FWHM Of X-ray Rocking Curve Research Articles

Growth of beta barium borate (β-BaB 2O 4) thin films on alpha barium borate (α-BaB 2O 4) substrates

Crystalline β-BBO thin films have been successfully prepared on (0 0 1)-oriented Sr 2+-doped α-BBO substrates using liquid phase epitaxy and pulsed laser deposition techniques. The films were characterized by X-ray diffraction and X-ray rocking curve (XRC). The present results manifest that the β-BBO thin films grown on Sr 2+-doped α-BBO substrates have larger degree of orientation f-value and smaller XRC FWHM than the ones grown on other reported substrates. Compared with other substrates, α-BBO has the same UV cutoff and the similar structure to β-BBO. These results reveal that α-BBO single crystal may be a promising substrate proper to the growth of β-BBO films.

Structural and optical characterization of epitaxial layers of CdTe/PbTe grown on BaF 2 (111) substrates

CdTe and CdTe/PbTe layers were grown on BaF2 (111) substrates by molecular beam epitaxy technique employing PbTe, CdTe, and Te2 effusion cells. The layers are monocrystalline with (111) crystal orientation and exhibit x-ray rocking curve FWHM parameter of 100-300 arcsec for PbTe and CdTe. The well defined streaky RHEED diffraction pattern was observed during the process of growth of both layers indicating a two-dimensional mode of growth. For the optical characterization of CdTe layers, the photoluminescence spectra were studied at T = 4.2 K in 750–870 nm (1.40–1.65 eV) spectral range using pulsed excitation at 2.35 eV by Nd:YAG laser. In CdTe/BaF2 layers, the dominant photoluminescence peak is observed at 785 nm and corresponds to the radiative recombination of excitons bound to neutral acceptors. In CdTe/PbTe/BaF2 heterostructures with thick PbTe buffer, no photoluminescence is observed in the spectral range studied. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Growth and characterization of GaN films on Si(111) substrate using high-temperature AlN buffer layer

Hexagonal GaN films exceeding 1 μm have been prepared on Si(111) substrates using high-temperature AlN buffer layers, and no cracks were observed. The FWHM of X-ray rocking curve for GaN (0002) was 560 arcsec. Strong band-edge photoluminescence (PL) was present in PL spectra. Micro-Raman spectra using shifts of E 2 phonon showed that GaN films were in compressive stress, which agreed with the characterization result of X-ray lattice parameters method.

Effect of Strain Gradation on Luminescence and Electronic Properties of Pulsed Laser Deposited Zinc Oxide Thin Films

ZnO thin films were grown by ablation of a ZnO ceramic target using pulsed excimer laser (KrF) under 1 mTorr oxygen partial pressure over (0001) α -Al2O3 substrates held at 750_∘C. Highly c-axis oriented (0002) ZnO films with visible range optical transparency over 80% were obtained. Inhomogeneous distribution of strain in the film growth direction was studied by line shape analysis of X-ray diffraction and broad luminescence features centered on near band edge transition at 3.3 eV. Strain in the film adversely affects optical gain and excitonic threshold of UV emission. Post-growth oxygen annealing of films at 850°C for 1 h reduces strain and associated defects at ZnO film interface with (0001) Al2O3 substrate. FWHM of X-ray rocking curves show corresponding lowering from 12.5 arc min to 9.0 arc min signifying improved ZnO crystal quality. ω -rocking curves show line features with two superimposed peaks belonging to interfacial layer and bulk ZnO film. Graded strain in ZnO film is related to differently oriented interfacial layer formed at inception stage of film growth. Decrease in conductivity of annealed ZnO films show that O2-vacancies are primary defects. Formation of strain free (0002) oriented optical quality ZnO films based on combined process of growth in low O2 pressure and post growth anneal at high O2 pressure is proposed for UV-optoelectronic applications.

Properties of RF magnetron sputtered zinc oxide thin films

ZnO thin films were deposited on silicon substrate by RF magnetron sputtering using metallic zinc target. A systematic study has been made of the influence of oxygen concentration and the RF power on the films structural properties. They exhibited a c-axis orientation of below 0.32° FWHM of X-ray rocking curves, an extremely high resistivity of 10 12 Ω cm and an energy gap of 3.3 eV at room temperature. It was found that a RF power of 50 W, target to substrate distance 70 mm, very low gas pressures of 3.35×10 −3 Torr in argon and oxygen mixed gas atmosphere giving to ZnO thin films a good homogeneity and a high crystallinity.

Iodine vapor phase growth of GaN: dependence of epitaxial growth rate on process parameters

High quality GaN epitaxial films have been grown on sapphire using iodine vapor phase growth (IVPG). The growth mechanism has been investigated to determine the effect of pressure, flow rate, and V–III ratio on the crystalline quality of GaN epi-layers. A major distinction between this process and conventional hydride vapor phase epitaxy (HVPE) is the replacement of HCl gas by iodine as a reactant. Ammonia is the source of nitrogen, and forming gas or hydrogen is used as carrier gas. C-plane sapphire wafers with pre-deposited 1 μm MOCVD films were used as substrates. Growth conditions were investigated in the range of pressure between 1 and 0.1 atmosphere, while maintaining the same temperature gradient and mass flow rates for the reactant gases. Within these parameters, it was found that the fastest growth rate for GaN layers is obtained at vapor pressures close to equilibrium. The data indicates crystal quality is also optimized under these conditions. Crystal quality was determined from the FWHM of X-ray rocking curves and room temperature photoluminescence (PL). The crystal quality was found to improve under conditions where the ambient pressure and supersaturation approach equilibrium.

Growth and crystal properties of Tl-doped PbTe crystals grown by Bridgman method under Pb and Te vapor pressure

Growth of high-quality Tl-doped p-type PbTe single crystals by Bridgman method under controlled Te or Pb vapor pressure has been investigated. For high concentration of Tl in the melt (0.65 at%), the hole concentrations for crystals grown under applied Pb vapor pressures (1.5×10 19–2×10 19 cm −3) are higher than those for crystals grown under applied Te vapor pressures (5×10 18–8×10 18 cm −3). For low concentration of Tl (0.082 at%), the hole concentration is decreased with increasing Te vapor pressure. The PbTe crystals grown with high concentration of Tl under applied Pb vapor pressures show small FWHM of X-ray rocking curve ranging from 20 to 50 arcsec. Their etch pit densities are in the range of 8×10 4–6×10 5 cm −2, which are an order of magnitude lower than those of undoped PbTe crystals. These results indicate that highly Tl-doped (0.65 at%) PbTe crystals, in particular, those grown under applied Pb vapor pressure, have an excellent crystal quality.

ZnSe/ZnMgSSe structures on ZnSSe substrates

ZnS x Se 1− x ( x=0.08–0.12) substrates transparent for ZnSe QW emissions were used for the growth of ZnSe/ZnMgSSe structures. The FWHM of X-ray rocking curves of the substrates were 36–38 arcsec. Etching the substrate in diluted HCl to remove the oxide layer was performed as final treatment before the epitaxy. A variety of ZnSe/ZnMgSSe QW structures were grown by low-pressure MOVPE. All structures grown have strong ZnSe QW emissions in their PL spectra. For a MQW structure with intended well thicknesses of 4, 6 and 12 nm, well-resolved peaks of all QWs were observed.

ZnSe/ZnMgSSe QW structures grown by MOVPE on transparent ZnSSe substrates

ZnSSe substrates transparent for ZnSe QW emissions were used for the growth of ZnSe/ZnMgSSe structures. The FWHM of X-ray rocking curve of a substrate with a sulfur content of 8% was 38 arcsec. Effectively emitting ZnSe/ZnMgSSe QW structures of different specifications were grown by LP MOVPE. It was confirmed that etching the substrate surface in diluted HCl before growth improves the radiative properties of the grown structures due to a removal of oxide layers. For a QW structure with well thicknesses of 4 nm, 6 nm and 12 nm, well-resolved peaks of all QWs were observed in the low temperature PL spectra.

Characteristics of Fielo-GaN Grown by Hydride Vapor Phase Epitaxy

ABSTRACTThe crystal quality of facet-initiated epitaxial lateral overgrowth (FIELO) -GaN, in particular, that in the vicinity of the GaN surface, is reported. It is shown that the surface smoothness of FIELO-GaN enables us to use it as an “epi-ready” substrate. The crystallinity of FIELO-GaN is evaluated by x-ray rocking curve (XRC) measurements. We indicate that the FWHM of XRC should be reduced with the decrease of the dislocation density. We previously reported that the dislocation behavior of FIELO-GaN causes the tilting of the c-axis in the overgrown regions. By using scanning reflection electron microscopy (SREM), however, we show that the tilting on the surface of thick FIELO-GaN was negligibly small.

Effects of Susceptor Geometry on Gan Growth on Si(111) with a New MOCVD Reactor

High quality GaN films on AlN buffer layers were grown on Si(111) with a new, commercial, two-injector vertical rotating disk MOCVD reactor (CVD, Inc.). It was found that the geometry of the susceptor greatly affected the structural quality of the epilayers on Si. For the original susceptor geometry, though single crystal GaN films could be obtained, the films were dark gray in appearance with a rough morphology, and the best x-ray rocking curve FWHM was 2.33°. After modifying the susceptor geometry, transparent, mirror-like single crystal GaN films were obtained with the best x-ray rocking curve FWHM being 0.24°. Photoluminescence (PL) and infrared reflectance (IR) spectra of the grown films were compared. The film growth rate was found to increase with decrease of the growth pressure. A 2-D simulation of the flow, heat transfer, and chemical species transport in the reactor showed a more symmetric flow, larger velocity gradient, and lower upward velocity with the modified susceptor, which may be the main reason for the improvement of the structural quality of the films.

Epitaxial Growth of the GaN Film by Remote-Plasma Metalorganic Chemical Vapor Deposition

GaN films were successfully grown by the remote-plasma metalorganic chemical vapor deposition (RPMOCVD) system. The composition of the GaN films could be tuned from nitrogen-rich to stoichiometric growth by varying the mole flow rate of trimethylgallium (TMGa). A hypothesis concerning the collisions between excited nitrogen and TMGa was also brought up. The collision between excited nitrogen and TMGa influences the characteristics of surface morphology, composition, growth rate, and growth mechanism. The characteristics of the GaN film were optimized by changing the growth conditions. The narrowest FWHM of the double-crystal X-ray rocking curve is about 0.2°. Under optimized conditions, the composition of the GaN film is almost the same as that of the reference GaN film grown by MOCVD.

Atomically flat (0 0 1)GaAs surface prepared by two-step atomic-hydrogen treatment and its application to heteroepitaxy of GaN

Substrate surface treatment techniques and growth conditions are the key of growing high-quality cubic GaN (c-GaN) epitaxial layers on (001) GaAs substrates. An atomically flat (001) GaAs substrate surface can be obtained by a two-step atomic hydrogen (atomic-H) irradiation technique. The typical surface of the substrate treated by the atomic-H consists of narrow terraces of one monolayer step height with acute-angle polygonal structures. The X-ray rocking curve FWHM of GaN (002) grown on the atomic-H treated substrate is less than 90arcsec. It is shown that high-density monolayer steps and kinks at the surface terrace edge would be preferable for the uniform nucleation of the c-GaN buffer layer.

Effects of Susceptor Geometry on GaN Growth on SI(111) with a New Mocvd Reactor

AbstractHigh quality GaN films on AIN buffer layers were grown on Si(111) with a new, commercial, two-injector vertical rotating disk MOCVD reactor (CVD, Inc.). It was found that the geometry of the susceptor greatly affected the structural quality of the epilayers on Si. For the original susceptor geometry, though single crystal GaN films could be obtained, the films were dark gray in appearance with a rough morphology, and the best x-ray rocking curve FWHM was 2.33°. After modifying the susceptor geometry, transparent, mirror-like single crystal GaN films were obtained with the best x-ray rocking curve FWHM being 0.24°. Photoluminescence (PL) and infrared reflectance (IR) spectra of the grown films were compared. The film growth rate was found to increase with decrease of the growth pressure. A 2-D simulation of the flow, heat transfer, and chemical species transport in the reactor showed a more symmetric flow, larger velocity gradient, and lower upward velocity with the modified susceptor, which may be the main reason for the improvement of the structural quality of the films.

High Resistivity GaN Single Crystalline Substrates

High resistivity 104 -106 Ω cm (300 K) GaN single crystals were obtained by solution growth under high Ν2 pressure from melted Ga with 0.1-0.5at.% of Mg. Properties of these crystals are compared with properties of conductive crystals grown by a similar method from pure Ga melt. In • particular, it is shown that Mg-doped GaN crystals have better structural quality in terms of FWHM of X-ray rocking curve and low angle boundaries. Temperature dependence of electrical resistivity suggests hopping mechanism of conductivity. It is also shown that strain free GaN homoepitaxial layers can be grown on the Mg-doped GaN substrates. PACS numbers: 71.55.Eq, 72.80.Ey

Effect Of Atomic-Hydrogen Treatment Of (001) Gaas Substrate At “High Temperatures” On Rf Plasma-Assisted Molecular Beam Epitaxy Of Cubic Gan

AbstractsGrowth of high quality c-GaN on atomic-H treated (001) GaAs was examined by rf plasma-assisted MBE. First the initial growth stages (atomic-H treatment of GaAs, nitridation/deposition of a thin GaN buffer layer, the post deposition annealing of the buffer layer, and epitaxy of c-GaN) were studied by RHEED and AFM observations. It was found that atomically flat GaAs surface with one monolayer-height steps and ragged step edges could be obtained by the atomic-H treatment at high temperatures. It was found that the atomic-H treated GaAs surface was preferable to grow high quality c-GaN; the FWHM of the X-ray rocking curve for the (002) c-GaN was as small as 70 – 90 arcsec.

Investigation Of Nucleation And Initial Stage Of Gan Growth By Atomic Force Microscopy And X-Ray Diffraction

AbstractThe nucleation and initial stage of GaN growth on sapphire was investigated by atomic force microscopy, X-ray diffraction and photoluminescence. A 15 to 30 nm thick GaN buffer layer deposited at proper conditions was extremely smooth and nearly amorphous. Proper post deposition annealing resulted in the buffer crystallized. The buffer layer deposition temperature, thickness and annealing time and temperature must be coordinated. Low deposition temperature and/or insufficient annealing of the buffer results in a GaN wafer which has fine spiking surface morphology with an RMS of 3.4 nm for 1.4 μm wafer, strong yellow luminescence and wide xray rocking curve FWHM. High deposition temperature, longer crystallization time, and a low growth rate results in a wafer which exhibits strong band edge luminescence without noticeable yellow luminescence, and a narrow (002) diffraction rocking curve. However, the surface morphology exhibits well developed hexagonal feature with RMS roughness of 14.3 nm for a 570 nm thick layer. X-ray rocking curve analysis revealed buffer crystallization, domain coalescence and alignment process. The FWHM of the ω–scan of GaN (101) diffraction was 1700–2000 arc seconds for 200–1400 nm wafers which indicates that the twist of the domains is not changing much with the growth.

Heteroepitaxy of HgCdTe(112) infrared detector structures on Si(112) substrates by molecular-beam epitaxy

High-quality, single-crystal epitaxial films of CdTe(112)B and HgCdTe(112)B have been grown directly on Si(112) substrates without the need for GaAs interfacial layers. The CdTe and HgCdTe films have been characterized with optical microscopy, x-ray diffraction, wet chemical defect etching, and secondary ion mass spectrometry. HgCdTe/Si infrared detectors have also been fabricated and tested. The CdTe(112)B films are highly specular, twin-free, and have x-ray rocking curves as narrow as 72 arc-sec and near-surface etch pit density (EPD) of 2 × 106 cm−2 for 8 µm thick films. HgCdTe(112)B films deposited on Si substrates have x-ray rocking curve FWHM as low as 76 arc-sec and EPD of 3-22 × 106 cm−2. These MBE-grown epitaxial structures have been used to fabricate the first high-performance HgCdTe IR detectors grown directly on Si without use of an intermediate GaAs buffer layer. HgCdTe/Si infrared detectors have been fabricated with 40% quantum efficiency and R0A = 1.64 × 104 Ωm2 (0 FOV) for devices with 7.8 µm cutoff wavelength at 78Kto demonstrate the capability of MBE for growth of large-area HgCdTe arrays on Si.

Molecular beam epitaxial growth of [formula omitted] and [formula omitted] heteroepitaxial layers (thermodynamic analysis and characterization)

In this paper we present the detailed thermodynamic analysis and experimental study on the MBE growth process of heteroepitaxial InSb layers on strongly lattice-mismatched GaAs(100) and Si(100) substrates. A good qualitative agreement between theoretical and experimental results has been obtained. The influence of growth parameters ( T sub, Sb 4 In flow ratio) on the structural, electrical, and luminescence characteristics of the layers has been also investigated. The increase of T sub from 350 to 420°C together with the Sb 4 In flow ratio reduction result in a mirror-like surface morphology, decrease in X-ray rocking curve FWHM values and dislocation density down to 210 arcsec and 1 × 10 8 cm −2, respectively, and the disappearance of stacking faults. It also provides a lower unintentional doping level ( n ∼ 2.8 × 10 16 cm −3) in undoped layers and a higher electron mobility (51000 cm 2/V · s at 300 K and 36000 cm 2/V · s at 77 K). Using Be as a p-type dopant has been shown to enable to reach readily the Be doping level of InSb GaAs and InSb Si as high as 2 × 10 19 cm −3.

The growth and characterization of high quality UPt3 crystals

Single crystals of UPt3 have been prepared. The crystals are shown to have a superconducting transition temperature of 526±2 mK with a transition width of 12.6 ± 0.1 mK. The measured x-ray rocking curve FWHM of the (002) peak is 180 ± 5 arcseconds, compared to a theoretical minimum linewidth as predicted for a perfect UPt3 single crystal of 90 arcseconds. The x-ray characterization, susceptibility, residual resistivity ratio (RRR) and impurity concentration results are presented.