High Resolution X-ray Diffraction Scans Research Articles

Impact of composition of AlGaInAs confining barriers on emission of InAs quantum dots embedded in AlGaAs/GaAs dot-in-a-well heterostructures

The emission of InAs quantum dots (QDs) grown on Al0.30 Ga0.70As/GaAs heterostructures and integrated into additional capping/buffer quantum wells (QW), known as dot-in-a-well (DWELL) structures, has been investigated. Two different AlGaInAs confining barriers (CBs) and buffer layers (BLs) are compared. The first QD structure includes the Al0.30 Ga0.70As CB (#1) and the In0.15Ga0.85As BL. The second QD structure consists of the Al0.40Ga0.45In0.15As CB (#2) and the In0.25Ga0.75As BL. Comparison of photoluminescence (PL) spectra has revealed that the ground state (GS) emission band in the structure #2 with Al0.40Ga0.45In0.15As CB is characterized by the lower peak energy, smaller PL linewidth (more homogeneous QD sizes) and higher GS emission intensity compared to that parameters in the structure #1 with Al0.30 Ga0.70As CB. The smaller potential barriers at the Al0.40Ga0.45In0.15As CB/QD interfaces in #2 lead to faster thermal decrease in the GS PL intensity at high temperatures compared with that in #1. High-resolution X-ray diffraction (HR-XRD) method was used for the study of the QD structures with the aim of monitoring the sizes and compositions of QDs and QWs. Numerical simulation of HR-XRD scans has shown that the material compositions of QDs and QW in #2 with Al0.40Ga0.45In0.15As CB has not changed in the process of QD structure growth at high temperatures compared to those in #1. The obtained results are interesting for further improvement of InAs/GaAs QD structures for telecommunication technology and optoelectronic applications.

Optical Properties and HR-XRD Study of /InGaAs/Al Ga As/GaAs Structures with InAs Quantum Dots and Different Capping Layers

The Al0.30Ga0.70As/InGaAs/AlGaInAs/Al0.30Ga0.70As structures with embedded InAs quantum dots (QDs) covered by strain reduced AlGaInAs capping layer have been investigated in as grown state by means of a photoluminescence (PL) and high resolution X ray diffraction (HR-XRD) methods. Two types of QD structures with different quantum well (QW) capping layers: Al0.10In0.15Ga0.75As (#1) and Al0.40In0 .15Ga0.45As (#2) are compared. It is revealed that the QD emission in the structure with Al0.10In0.15Ga0.75As capping is characterized by the highest PL intensity of the ground state (GS) band and smaller the full with at half maximum (FWHM), compared to #2 structures. The variation of the GS emission peak versus temperature has been monitored within the range of 10-400K for the as grown film states and compared with shrinkage of the energy bandgaps in the InAs and GaAs bulk crystals. The results show that the efficiency of Ga/Al/In intermixing in #2 is less than in #1. HR-XRD study has shown that the both QD structures are characterized by best quality of QW interfaces with the high numbers of Pendellösung peaks. The HR-XRD scans were numerically modelled for the analysis of QW layer compositions. The peculiarities of PL spectra of the studied QD structures are analyzed and the advances of studied QD structures have been discussed.

Optical Properties and HR-XRD Study of /InGaAs/Al Ga As/GaAs Structures with InAs Quantum Dots and Different Capping Layers

The Al0.30Ga0.70As /InGaAs/AlGaInAs/ Al0.30Ga0.70As structures with embedded InAs quantum dots (QDs) covered by strain reduced AlGaInAs capping layers have been investigated in an as-grown state using the photoluminescence (PL) and high resolution X ray diffraction (HR-XRD) methods. Two types of QD structures with different quantum well (QW) capping layers: Al0.10In0.15Ga0.75As (#1) and Al0.40In0.15Ga0.45As (#2), and buffer QW layers: In0.15Ga0.85As (#1) and In0.25Ga0.75As (#2) are compared. It is revealed that QD emission in the structure with Al0.10In0.15Ga0.75As capping (#1) is characterized by the higher PL intensity of the ground state (GS) band and smaller the full with at half maximum (FWHM), compared to those in #2. The variation of the GS emission intensity versus temperature has been monitored within the range of 10-500K. It was revealed more significant PL thermal quenching in #1 compared with #2. HR-XRD study has shown that the both QD structures are characterized by the best quality of the QW interfaces with the high numbers of Pendellösung peaks. The analysis of HR-XRD scans permits to estimate the values of the elastic strains in the studied QD structures, which were higher in #2 compared with #1. The peculiarities of PL spectra and HR-XRD are analyzed and the advances of studied QD structures have been compared and discussed.

Epitaxial Ge-on-Nothing Virtual Substrates for 3D Device Stacking Technologies

Future monolithic heterogeneous integration of Ge and IIIV materials in electronic, optoelectronic and photonic devices requires advanced layer transfer and 3D device stacking technologies, which starts with the fabrication of suitable (virtual) substrates. A layer transfer process based on the reorganization of macro-porous Si at high temperature was developed by imec [1]. The developed fabrication scheme to fabricate macropores is based on standard UV lithography and dry etching techniques rather than electrochemical etching. This enables an easy transfer to full Si wafers (up to 300 mm). During a high-temperature step, the top part of the macro-porous Si reflows. By using proper anneal conditions, the layer detaches from the mother substrate, being anchored by a few attachment points only, forming a ‘Si on nothing’ (SoN) stack (Fig. 1a). The suspended Si layer can then easily be transferred to another substrate.In this contribution, we assess the suitability of macro-porous Si and SoN as starting material for Ge virtual substrates. The goal is to provide a fabrication scheme that allows an easy detachment of the virtual substrate after wafer to wafer bonding. Macro-porous Si was only fabricated in the inner 10x10 cm2 area of 200 mm wafers using imec’s qualified fabrication scheme. Ge layers were simultaneously grown on the inner macro-porous Si (or SoN) and the outer bulk Si. This allows to compare the material properties without the risk of wafer to wafer variations due to non-reproducibility issues. Our approach for making macro-porous Si and SoN provides mono-crystalline, nearly defect-free, and extremely smooth Si starting surfaces. A standard low temperature epitaxial Ge growth process in an ASM-Epsilon® 2000 system was used to deposit the Ge layers [2].As an example, Fig. 1b shows a 1.25 mm thick mono-crystalline epitaxial Ge layer grown on a macro-porous Si layer. The Ge growth proceeds in a 2-dimensional mono-crystalline growth mode. The surface morphology of the grown Ge is not affected by the starting surface (Fig. 1c,d). The Full Width at Half Maximum (FWHM) as extracted from w-2q High Resolution X-ray Diffraction scans acquired around the Ge (004) Bragg peak is strongly reduced after a post Ge deposition anneal, which was also reported for Ge on bulk Si [2]. Threading dislocations annihilate during the post-epi anneal. FWHM values as low as 160 arc sec have been measured for 1.25 mm thick Ge layers independent of the underlying layer. This reflects the high material quality of the grown Ge. The difference in thermal expansion coefficient between Si and Ge results in some tensile stress in the annealed Ge layer, which explains the well-known shift in XRD peak position. The improvement in material quality by using a post-epi anneal is also reflected in the carrier lifetime as extracted from room-temperature photoluminescence measurements. The carrier lifetime increases from <0.2 ns (as-grown layers) to 3.3 ns and 3.6 ns for Ge on porous Si and bulk Si, respectively. The TDD, as extracted from ECCI measurements, was identical for both parts of the Si wafer (2-4e7 cm-2) and close to the values expected from literature. The material properties listed above are not affected by the thickness of the closed Si layer in-between the Ge and the porous Si.In conclusion, we developed a fabrication scheme for strain-relaxed Ge grown on SoN (or on macroporous Si) starting from conventional Si substrates. The material properties of the virtual Ge substrate are identical to those obtained for Ge grown on bulk Si. The virtual substrate serves as starting material for layer transfer and 3D device stacking technologies. The fabrication scheme can be extended to (defect free) bulk Ge for which the fabrication of Ge on nothing followed by layer transfer has been demonstrated [3].

Quantitative determination of short-range order in magnetostrictive Fe-12.5 at. % Ga alloy single crystals

FeGa alloys are an important class of magnetostrictive materials for use in actuators and sensors. Quantitative determination of short-range order is critical for a fundamental understanding of the correlation of thermal history with magnetostriction in these and other α-Fe based alloys. This paper presents quantitative assessments of short-range order (SRO) from the diffuse peaks in the high-resolution x-ray diffraction scan data of as-grown and high-temperature annealed Fe-12.5 at. % Ga alloy single crystals. The peak analyzed was the diffuse peak in the forbidden (100) peak region of the diffraction pattern of bcc Fe-12.5 at. % Ga alloy single crystals. The [001]-oriented Fe-12.5 at. % Ga alloy single crystals were obtained using the vertical Bridgman technique. To quantitatively assess SRO in these alloy single crystals, the x-ray scattering intensities obtained were converted to absolute intensity in electron scattering units. To do this, reference scans were performed on a fully dense polystyrene sample. A Python language based code was used for the analysis of short-range order, and the values for the SRO coefficients up to the seventh shell were determined. These values agree with the type of ordering indicated by (111) scans of these crystals.

Emission and HR-XRD varying in GaAs/AlGaInAs heterostructures with InAs quantum dots at annealing

GaAs/Al0.30Ga0.70As/AlGaInAs/ heterostructures grown by molecular beam epitaxy with embedded InAs quantum dots (QDs) have been investigated before and after thermal annealing at 640 °C for 2 h. Two types of QD structures with the different compositions of capping layers: (Al0.30Ga0.70As (#1) and Al0.10Ga0.75In0.15As (#2)), are studied using the photoluminescence (PL), X-ray diffraction (XRD) and high-resolution XRD (HR-XRD) techniques. The high PL intensity, smaller half width of PL bands and lower energy of the ground state (GS) emission are detected in the structure with the Al0.10Ga0.75In0.15As capping layer. The blue shift of PL spectra is detected after annealing and this shift is more significant in the structure with Al0.10Ga0.75In0.15As capping as well. The last effect has been explained by the efficient Ga/In inter-diffusion at the AlGaInAs/InAs QD interface in #2 owing to the smaller In-As binding energy in comparison with Al-As and Ga-As ones in the studied alloy. The composition variation of the QDs and quantum wells (QWs) due to Ga/In intermixing at annealing has been modeled on the base of the numerical simulation of HR-XRD scans with the help of X′ Pert Epitaxy software.

Emission and HR-XRD study of MBE structures with InAs quantum dots and AlGaInAs strain reducing layers

GaAs/Al0.30Ga0.70As quantum wells (QWs) with InAs quantum dot (QD) arrays covered by the different capping layers: Al0.30Ga0.70As or Al0.1Ga0.75In0.15As, have been investigated by means of the photoluminescence (PL) and high resolution X-ray diffraction (HR-XRD) methods. It is revealed that the QD emission in the structure with Al0.1Ga0.75In0.15As capping is characterized by the lower PL energy, higher PL intensity of ground state emission and smaller its full width at half maximum (FWHM) in comparison with ground state QD emission at Al0.30Ga0.70As capping. The analysis of PL and HR-XRD scans has shown that the strain relaxation at high QW growth temperatures in the structure with Al0.30Ga0.70As capping was connected with changing significantly the material compositions of the QDs and capping layer. As a result the QD emission shifts into the higher energy range, the PL intensity decreases and the FWHMs of PL bands increase. In contrary, in the structure with Al0.1Ga0.75In0.15As capping the strain relaxation manifests itself by decreasing the InAs QD heights without changing the InAs QD material composition. The advantage of Al0.1Ga0.75In0.15As capping has been discussed.

Evaluation of threading dislocation density of strained Ge epitaxial layer by high resolution x-ray diffraction**Project supported by the Research Plan in Shaanxi Province, China (Grant No. 2016GY-085), the Opening Project of Key Laboratory of Microelectronic Devices & Integrated Technology, Institute of Microelectronics, Chinese Academy of Sciences (Grant No. 90109162905), the Fundamental Research Funds for the Central Universities (Grant No. 17-H863-04-ZT-001-019-01),

The analysis of threading dislocation density (TDD) in Ge-on-Si layer is critical for developing lasers, light emitting diodes (LEDs), photodetectors (PDs), modulators, waveguides, metal oxide semiconductor field effect transistors (MOSFETs), and also the integration of Si-based monolithic photonics. The TDD of Ge epitaxial layer is analyzed by etching or transmission electron microscope (TEM). However, high-resolution x-ray diffraction (HR-XRD) rocking curve provides an optional method to analyze the TDD in Ge layer. The theory model of TDD measurement from rocking curves was first used in zinc-blende semiconductors. In this paper, this method is extended to the case of strained Ge-on-Si layers. The HR-XRD scan is measured and Ge (004) single crystal rocking curve is utilized to calculate the TDD in strained Ge epitaxial layer. The rocking curve full width at half maximum (FWHM) broadening by incident beam divergence of the instrument, crystal size, and curvature of the crystal specimen is subtracted. The TDDs of samples A and B are calculated to be 1.41 × 108 cm−2 and 6.47 × 108 cm−2, respectively. In addition, we believe the TDDs calculated by this method to be the averaged dislocation density in the Ge epitaxial layer.

Band gap bowing parameter in pseudomorphic AlxGa1−xN/GaN high electron mobility transistor structures

A method for evaluation of aluminium composition in pseudomorphic AlxGa1−xN layer from the measured photoluminescence (PL) peak energy is presented here. The layers were grown by metalorganic chemical vapor deposition and characterized by high resolution X-ray diffraction (HRXRD), PL, cathodoluminescence, and atomic force microscopy. We estimated the value of biaxial stress in pseudomorphic AlxGa1−xN layers grown on sapphire and silicon carbide substrates using HRXRD scans. The effect of biaxial stress on the room temperature band edge luminescence in pseudomorphic AlxGa1−xN/GaN layers for various aluminium compositions in the range of 0.2 &amp;lt; x &amp;lt; 0.3 was determined. The value of pressure coefficient of band gap was also estimated. The stress corrected bowing parameter in AlxGa1−xN was determined as 0.50 ± 0.06 eV. Our values match well with the theoretically obtained value of bowing parameter from the density functional theory.

Comprehensive strain and band gap analysis of PA-MBE grown AlGaN/GaN heterostructures on sapphire with ultra thin buffer

In this work, cluster tool (CT) Plasma Assisted Molecular Beam Epitaxy (PA-MBE) grown AlGaN/GaN heterostructure on c-plane (0 0 0 1) sapphire (Al2O3) were investigated by High Resolution X-ray Diffraction (HRXRD), Room Temperature Raman Spectroscopy (RTRS), and Room Temperature Photoluminescence (RTPL). The effects of strain and doping on GaN and AlGaN layers were investigated thoroughly. The out-of-plane (‘c’) and in-plane (‘a’) lattice parameters were measured from RTRS analysis and as well as reciprocal space mapping (RSM) from HRXRD scan of (002) and (105) plane. The in-plane (out-of plane) strain of the samples were found to be −2.5 × 10−3(1 × 10−3), and −1.7 × 10−3(2 × 10−3) in GaN layer and 5.1 × 10−3 (−3.3 × 10−3), and 8.8 × 10−3(−1.3 × 10−3) in AlGaN layer, respectively. In addition, the band structures of AlGaN/GaN interface were estimated by both theoretical (based on elastic theory) and experimental observations of the RTPL spectrum.

Epitaxial growth of large area single-crystalline few-layer MoS2 with high space charge mobility of 192 cm2 V−1 s−1

We report on the vapor-solid growth of single crystalline few-layer MoS2 films on (0001)-oriented sapphire with excellent structural and electrical properties over centimeter length scale. High-resolution X-ray diffraction scans indicated that the films had good out-of-plane ordering and epitaxial registry. A carrier density of ∼2 × 1011 cm−2 and a room temperature mobility of 192 cm2/Vs were extracted from space-charge limited transport regime in the films. The electron mobility was found to exhibit in-plane anisotropy with a ratio of ∼1.8. Theoretical estimates of the temperature-dependent electron mobility including optical phonon, acoustic deformation potential, and remote ionized impurity scattering were found to satisfactorily match the measured data. The synthesis approach reported here demonstrates the feasibility of device quality few-layer MoS2 films with excellent uniformity and high quality.

Structural and optical properties of AlxGa1−xN/GaN high electron mobility transistor structures grown on 200 mm diameter Si(111) substrates

The authors report on the study of homogeneity in structural and optical properties of AlxGa1−xN/GaN high electron mobility transistor (HEMT) structures grown on 200 mm diameter Si(111) substrates. The consequence of a variation of buffer layer thicknesses as well as the interface quality has been studied by in-situ growth monitoring. A reasonably good uniformity of crystalline quality in the heterostructures grown with a lower wafer bowing has been observed from the full width at half maxima of symmetric as well as asymmetric high resolution x-ray diffraction scans across the wafer. Furthermore, the thickness and Al content of the AlxGa1−xN barrier layer across the wafer is found to be uniform when the wafer bowing is lower. Optical and electrical measurements across the epiwafer address the strain homogeneity, luminescence, and two-dimensional electron gas properties. Based on these studies of growth optimization, HEMT epiwafers with a total nitride stack thickness of 4.4 μm with a wafer bowing &amp;lt;50 μm on 1.0 mm thick Si substrates are demonstrated.

Migration-enhanced epitaxy of thin GaAsBi layers

Thin GaAsBi layers and bismide-based multiple quantum structures were grown by migration-enhanced epitaxy onto GaAs(100) substrates at 140–240 °C temperatures. The Bi content in GaAs, evaluated from high-resolution X-ray diffraction scans, varied from 2.5 to 10.3% depending on growth temperature, Bi and As atomic ratio as well as on the sequence of Ga, Bi, and As molecular supplies. The atomic force microscopy revealed a tendency of smoothening of the GaAsBi surface with substrate temperature decreasing. Transmission electron microscopy investigations evidenced high crystalline material quality of GaAsBi quantum wells and GaAs barriers.

Migration-enhanced epitaxy of thin GaAsBi layers

Thin GaAsBi layers and bismide-based multiple quantum structures were grown by migration-enhanced epitaxy onto GaAs(100) substrates at 140–240 °C temperatures. The Bi content in GaAs, evaluated from high-resolution X-ray diffraction scans, varied from 2.5 to 10.3% depending on growth temperature, Bi and As atomic ratio as well as on the sequence of Ga, Bi, and As molecular supplies. The atomic force microscopy revealed a tendency of smoothening of the GaAsBi surface with substrate temperature decreasing. Transmission electron microscopy investigations evidenced high crystalline material quality of GaAsBi quantum wells and GaAs barriers.

Modified statistical dynamical diffraction theory: analysis of model SiGe heterostructures

A modified version of the statistical dynamical diffraction theory (mSDDT) permits full-pattern fitting of high-resolution X-ray diffraction scans from thin-film systems across the entire range from fully dynamic to fully kinematic scattering. The mSDDT analysis has been applied to a set of model SiGe/Si thin-film samples in order to define the capabilities of this approach. For defect-free materials that diffract at the dynamic limit, mSDDT analyses return structural information that is consistent with commercial dynamical diffraction simulation software. As defect levels increase and the diffraction characteristics shift towards the kinematic limit, the mSDDT provides new insights into the structural characteristics of these materials.

The Formation of New Periodicities after N-Implantation in 4H- and 6H-SiC Samples

The purpose of the present study is to study the crystal periodicities that appear in 4H- and 6H-SiC material after the implantation with nitrogen and prior to post-implantation annealing. High Resolution X-Ray diffraction (HRXRD) and Transmission Electron Microscopy (TEM) have been employed towards this purpose. Extra peaks at smaller, than the main (00n) peak, diffraction angles in HRXRD scans and extra spots in the electron diffraction patterns have been observed due to the presence of these periodicities. Higher lattice constant periodic structures are apparently formed from the implanted nitrogen ions located at interstitial sites and disappear after the annealing and the resulting positioning of nitrogen atoms in substitutional sites.

2.8 μm emission from type-I quantum wells grown on InAsxP1−x/InP metamorphic graded buffers

We report 2.8 μm emission from compressively strained type-I quantum wells (QWs) grown on InP-based metamorphic InAsxP1−x step-graded buffers. High quality metamorphic graded buffers showed smooth surface morphology and low threading dislocation densities of approximately 2.5 × 106 cm−2. High-resolution x-ray diffraction scans showed strong satellites from multiple quantum wells grown on metamorphic buffers, and cross-sectional transmission electron microscopy revealed smooth and coherent quantum well interfaces. Room-temperature photoluminescence emission at 2.8 μm with a narrow linewidth (∼50 meV) shows the promise of metamorphic growth for mid-infrared laser diodes on InP.

High compositional homogeneity in In-rich InGaAs nanowire arrays on nanoimprinted SiO2/Si (111)

We report improved homogeneity control of composition-tuned In1−xGaxAs (x < 0.4) nanowire (NW) arrays grown by catalyst-free molecular beam epitaxy (MBE) on nanoimprinted SiO2/Si (111) substrates. Using very high As/(Ga+In) ratios at growth temperatures of 550 °C enabled uniform incorporation of the respective group-III elements (In,Ga) over the investigated composition range, confirmed by high-resolution x-ray diffraction (HRXRD) and energy dispersive x-ray spectroscopy. Low-temperature (20 K) photoluminescence of these In-rich In1−xGaxAs NW ensembles reveal state-of-the-art linewidths of ∼29–33 meV. These are independent of Ga content, suggesting an overall low degree of phase separation. In contrast, self-assembled, non-periodic In1−xGaxAs NW arrays show larger inhomogeneity with increased peakwidths in 2θ−ω HRXRD scans as well as broadened Raman modes. These results demonstrate the excellent potential of site-selective MBE growth of high-periodicity non-tapered In1−xGaxAs NW arrays with low size and composition dispersion for optimized device integration on Si.

Observation of columnar microstructure in lattice-matched InAlN/GaN grown by plasma assisted molecular beam epitaxy

Nominally lattice matched InAlN/GaN was grown by plasma-assisted molecular beam epitaxy, and the intrinsic microstructure was investigated via x-ray diffraction, transmission electron microscopy, and atom probe tomography. The InAlN showed a cellular structure, which was comprised of ∼10 nm wide Al-rich cores and ∼1 nm In-rich InAlN intercellular boundaries. Despite the strong laterally non-uniform In distribution, both vertical and lateral lattices are unperturbed by the cellular structure, as evidenced by strong thickness fringes in on-axis ω−2θ high resolution x-ray diffraction scans, coherence lengths derived from on-axis (0002) and off-axis (101¯2) ω−2θ high resolution x-ray diffraction scans, and a modified Williamson-Hall analysis for on-axis reflections.

Molecular beam epitaxial growth and characterization of InSb1 − xNx on GaAs for long wavelength infrared applications

Recent research progress and findings in InSbN have attracted great attention due to its use in long wavelength infrared applications. A large bandgap reduction in InSb resulting from high N incorporation with minimal crystal defects is challenging due to relatively small atomic size of N. Hence optimization of growth conditions plays an important role in the growth of high-quality InSbN epilayers for device purposes. In this paper, we report on the correlation of structural, vibrational, electrical, and optical properties of molecular beam epitaxially grown InSbN epilayers grown on GaAs substrates, as a function of varying growth temperatures. Two dimensional growths of InSb and InSbN were confirmed from dynamic reflection high energy electron diffraction patterns and growth parameters were optimized. High crystalline quality of the epilayers is attested to by a low full width at half maximum of 200 arcsec from high resolution x-ray diffraction (HRXRD) scans and by the high intensity and well-resolved InSb longitudinal optical (LO) and 2nd order InSb LO mode observed from micro-Raman spectroscopy. The N incorporation in these InSbN epilayers is estimated to be 1.4% based on HRXRD simulation. X-ray photoelectron spectroscopy (XPS) studies reveal that most of the N present in the layers are in the form of In-N bonding. Variation of the lattice disorder with growth temperature is correlated with the types of N bonding present, the carrier concentration and mobility, observed in the corresponding XPS spectra and Hall measurements, respectively. XPS analysis, HRXRD scans, and Raman spectral analysis indicate that lower growth temperature favors In-N bonding which dictates N incorporation in the substitutional sites and lattice disorder, whereas, high growth temperature promotes the formation of In-N-Sb bonding. The best room temperature and 77 K electrical transport parameters and maximum redshift in the absorption edge have been achieved in the InSbN epilayer grown in the 290 °C ∼ 330 °C temperature range.