Double-crystal X-ray Diffraction Rocking Curves Research Articles

Influences of ultrathin amorphous buffer layers on GaAs/Si grown by metal–organic chemical vapor deposition

In this work, a technique for the growth of GaAs epilayers on Si, combining an ultrathin amorphous Si buffer layer and a three-step growth method, has been developed to achieve high crystalline quality for monolithic integration. The influences of the combined technique for the crystalline quality of GaAs on Si are researched in this article. The crystalline quality of GaAs epilayer on Si with the combined technique is investigated by scanning electron microscopy, double crystal X-ray diffraction (DCXRD), photoluminescence, and transmission electron microscopy measurements. By means of this technique, a 1.8-µm-thick high-quality GaAs/Si epilayer was grown by metal–organic chemical vapor deposition. The full-width at half-maximum of the DCXRD rocking curve in the (400) reflection obtained from the GaAs/Si epilayers is about 163 arcsec. Compared with only using three-step growth method, the current technique reduces etch pit density from 3 × 106 cm−2 to 1.5 × 105 cm−2. The results demonstrate that the combined technique is an effective approach for reducing dislocation density in GaAs epilayers on Si.

Growth and Characterization of High-Quality, Relaxed In y Ga1−y N Templates for Optoelectronic Applications

Thick, high-quality InGaN layers can be used as templates for quantum well strain reduction in light-emitting diodes and as optical absorption layers in solar cell structures. Current InGaN growth technology, however, is primarily limited by V-pit formation and non-uniform indium composition. We report the growth and characterization of thick, strain-relaxed In y Ga1− y N layers, with 0.08 ≤ y ≤ 0.11, by metal organic chemical vapor deposition using the semibulk approach, which consists in periodic insertion of 2-nm GaN interlayers into the bulk In y Ga1− y N structure; these are then spike-annealed at 1000°C. Photoluminescence, x-ray diffraction, and scanning electron and atomic force microscopy revealed that the semibulk In y Ga1− y N had optical and electrical properties superior to those of conventional bulk In y Ga1− y N grown at the same temperature. Homogeneous indium content and substantial reduction of V-pit density were observed for the semibulk In y Ga1− y N films, even when grown above the critical layer thickness. Double-crystal x-ray diffraction rocking curves also revealed a one order of magnitude reduction of screw dislocation density in the semibulk In y Ga1− y N film compared with the bulk In y Ga1− y N film.

New Method of Distinguishing X-Ray Diffraction Curves about Laser Structure

Come up with a new method of rocking curves analysis, its using the software of the double-crystal X-ray diffraction rocking curves analysis to simulate vertical cavity surface emitting laser structure. Simulate the X-ray diffraction rocking curve of each part of laser structure, and then compare with the diffraction rocking curve of the overall structure in order to acquire the adscription of each diffraction peak, the method can also be applied to other semiconductor lasers. Compared with conventional PDF card library about diffraction position of all material peaks, the method has the advantages of fast and accurately to distinguish, high efficiency. In the end, the X-ray diffraction rocking curves analysis method is applied to the MOCVD growth of GaAs based vertical cavity surface emitting laser, and quoting strain relaxation mechanisms for explaining the reasons for the partial peak drifting.

Growth of AlN bulk single crystals on 4H‐SiC substrates and analyses of their structural quality and growth mode evolution

AbstractAluminium nitride (AlN) bulk single crystals were grown on off‐oriented 4H‐SiC substrates by the sublimation method. High‐quality crystals with about 25 mm in diameter and up to 5 mm in thickness were obtained with an optimized growth process. The crystals show hexagonal symmetry with well developed {10$\overline {1} $1} side facets. Confocal‐Raman spectroscopy and double‐crystal X‐ray diffraction rocking curve (DCXRD‐RC) measurements confirm the high structural quality of the grown crystals. In Raman spectroscopy, the full‐width at half maximum (FWHM) of E2(high) phonon mode decreases from 40 cm−1 for thin layers (800 µm) to 22 cm−1 for a 5 mm thick crystal, showing the improvement in quality with thickness. The DCXRD rocking curve FWHM obtained for a 5 mm thick crystal is about 120 arcsec. A basal plane bending of 100 arcsec is observed by rocking curve measurements while scanning 17 mm of the sample's diameter. Two kinds of growth modes namely, step flow growth and spiral growth modes were observed under similar growth conditions. This may be attributed to a slight variation of super‐saturation in the gas phase. In both cases, a single active hexagonal growth centre is formed. As‐grown surfaces have been found to be always Al‐polar. Wet chemical etching revealed both, threading type and basal‐plane dislocations (BPD) on the surfaces of the samples with total etch pit densities (EPDs) in the range of 8 × 105–1 × 106 cm−2.

Variation of ion-irradiation induced strain as a function of ion fluence in Si

Strain in Si induced by ion irradiation at temperatures of 200–400°C has been measured at room temperature. Quantitative analysis of the strain distribution produced by 750-keV Si ion implantation in Si substrates was characterized by double-crystal X-ray diffraction (DCXRD). Strain in the Si surface layer was determined by modeling the DCXRD rocking curve using the program Rocking curve Analysis by Dynamic Simulation (RADS) where a generated strain profile is iteratively fitted to the measured rocking curve.The strain was tensile, resulting from a vacancy excess, and measured as a function of irradiation temperature and ion fluence. For a given temperature, strain increased as a function of ion fluence until a strain maximum was attained and then relaxed via dislocation formation. The maximum strain attainable decreased with an increase in irradiation temperature as consistent with thermally activated dislocation formation.

Crystallographic tilt in GaN layers grown by epitaxial lateral overgrowth

The crystallographic tilt in GaN layers grown by epitaxial lateral overgrowth (ELO) on sapphire (0001) substrates was investigated by using double crystal X-ray diffraction (DC-XRD). It was found that ELO GaN stripes bent towards the SiNx mask in the direction perpendicular to seeding lines. Each side of GaN (0002) peak in DC-XRD rocking curves was a broad peak related with the crystallographic tilt. This broad peak split into two peaks (denoted as A and B), and peak B disappeared gradually when the mask began to be removed by selective etching. Only narrow peak A remained when the SiNx mask was removed completely. A model based on these results has been developed to show that there are two factors responsible for the crystallographic tilt: One is the non-uniformity elastic deformation caused by the interphase force between the ELO GaN layer and the SiNx mask. The other is the plastic deformation, which is attributed to the change of the threading dislocations (TDs)-from vertical in the window regions to the lateral in the regions over the mask.

Characterization of strain relaxation in low-defect-density thin singleand step-graded germanium buffer layers by high-resolution two-dimensionalx-ray diffraction mapping

Double-crystal x-ray diffraction rocking curves and two-dimensionalreciprocal space mapping (2D-RSM) are utilized to characterize the degree ofstrain relaxation, lattice parameters and assessment of defect propagation intwo growth approaches to yield relaxed germanium buffer layers on siliconsubstrates. Two schemes are investigated: direct epitaxy of a single relaxedbuffer layer (SE-RBL) and step-graded multiple relaxed buffer layers(GM-RBLs). The characteristics of these two growth schemes offer prospects ofa much thinner grown layer compared with previously reported approaches.Two-dimensional reciprocal space mapping shows that an SE-RBL with a thicknessof less than 0.35 µm has a superior quality over the GM-RBLs. A highrelaxation factor (R = 0.986±0.002) is obtained from the asymmetric (113)2D-RSM of the SE-RBL with 100% Ge content. Further, the ratios of full widthat half maximum of the layer to substrate FWHM (L/S) of nearly unity forboth ω and ω/2θ scan directions imply a very high-qualitycrystalline relaxed buffer layer is realized. The 2D-RSM of the materialdeposited using the GM-RBL scheme, the first of its kind regarding the totalgrown thickness (approximately 6 µm), also show a mosaic final Gebuffer layer with an indication of reduction of dislocation density.

PROPERTIES OF ELECTRON CYCLOTRON RESONANCE PLASMAS AND THEIR INFLUENCE ON THE DEPOSITION OF GaN FILMS

Langmuir probes and Faraday cups have been used to characterize electron cyclotron resonance plasmas which have been used in the depositions of GaN films on the substrate of (0001)α-Al2O3.These plasmas were generated with microwave power(Pw) from 300W to 1100W at pressures(p) range from 0.8Pa to 0.05Pa using N2 as the plasma source.The relationship between the plasma parameter,such as ion density(Ni),electron temperature(Te),plasma potential(Vp) and ion current density(Ji),and system parameters,such as pW and p,is given.And the axial and radial distributions of Te,Ni,Vp and Ji are presented.The growth rate and the quality of the GaN film strongly depend on the growth condition.The higher the plasma density,the higher the N/Ga ratio of GaN film.When the microwave power was 850W and gas pressure was 0.22Pa,the plasma near the substrate was characterized by a Te near 1.4eV and plasma density near 2.0×1011 cm-3,and the growth rate of GaN was as high as 0.9μm/h.The full width at half maximum of double-crystal X-ray diffraction rocking curve is 16 arcmin.

X-ray diffraction from low temperature ion implanted silicon

Double-crystal X-ray diffraction rocking curves (RCs) have been measured at 77 K for silicon wafers implanted with 3 MeV Ni ions at 130 K. Rather symmetric broadening of RC of the sample implanted with 1 × 10 14 Ni 3+ /cm 2 was observed. It may be a kind of distortion scattering caused by vacancies, interstitials and their agglomerates. Modulated profile of the sample implanted with 4 × 10 14 Ni 3+ /cm 2 is a result of the nonuniform strain distribution. By further implantation, the modulating profile changes to a rather monotonous shape. It is considered to be a result of the strain fluctuation in an identical depth and the increasing of amorphous region reducing the coherency of X-rays. The annealing experiments were also carried out up to 1073 K. The change of RCs started even below room temperature and is rather continuous. It leads to the fact that the recovery of defects is rather continuous in temperatures. The recovery was completed at 1073 K. Numerical calculations for the depth profiles of the strain were carried out from the fitting of the simulated RCs to those observed.

High Quality ZnSe and Zn(Se,S) Produced by Low Temperature Physical Vapour Transport

High quality, large (25 mm in diameter) crystals of ZnSe and Zn(Se,S) were grown by low-temperature physical vapour transport method and characterized by various techniques, i.e. energy dispersive X-ray fluorescence spectrometry, double-crystal X-ray diffraction rocking curve FWHM, reflectivity measurements in the region of free exciton, electrical measurements and photoluminescence measurements for both low and high excitation densities. The measurement of the photoluminescence related to the neutral-donor-bound exciton revealed superlinear log(photoluminescence intensity) versus log(excitation intensity) dependence, which indicates stimulated emission phenomena.

Gas source molecular beam epitaxy of ZnSe and ZnSe:N

The use of gas source molecular beam epitaxy, using hydrogen selenide and elemental Zn as source materials, has resulted in the growth of high quality ZnSe on closely lattice-matched GaAs and (In,Ga)P. The undoped ZnSe epilayers are comparable in quality to material grown by molecular beam epitaxy, as indicated by narrow double-crystal x-ray diffraction rocking curves and intense photoluminescence dominated by a single donor-bound near-bandedge excitonic feature. Nitrogen species, derived from a radio frequency plasma source, are successfully used as acceptor impurities for ZnSe; photoluminescence spectra confirm the incorporation of nitrogen by the presence of the expected donor-to-acceptor pair recombination. Atomic concentrations of nitrogen as high as 5 x 1018 cm-3, are measured by secondary ion mass spectroscopy. Thus far, capacitance-voltage measurements indicate net acceptor concentrations (NA -ND) of approximately 1017 cm-3.

Growth of ( GaAs) 1− x( Si2) x metastable alloys using migration-enhanced epitaxy

( GaAs) 1* minus; x ( Si 2) x for 0< x<0.25 has been successfully grown on GaAs (100) substrates using migration-enhanced epitaxy. Structural and compositional analysis of the as-grown ( GaAs) 1− x ( Si 2) x layers indicated single phase epitaxial crystals with zincblende structure in the compositional range 0< x<0.25. The lattice constant a 0 of the alloys was found to decrease with increasing Si content from 0.56543 nm at x=0 to 0.5601 nm at x=0.25. Double-crystal X-ray diffraction rocking curve measurements and cross-sectional transmission electron microscopy studies carried out on a 10 period ( GaAs) 1− x ( Si 2) x / GaAs strained layer superlattice indicated sharp and abrupt interfaces of high crystalline quality.

High-quality ZnSe/GaAs superlattices: MEE growth, and structural and optical characterization

High-quality ZnSe/GaAs superlattices were grown by migration-enhanced epitaxy (MEE) and characterized using X-ray diffraction, electron microscopy and photoluminescence. The streaky reflection high-energy electron diffraction (RHEED) pattern and strong, persistent RHEED oscillations observed during the MEE growth of the superlattices indicate a smooth growing surface. The sharp satellite peaks observed clearly in the double-crystal X-ray diffraction rocking curve of a 21-period ZnSe/GaAs superlattice confirm the excellent crystalline and interfacial quality of the superlattice. Cross-section transmission electron microscopy (TEM) shows flat, abrupt heterointerfaces. Superlattice photoluminescence spectra show that both photo-excited electrons and holes are confined in GaAs wells; also seen are the sharp excitonic features from the coherently strained ZnSe cap and barrier layers of the superlattice.

Growth of (GaAs)1−x (Si2)x Metastable Alloys using Migration-Enhanced Epitaxy

ABSTRACTEpitaxial (GaAs)1−x (Si2)x metastable alloys have been grown on GaAs (100) substrates using Migration-Enhanced Epitaxy in the composition range of 0&lt;x&lt;0.25. The lattice constant a0 of the alloys was found to decrease with increasing Si content from 0.56543nm at x=0 to 0.5601nm at x=0.25. Double-crystal x-ray diffraction rocking curve measurements and cross-sectional transmission electron microscopy studies made on a 10 period (GaAs)1−x(Si2)x/GaAs strained layer superlattice indicated sharp and abrupt interfaces. High crystalline quality GaAs has been grown on Si substrates using (GaAs)0.80(Si2)0.20/GaAs strained layer superlattices as buffer layers.

Migration-enhanced epitaxy growth and characterization of high quality ZnSe/GaAs superlattices

We report the growth of high quality ZnSe/GaAs superlattices by migration-enhanced epitaxy (MEE) and their characterization using x-ray diffraction, electron microscopy, and photoluminescence. A streaky reflection high-energy electron diffraction (RHEED) pattern and strong, persistent RHEED oscillation during the MEE growth of the superlattices indicate a smooth growing surface. The sharp satellite peaks observed clearly in the double-crystal x-ray diffraction rocking curve of a 21-period ZnSe/GaAssuperlattice confirm the excellent crystalline and interfacial quality of the superlattice. Cross-section high-resolution electron microscopy indicates coherent lattice arrangement and abrupt interface at ZnSe-on-GaAs as well as GaAs-on-ZnSe heterointerfaces. Photoluminescence spectra from a superlattice with a periodicity of 40 nm show a strong peak at a wavelength of 829.5 nm with a linewidth of 6.3 meV at a temperature of 10 K; we believe this to be the first observation of photoluminescence from any multilayer structure involving GaAs-on-ZnSe growth.

THE GROWTH OF GaSb/AlSb/GaAs STRAINED LAYER HETEROSTRUCTURES BY MBE

By means of monitoring with the reflection high energy electron diffraction (RHEED) -and its intensity oscillations, the GaSb/AlSb/GaAs strained layer heterostructures have been suc-cessfully grown on semi-insulating (100) GaAs substrates by molecular beam epitaxy (MBE) The RHEED patterns show that the GaSb surface grown under Sb-stabilized condition has C (2×6) structure and the AlSb surface has (1×3) Sb structure. We observed and recorded the RHEED intensity oscillations during the growth of GaSb and AlSb. Using the information provided by the RHEED intensity oscillations, we successfully prepared a GaSb/AlSb super-lattice with 10 periods. The transmission electron micrograph shows the interfaces in the su-perlattice are sharp and planar. If the AlSb buffer layer is thick enough under a proper growth condition, a high-quality GaSb epitaxy will be grown on SI GaAs substrate. The full width at half maximun (FWHM) of the peak corresponding to the GaSb epilayer in double-crystal X-ray diffraction rocking curve is less than 300 seconds. Undoped GaSb is p-type with carrier concentration of 2.12×1016 cm-3 and mobility of 664cm2/V·s at room temperature.

Determination of epitaxic-layer composition and thickness by double-crystal X-ray diffraction

Double-crystal X-ray diffraction rocking curves can be used to evaluate composition and thickness of epitaxic layers. In order to assess the limits of this technique, the 004 rocking curves of molecular-beam epitaxy- (MBE) grown coherent AlGaAs/GaAs epitaxic layers have been measured. The composition was calculated both by using theoretical values for the lattice parameters of the limiting compositions together with Vegard's law and also by using an epitaxic layer of AlAs as an in situ standard. The accuracy of this concentration measurement is evaluated by comparing it with an independent measurement of the composition. MBE-grown AlxGa1 − xAs (x = 0.3, 0.5, 0.7) epitaxic layers in the thickness range 0.2–6.0 μm were used to investigate the usefulness of the X-ray rocking-curve method for layer thickness measurement. The experimental rocking curves are compared with those generated from computer simulations based on X-ray dynamical scattering theory. In the thickness range 0.5–2.0 μm Bragg-geometry Pendellösung fringes are also observed. The layer thicknesses calculated from the integrated intensity ratios and the fringe spacings agree with layer thicknesses obtained from scanning electron microscope (SEM) sections. The applicability of this method to multiple layers is investigated using test structures.

Selective Area Deposition of Passivants, Insulators, and Epitaxial Films of II-VI Compound Semiconductors

ABSTRACTII-VI semiconductor surface passivants, insulators, and epitaxial films have been deposited onto selective surface areas by employing a new masking and lift-off technique. The II-VI layers were grown by either conventional or photoassisted molecular beam epitaxy (MBE). CdTe has been selectively deposited onto HgCdTe epitaxial layers as a surface passivant. Selective-area deposition of ZnS has been used in metal-insulator-semiconductor (MIS) structures. Low resistance ohmic contacts to p-type CdTe:As have also been realized through the use of selectively-placed thin films of the semi-metal HgTe followed by a thermal evaporation of In. Epitaxial layers of HgTe, HgCdTe, and HgTe-CdTe superlattices have also been grown in selective areas on CdZnTe substrates, exhibiting specular morphologies and double-crystal x-ray diffraction rocking curves (DCXD) with full widths at half maximum (FWHMs) as narrow as 140 arcseconds.

Effects of Helium Ion Implantation on the Optical and Crystal Properties of GaAs

AbstractThe damage to GaAs crystals caused by helium ion implants has been monitored by changes in the Raman scattering phonon modes, double-crystal x-ray diffraction rocking curves, photoreflectance (PR), and electron beam electroreflectance (EBER) band edge transitions. As the implanted helium ion dose was increased, the various techniques revealed threshold damage behavior at very different levels. Although PR and EBER were the most sensitive to the defects created at the lowest ion doses, all techniques indicated substantial disorder for implants greater than 1014 ions/cm2.

Controlled substitutional doping of CdTe thin films grown by photoassisted molecular-beam epitaxy

We report the successful substitutional doping of CdTe films grown by a new technique: photoassisted molecular-beam epitaxy. This new growth technique gives rise to dramatic changes in the electrical properties of as-grown epilayers, as determined by variable-temperature Hall-effect measurements. In particular, highly conducting n-type and p-type CdTe films have been grown using indium and antimony as n-type and p-type dopants, respectively. Double-crystal x-ray diffraction rocking curve data indicate that the doped epilayers are of high structural quality. Using the photoassisted molecular-beam epitaxy technique, double-layer thin-film CdTe p–n junction diodes have been successfully fabricated for the first time. The application of this new film growth technique to control the electrical properties of another II–VI material has also been demonstrated by the successful n-type doping of CdMnTe epilayers with indium.