The incorporation behavior of arsenic and antimony in GaAsSb/GaAs grown by solid source molecular beam epitaxy

GaAsSb ternary epitaxial layers were grown on GaAs (0 0 1) substrate in various Sb₄/As₂ flux ratios by solid source molecular beam epitaxy. The alloy compositions of GaAs_1−ySb_y were inferred using high-resolution X-ray symmetric (0 0 4) and asymmetric (2 2 4) glance exit diffraction. The non-equilibrium thermodynamic model is used to explain the different incorporation behavior between the Sb₄ and As₂ under the assumption that one incident Sb₄ molecule produces one active Sb₂ molecule. It is inferred that the activation energy of Sb₄ dissociation is about 0.46 eV. The calculated results for the incorporation efficiency of group V are in good agreement with the experimental data.     

Coexistence properties of phase separation and CuPt-ordering in InGaAsP grown on GaAs substrates by organometallic vapor phase epitaxy

CuPt-ordering and phase separation were directly investigated in In_1-xGa_xAs_yP_1-y with a low arsenic content grown by organometallic vapor phase epitaxy on GaAs substrates. CuPt-ordering and phase separation in samples grown at the substrate temperatures of 630 and 690 °C were characterized by transmission electron diffraction and transmission electron microscopy. Although the immiscibility of InGaAsP was enhanced at the lower substrate temperature, the sample grown at 630 °C showed less phase separation than the 690 °C-grown sample. The degree of CuPt-ordering was significantly enhanced in the sample grown at 630 °C. The results demonstrated that the CuPt-ordering originating from surface reconstruction of P(2×4) suppressed the phase separation even in the miscibility gap. The detailed characterization of the phase separation clearly revealed a vertical composition modulation (VCM) in InGaAsP for the first time. The mechanism of the VCM formation is discussed based on the modulated-strain field on the surface.     

Metalorganic vapor-phase epitaxy of III/V phosphides with tertiarybutylphosphine and tertiarybutylarsine

Indium phosphide, gallium arsenide phosphide, and aluminum indium phosphide have been deposited by metalorganic vapor-phase epitaxy using tertiarybutylphosphine and tertiarybutylarsine. The effects of growth temperature and V/III ratio on the amount of silicon, sulfur, carbon, and oxygen in InP have been determined. Minimum incorporation was observed at 565 °C and a V/III ratio of 32. In this case, the material contained a background carrier concentration of 2.7×10¹⁴ cm⁻³, and the Hall mobilities were 4970 and 135,000 cm²/V s at 300 and 77 K. The oxygen contamination in AlInP was found to be only 9.0×10¹⁵ cm⁻³ for deposition at 650 °C and a V/III ratio of 35. The relative distribution of arsenic to phosphorus in GaAs_yP_1−y was determined at temperatures between 525 and 575 °C. The distribution coefficient [(N_As/N_P)_film/(P_TBAs/P_TBP)_gas] ranged from 25.4 to 8.4, and exhibited an Arrhenius relationship with an apparent activation energy of 1.2 eV.     

Atomic ordering in GaAsSb (0 0 1) grown by metalorganic vapor phase epitaxy

Epitaxial GaAsSb (0 0 1) semiconductor alloys grown by metalorganic vapor phase epitaxy exhibit several spontaneously ordered structures. A superlattice structure with three-fold ordering in the [1 1 0] direction has been previously observed by different groups. CuAu structures with (1 0 0) and (0 1 0) ordering planes have also been reported. The physical origin of CuAu ordering in III–V semiconductors has not yet been explained. In this work we report the effect of growth conditions on CuAu ordering in GaAsSb, including miscut from (0 0 1), growth rate, bismuth surfactant concentration, and growth temperature. These data point to a surface kinetic mechanism not based on dimer strain, but possibly due to one-dimensional ordering at step edges.     

Predicted nitrogen doping concentrations in silicon carbide epitaxial layers grown by hot-wall chemical vapor deposition

A simple quantitative model for the surface adsorption of nitrogen has been developed to simulate the doping incorporation in intentionally doped 4H–SiC samples during epitaxial growth. Different reaction schemes are necessary for the two faces of SiC. The differences are discussed, and implications to the necessary model adjustments are stressed. The simulations are validated by experimental values for a large number of different process parameters with good agreement.     

Kinetics of residual doping in 4H-SiC epitaxial layers grown in vacuum

Investigation on residual Al, B, and N co-doping of 4H-SiC epitaxial layers is reported. The layers were produced by sublimation epitaxy in Ta growth cell environment at different growth temperatures and characterized by secondary ion mass spectrometry. The vapor interaction with Ta was considered through calculations of cohesive energies of several Si-, Al-, B-, and N-containing vapor molecules and also of diatomic Ta–X molecules. An analysis of kinetic mechanisms responsible for impurity incorporation is performed. Among residuals, B exhibits a stronger incorporation dependence on temperature and growth at lower temperatures can favor B decrease in the layers. Under the growth conditions in this study (Ta environment and presence of attendant Al and N), B incorporation is assisted by Si₂C vapor molecule. Boron tends to occupy carbon sites at higher temperatures, i.e. higher growth rates.     

Influence of Be on N composition in Be-doped InGaAsN grown by RF plasma-assisted molecular beam epitaxy

Undoped and Be-doped InGaAsN layers were grown on GaAs substrates under the same growth conditions by radio frequency plasma-assisted molecular beam epitaxy. Increased tensile strain (Δa/a=3×10⁻³) was observed for Be-doped InGaAsN layers, compared to undoped InGaAsN layers. The strain is shown to originate from the increase in N composition related to Be incorporation, rather than solely from Be atoms substituting Ga atom sites (Be_Ga). A possible reason is the high Be–N bond strength, which inhibits the loss of N from the growth surface during epitaxial growth, thereby increasing the N composition in the Be-doped InGaAsN layer.     

Characterization of heterointerfaces in GaAs/MnAs/MnZn-ferrite structures

We have grown GaAs epitaxial films on MnZn-ferrite substrates using MnAs buffer layers and investigated their heterointerfaces with glazing incidence-angle X-ray reflectivity and X-ray photoelectron spectroscopy. It has been found that the heterointerfaces for this structure are quite abrupt and the roughness at the GaAs/MnAs and MnAs/MnZn-ferrite interfaces are 1.1 and 0.2 nm, respectively. We also found that the diffusion of atoms through the GaAs/MnAs interface into the GaAs film is negligible. These results indicate that the MnAs buffer layer for the GaAs/ferrite structure is chemically stable and promising for the application to the future magnetic electronics.     

Influence of semi-insulating InP substrates on InAlAs epilayers grown by molecular beam epitaxy

Tensile-strained InAlAs layers have been grown by solid-source molecular beam epitaxy on as-grown Fe-doped semi-insulating (SI) InP substrates and undoped SI InP substrates obtained by annealing undoped conductive InP wafers (wafer-annealed InP). The effect of the two substrates on InAlAs epilayers and InAlAs/InP type II heterostructures has been studied by using a variety of characterization techniques. Our calculation data proved that the out-diffusion of Fe atoms in InP substrate may not take place due to their low diffusion coefficient. Double-crystal X-ray diffraction measurements show that the lattice mismatch between the InAlAs layers and the two substrates is different, which is originated from their different Fe concentrations. Furthermore, photoluminescence results indicate that the type II heterostructure grown on the wafer-annealed InP substrate exhibits better optical and interface properties than that grown on the as-grown Fe-doped substrate. We have also given a physically coherent explanation on the basis of these investigations.     

Growth of embedded ErAs nanorods on (4 1 1)A and (4 1 1)B GaAs by molecular beam epitaxy

The low solubility of Er in GaAs results in the formation of ErAs nanostructures when GaAs is grown with 5–6 at% Er/Ga ratio by molecular beam epitaxy on GaAs surfaces. For growth on the (4 1 1)A GaAs surface, cross-sectional scanning transmission electron microscopy images show the presence of ErAs nanorods embedded in a GaAs matrix extending along the [2 1 1] direction with a spacing of roughly 7 nm and a diameter of roughly 2 nm. Growth on the GaAs (4 1 1)B surface resulted in only nanoparticle formation. Variation of the polarized optical absorption with in-plane polarization angle is consistent with coupling to surface plasmon resonances of the semimetallic nanostructures.     

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.     

Enhanced growth rates and reduced parasitic deposition by the substitution of Cl2 for HCl in GaN HVPE

The main limitation in the application of hydride vapor phase epitaxy for the large scale production of thick free-standing GaN substrates is the so-called parasitic deposition, which limits the growth time and wafer thickness by blocking the gallium precursor inlet. By utilizing Cl₂ instead of the usual HCl gas for the production of the gallium chlorine precursor, we found a rapid increase in growth rate from ∼80 to ∼400 μm/h for an equally large flow of 25 sccm. This allowed us to grow, without any additional optimization, 1.2 mm thick high quality GaN wafers, which spontaneously lifted off from their 0.3° mis-oriented GaN on sapphire HCl-based HVPE templates. These layers exhibited clear transparencies, indicating a high purity, dislocation densities in the order of 10⁶ cm⁻², and narrow rocking curve XRD FWHMs of 54 and 166 arcsec in for the 0002 and 101−5 directions, respectively.     

Ga assisted oxide desorption on GaAs(0 0 1) studied by scanning tunnelling microscopy

Native oxide removal on GaAs wafers under conventional thermal desorption causes severe surface degradation. Recently a new method of Ga assisted oxide removal has reported improved initial surface conditions. A precise dosing of Ga is required to optimise the oxide removal, however the effects of alternate temperatures on the desorption process effects the reaction kinetics. By using selected bias imaging, scanning tunnelling microscopy (STM) can be used to probe the underlying bulk whilst the native oxide is still present. Hence the effects of oxide removal on the surface can be identified during the native oxide desorption. By comparing Ga assisted oxide removal on both vicinal and off cut samples, the Ga adatom kinetics are shown to underpin the oxide removal process and a sample temperature in excess of 500 °C is necessary to optimise the procedure.     

Incorporation behaviors of group V elements in GaAsSbN grown by gas-source molecular-beam epitaxy

We report the incorporation behaviors of As, Sb, and N atoms in GaAsSbN grown by gas-source molecular-beam epitaxy. We found that N atom is more reactive and competitive than Sb atom at the growth temperature ranging from 420 to 450 °C. The increment in Sb beam flux hardly changes the N composition. However, the increment in N flux retards the incorporation of Sb. In addition, the increment in As₂ flux makes the Sb and N compositions decrease at the same rate. Based on these results, we have successfully grown GaAsSbN epilayers lattice-matched to GaAs substrates. The energy gap at room temperature is as low as 0.803 eV. Negative deviation from Vegard's law in lattice constant is observed in these layers.     

GaN/GaAs(1 0 0) superlattices grown by metalorganic vapor phase epitaxy using dimethylhydrazine precursor

Superlattices of cubic gallium nitride (GaN) and gallium arsenide (GaAs) were grown on GaAs(1 0 0) substrates using metalorganic vapor phase epitaxy (MOVPE) with dimethylhydrazine (DMHy) as nitrogen source. Structures grown at low temperatures with varying layer thicknesses were characterized using high resolution X-ray diffraction and atomic force microscopy. Several growth modes of GaAs on GaN were observed: step-edge, layer-by-layer 2D, and 3D island growth. A two-temperature growth process was found to yield good crystal quality and atomically flat surfaces. The results suggest that MOVPE-grown thin GaN layers may be applicable to novel GaAs heterostructure devices.     

Fluid-dynamics during vapor epitaxy and modeling

Epitaxial deposition of thin or thick solid films is one of the most important growth processes in opto- and micro-electronic device production. The performance of growth apparatuses depend strongly on the physical and chemical aspects involved in the deposition process, such as the fluid dynamic features and the deposition chemistry. These phenomena can be well described through a macroscale modeling approach based on fundamental conservation equations. These models can be successfully adopted to optimize existing processes and to design new reactors where the “flat area” matching industrial needs is always increasing in time. Here, a macroscale model for deposition reactors has been derived highlighting the hypotheses necessary to fit the general conservation equations for these systems. Moreover, attention has been placed on the estimation of the necessary physical and chemical parameters. Macroscale aspects have been addressed with particular emphasis on the role of fluid flow within the reactor to reveal desired or undesired flow paths and their effect on process performance parameters. In particular, horizontal, vertical and barrel reactor types have been examined.     

Reduction of threading dislocations in migration enhanced epitaxy grown GaN with N-polarity by use of AlN multiple interlayer

High quality GaN layer was obtained by insertion of high temperature grown AlN multiple intermediate layers with migration enhanced epitaxy method by the RF-plasma assisted molecular beam epitaxy on (0 0 01) sapphire substrates. The propagating behaviors of dislocations were studied, using a transmission electron microscope. The results show that the edge dislocations were filtered at the AlN/GaN interfaces. The bending propagation of threading dislocations in GaN above AlN interlayers was confirmed. Thereby, further reduction of dislocations was achieved. Dislocation density being reduced, the drastic increase of electron mobility to 668 cm²/V s was obtained at the carrier density of 9.5×10¹⁶ cm⁻³ in Si doped GaN layer.