decomposition of trimethylgallium–ammonia adduct compounds. The GaN nanowires exhibited a predominant [1 1 2¯ 0] growth direction. Photoluminescence measurements revealed an increase in the GaN near-band edge emission intensity and a reduction in the deep-level yellow luminescence with increasing growth temperature and V/III ratio.     

Optical and structural properties of epitaxial GaN films grown by pulsed laser deposition

Epitaxial GaN films have been grown on c-cut sapphire substrates by pulsed laser deposition (PLD) using a KrF laser. The properties of GaN films were improved by increasing the growth temperature to 800°C and the nitrogen pressure during growth to 10 mTorr. Room-temperature photoluminescence exhibits a strong band-edge emission at 3.4 eV. From transmission electron microscopy (TEM), the predominant defects in PLD-GaN observed are stacking faults parallel to the interface and screw dislocations along c-axis, the latter differing from the previously published results where most of the threading dislocation in GaN grown by other techniques are of edge type with Burgers vector of .     

Compensation effect of Mg-doped a- and c-plane GaN films grown by metalorganic vapor phase epitaxy

The electrical and optical properties of Mg-doped a- and c-plane GaN films grown by metalorganic vapor phase epitaxy were systematically investigated. The photoluminescence spectra of Mg-doped a- and c-plane GaN films exhibit strong emissions related to deep donors when Mg doping concentrations are above 1×10²⁰ cm⁻³ and 5×10¹⁹ cm⁻³, respectively. The electrical properties also indicate the existence of compensating donors because the hole concentration decreases at such high Mg doping concentrations. In addition, we estimated the N_D/N_A compensation ratio of a- and c-plane GaN by variable-temperature Hall effect measurement. The obtained results indicate that the compensation effect of the Mg-doped a-plane GaN films is lower than that of the Mg-doped c-plane GaN films.     

Microstructure of hydrogenated silicon carbide thin films prepared by chemical vapour deposition techniques

We present the results of investigations on a variety of stoichiometric μc-SiC:H films deposited by Hot-Wire- and Plasma-Enhanced Chemical Vapour Deposition using monomethylsilane diluted in hydrogen as precursor gas. Infrared spectroscopy, grazing incidence X-ray diffraction, and Transmission Electron Microscopy were applied and compared to separate the contributions from the different structure phases of the material. It is shown that an evaluation of the crystalline volume fraction from the infrared absorption lineshape of the Si–C stretching mode is not possible, although stated in the literature. A correlation of this lineshape with the material strain is proposed. Moreover, a variation in strain, grain size, and structural defects is found depending on the deposition conditions, but a mixture of an amorphous and a crystalline phase could not unambiguously be identified.     

Paramagnetic defects in diamond films synthesized by the hot filament chemical vapour deposition

Defects in nitrogen‐doped diamond films, produced by hot filament chemical vapour deposition have been studied by Electron Spin Resonance (ESR), Raman spectroscopy and Scanning Electron Microscopy (SEM). The peak‐to‐peak ESR line width (ΔH _pp) varies in the range 0.36‐0.52 mT and depends on the nitrogen concentration in the process gas. In the case of nitrogen‐doped diamond films ESR spectrum shows a hyperfine structure typical of N_S⁰ paramagnetic centre. The shape of the central ESR line shows that it is a superposition of two components: a narrower Lorentzian and a broader Gaussian one, characterized by different saturation behaviour. With increasing nitrogen concentration in process gas the ratio of integral intensities A _G/A _L (Gausian to Lorentzian) of ESR spectrum also increases. The Raman spectra show that with increasing doping level the diamond Raman line at 1332.5 cm^‐1 broadens, the broad band at about 1530 cm^‐1 becomes more pronounced what indicate on degradation of diamond crystallinity and it is in agreement with SEM observation. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of thick,continuous GaN layers on 4-in. Si substrates by metalorganic chemical vapor deposition

We report on the growth of thick GaN epilayers on 4-in. Si(1 1 1) substrates by metalorganic chemical vapor deposition. Using intercalated AlN layers that contribute to counterbalance the tensile strain induced by the thermal mismatch between gallium nitride and the silicon substrate, up to 6.7 μm thick crack-free group III-nitride layers have been grown. Root mean-squares surface roughness of 0.5 nm, threading dislocation densities of 1.1×10⁹ cm^?2, as well as X-ray diffraction (XRD) full widths at half-maximum (FWHM) of 406 arcsec for the GaN(0 0 2) and of 1148 arcsec for the GaN(3 0 2) reflection have been measured. The donor bound exciton has a low-temperature photoluminescence line width of 12 meV. The correlation between the threading dislocation density and XRD FWHM, as well as the correlation between the wafer curvature and the GaN in-plane stress is discussed. An increase of the tensile stress is observed upon n-type doping of GaN by silicon.     

Photoluminescence of InGaN/GaN multiple quantum wells grown by mass transport

We report on studies of an In_0.12Ga_0.88N/GaN structure with three 35 Å thick quantum wells (QWs) grown by metalorganic vapor phase epitaxy with employment of mass transport. The mass-transport regions demonstrate a threading dislocation density less than 10⁷ cm⁻². The photoluminescence (PL) spectrum is dominated by a 40 meV—narrow line centered at 2.97 eV at 2 K. This emission has a typical PL decay time of about 5 ns at 2 K within the PL contour. An additional line with longer decay time (about 200 ns) is observed at an energy about 2.85 eV. The position of this line shifts towards higher energies with increasing excitation power. The data are consistent with a model, where the PL originates from at least two nonequivalent QWs, which could be realized due to a potential gradient across the layers.     

Radical-assisted metalorganic chemical vapor deposition of ZnSe

Radical-assisted metalorganic chemical vapor deposition (MOCVD) of ZnSe has been performed by using diethylzinc (DEZn) and diethylselenide (DESe) as a source and azo-t-butane ((t-C₄H₉)₂N₂)and nitrogen trifluoride (NF₃) as co-reactants. The growth rate was significantly increased in the measured temperature range of 623 to 723 K.