High-resolution X-ray Diffraction Results Research Articles

XRD and photoluminescence measurements of GaN grown on dome shaped patterned sapphire with different NH3 flow rates

The aim of the study is to understand the effects of NH3 flow rate in the initial part of high temperature (HT) GaN growth on structural and optical characteristics of the HT-GaN layer grown on dome shaped sapphire susbtrate by Metal Organic Chemical Vapor Deposition (MOCVD) system. High resolution x-ray diffraction (HRXRD) and photoluminescence (PL) measurements were performed to characterization the growing GaN epilayer. It is observed that the using of different NH3 flow rate in the initial part of HT-GaN growth has an effect on both full-width at half-maximum (FWHM) values obtained from HRXRD results and intensities of yellow luminescence peaks. It is seen that the FWHM values obtained from the symmetric (00.2) omega scan increased as the NH3 flow rates in the initial part of HT-GaN growth increased. It is demonstrated that the intensities of yellow luminescence peaks are very sensitive to NH3 flow rates in the initial part of HT-GaN growth.

Optimization of vertical strain coupling in InAs/GaAs p-i-p quantum dot infrared photodetectors with applied growth strategy

The authors report the optimization of vertically coupled active layers of InAs quantum dots (QDs) grown epitaxially following a unique in-situ growth strategy to achieve controlled strain propagation in subsequent layers resulting in homogenous dot-size distribution. The analysis comprises of bi, tri, penta, hepta and deca coupled layers which have been characterized for their optical properties using photoluminescence spectroscopy (PL) and photoluminescence excitation spectroscopy measurements (PLE) while high resolution X-ray diffraction (HR-XRD) measurements (in-plane and out-of-plane) have been carried out for structural characterization. A gradual shift from bi-modal to monomodal distribution is observed on increasing the coupled layers above five. Activation energies (Ea) calculated from temperature dependent PL results show least thermal quenching for hepta layer coupling which is further corroborated by the strongest room temperature luminescence obtained for the respective sample amongst others. Least out-of-plane compressive strain and also least in-plane tensile strain have been calculated from the HR-XRD results for the hepta layer coupled sample. Furthermore, the in-plane HR-XRD results show minimal amount of In–Ga intermixing for the hepta layer coupling which provides direct evidence of the superior material quality of this heterostructure. Quantum-dot infrared photodetectors (QDIPs) fabricated from the samples have been characterized for their spectral response wherein multiple sharp peaks with narrow full-width at half maxima (FWHM) are obtained in the short-wave infrared (SWIR) region for the hepta layer device, which is absent in other spectra. Also, the response survives up to room temperature (300 K) and stretches in the mid-wave infrared region (MWIR) region (~5 μm). High peak responsivity (Rp = 120.34 A/W) is obtained for the hepta layer device which is much higher than previously reported responsivity values.

Microstructure and temperature-dependence of Raman scattering properties of β-(AlxGa1-x)2O3 crystals

Abstract Bulk crystals of β-Ga2O3, (Al0.1Ga0.9)2O3 and (Al0.2Ga0.8)2O3 were grown by the optical floating zone and edge-defined film-fed methods. Their microstructure and temperature-dependent phonon characteristics were investigated systematically by using high resolution X-ray diffraction (HR-XRD) and Raman scattering spectroscopy. HR-XRD results revealed a very good crystalline phase for all the samples. As compared to the pure β-Ga2O3, the interplanar spacings in (Al0.1Ga0.9)2O3 and (Al0.2Ga0.8)2O3 samples are found decreasing with the increase of Al contents – exhibiting distorted lattice structures. Due to the deformations in (AlxGa1-x)2O3, the Raman peaks revealed redshifts and linewidth broadening as the Al composition (x) is increased. The lattice distortion mainly affected the Raman modes in the range of less than 600 cm−1 and had a relatively trivial effect on the modes higher than 600 cm−1. With the increase of temperature, the Raman peaks are also redshifted and linewidth broadened. Similar to a pure β-Ga2O3, our Raman shifts in the two (AlxGa1-x)2O3 crystals revealed quadratic dependence on temperature – showing specific relationships. However, the temperature dependent widening of the Raman active phonons in (AlxGa1-x)2O3 exhibited a convoluted behavior different from β-Ga2O3. The results are significant for further understanding of (AlxGa1-x)2O3 crystals and evaluating its use in device applications.

Thickness dependence of crystal and optical characterization on ZnO thin film grown by atomic layer deposition

We studied the thickness dependence of the crystallographic and optical properties of ZnO thin films grown on c-plane sapphire substrate using atomic layer deposition. High-resolution X-ray diffraction (HR-XRD) revealed two peaks at 34.5° and 36.2° in the initial growth stage of ZnO on the sapphire substrate, corresponding to the (002) and (101) ZnO planes, respectively. However, as the thickness of the ZnO film increased, the XRD intensity of the (002) ZnO peak increased drastically, compared with that of the (101) ZnO peak. This indicated that (002) and (101) ZnO were simultaneously grown on the c-plane sapphire substrate in the initial growth stage, and that (002) ZnO was predominantly grown with the increase in the thickness of ZnO film. The ZnO thin film presented an anisotropic surface structure at the initial stage, whereas the isotropic surface morphology was developed with an increase in the film thickness of ZnO. These observations were consistent with the HR-XRD results.

Influence of in-situ deposited SiNx interlayer on crystal quality of GaN epitaxial films

GaN epitaxial films with SiNx interlayers were prepared by metal organic chemical vapor deposition (MOCVD) on c-plane sapphire substrates. The influences of deposition times and locations of SiNx interlayers on crystal quality of GaN epitaxial films were studied. Under the optimal growth time of 120 s for the SiNx interlayer, the dislocation density of GaN film is reduced to 4.05 × 108 cm−2 proved by high resolution X-ray diffraction results. It is found that when the SiNx interlayer deposits on the GaN nucleation islands, the subsequent GaN film has the lowest dislocation density of only 2.89 × 108 cm−2. Moreover, a model is proposed to illustrate the morphological evolution and associated propagation processes of TDs in GaN epi-layers with SiNx interlayers for different deposition times and locations.

Interfacial relaxation analysis of InGaAs/GaAsP strain-compensated multiple quantum wells and its optical property

InGaAs/GaAsP strain-compensated multiple quantum wells were prepared by metal organic chemical vapor deposition on GaAs (100) substrates with misorientation of 15° toward [111]. In order to obtain better strain-compensated abrupt heterojunction interfaces, the compressive strain and relaxation of different quantum well and the total accumulated strain were investigated by adjusting In composition and the thickness of InxGa1-xAs well and GaAs1-yPy barrier keep constant. High resolution X-ray diffraction results indicate the crystal and interfacial structures of In0.18Ga0.82As (7 nm)/GaAs1-yPy with the least relaxation and total strain mismatch are better than others. From in-situ surface reflectivity curves, we observed the slope of reflectivity curve of multiple quantum wells increases with increasing lattice relaxation. Atomic force microscopic results show surface morphologies of three samples are Volmer-Weber mode. Indium segregation at heterointerface between well and barrier were investigated by secondary ion mass spectrometry which indicate indium diffusion width increase with the increasing total strain mismatch. Finally, a shoulder peak was observed from Gaussian fitting of photoluminescence, stemming from the lattice relaxation. These results demonstrate that the relaxation process is introduced and indium segregation length widens as the relaxation increases. The experimental results will be favorable for optimizing the epitaxial growth of InGaAs/GaAsP strain-compensated quantum wells in order to obtain high quality smooth heterointerface.

Structural, optical and electrical characterization of dilute nitride GaP1−x−yAsyNx structures grown on Si and GaP substrates

The structural, optical and electrical properties of dilute nitride p–n junction GaP1−x−yAsyNx structures grown on n-type GaP (100) and n-type Si (100) misoriented by 4° towards the [110] direction substrates were studied. These properties of the samples, which were grown by using molecular beam epitaxy (MBE) technique, were investigated by using high-resolution X-Ray diffraction (HRXRD), energy dispersive X-Ray (EDX), room temperature photoluminescence (PL) and current–voltage (I–V) measurements. Both alloy composition values (x, y) and crystal structure parameters were determined from HRXRD measurements while the band gap energies were obtained from PL measurements. Composition values were also determined by using EDX measurements and compared with HRXRD results. The better crystal quality was found for the sample grown on GaP substrate from both the HRXRD and PL results. In addition, the theoretical band gap energies calculated from the band anticrossing (BAC) model and experimental band gap energies determined from the PL measurements were compared and found to be in good agreement with each other. The p–n junction GaP1−x−yAsyNx/GaP (Si) diode devices were fabricated to investigate their electrical properties. The I–V characteristics of diodes were analyzed at room temperature and the diode formed on GaP substrate exhibited better results compared to other diode.

Quantitative analysis of the interplay between InAs quantum dots and wetting layer during the GaAs capping process

A procedure to quantitatively analyse the relationship between the wetting layer (WL) and the quantum dots (QDs) as a whole in a statistical way is proposed. As we will show in the manuscript, it allows determining, not only the proportion of deposited InAs held in the WL, but also the average In content inside the QDs. First, the amount of InAs deposited is measured for calibration in three different WL structures without QDs by two methodologies: strain mappings in high-resolution transmission electron microscopy images and compositional mappings with ChemiSTEM x-ray energy spectrometry. The area under the average profiles obtained by both methodologies emerges as the best parameter to quantify the amount of InAs in the WL, in agreement with high-resolution x-ray diffraction results. Second, the effect of three different GaAs capping layer (CL) growth rates on the decomposition of the QDs is evaluated. The CL growth rate has a strong influence on the QD volume as well as the WL characteristics. Slower CL growth rates produce an In enrichment of the WL if compared to faster ones, together with a diminution of the QD height. In addition, assuming that the QD density does not change with the different CL growth rates, an estimation of the average In content inside the QDs is given. The high Ga/In intermixing during the decomposition of buried QDs does not only trigger a reduction of the QD height, but above all, a higher impoverishment of the In content inside the QDs, therefore modifying the two most important parameters that determine the optical properties of these structures.

Advantages of InGaN/GaN multiple quantum wells with two-step grown low temperature GaN cap layers

Two-step grown low temperature GaN cap layers (LT-cap) are employed to improve the optical and structural properties of InGaN/GaN multiple quantum wells (MQWs). The first LT-cap layer is grown in nitrogen atmosphere, while a small hydrogen flow is added to the carrier gas during the growth of the second LT-cap layer. High-resolution X-ray diffraction results indicate that the two-step growth method can improve the interface quality of MQWs. Room temperature photoluminescence (PL) tests show about two-fold enhancement in integrated PL intensity, only 25 meV blue-shift in peak energy and almost unchanged line width. On the basis of temperature-dependent PL characteristics analysis, it is concluded that the first and the second LT-cap layer play a different role during the growth of MQWs. The first LT-cap layer acts as a protective layer, which protects quantum well from serious indium loss and interface roughening resulting from the hydrogen over-etching. The hydrogen gas employed in the second LT-cap layer is in favor of reducing defect density and indium segregation. Consequently, interface/surface and optical properties are improved by adopting the two-step growth method.

Effect of small flow hydrogen treatment at the upper well/barrier interface on the properties of InGaN/GaN multiple quantum wells

To enhance the quality of InGaN/GaN multiple quantum wells (MQWs), a small hydrogen flow is introduced to treat the upper well/barrier interface. High-resolution X-ray diffraction results indicate that hydrogen treatment improves the interface quality of MQWs. Room temperature photoluminescence (PL) tests show that integrated PL intensity is enhanced by 57.6% and line width is narrowed, while emission peak energy is almost unchanged. On the basis of temperature-dependent PL characteristics analysis, it is concluded that hydrogen treatment decreases non-radiative recombination centers in active region, yet has little impact on carrier localization. Moreover, surface roughness and V-pit density are significantly reduced after hydrogen treatment as revealed by atomic force microscopy. Because the emission energy is quite stable after the hydrogen treatment, this method can also be promoted to improve the quality of green and yellow-green emission MQWs.

Bulk Crystal Growth, and High-Resolution X-ray Diffraction Results of LiZnAs Semiconductor Material

LiZnAs is being explored as a candidate for solid-state neutron detectors. The compact form, solid-state device would have greater efficiency than present day gas-filled 3He and 10BF3 detectors. Devices fabricated from LiZnAs having either natural Li (nominally 7.5% 6Li) or enriched 6Li (usually 95% 6Li) as constituent atoms may provide a material for compact high efficiency neutron detectors. The 6Li(n,t)4He reaction yields a total Q-value of 4.78 MeV, an energy larger than that of the 10B reaction, which can easily be identified above background radiations. LiZnAs material was synthesized by preparing equimolar portions of Li, Zn, and As sealed under vacuum (10−6 Torr) in quartz ampoules lined with boron nitride and subsequently reacted in a compounding furnace (Montag et al. in J Cryst Growth 412:103, 2015). The raw synthesized LiZnAs was purified by a static vacuum sublimation in quartz (Montag et al. in J Cryst Growth 438:99, 2016). Bulk crystalline LiZnAs ingots were grown from the purified material with a high-temperature Bridgman-style growth process described here. One of the largest LiZnAs ingots harvested was 9.6 mm in diameter and 4.2 mm in length. Samples were harvested from the ingot and were characterized for crystallinity using a Bruker AXS Inc. D8 AXS Inc. D2 CRYSO, energy dispersive x-ray diffractometer, and a Bruker AXS Inc. D8 DISCOVER, high-resolution x-ray diffractometer equipped with molybdenum radiation, Gobel mirror, four bounce germanium monochromator and a scintillation detector. The primary beam divergence was determined to be 0.004°, using a single crystal Si standard. The x-ray based characterization revealed that the samples nucleated in the (110) direction and a high-resolution open detector rocking curve recorded on the (220) LiZnAs yielded a full width at half maximum (FWHM) of 0.235°. Sectional pole figures using off-axis reflections of the (211) LiZnAs confirmed in-plane ordering, and also indicated the presence of multiple domains. The LiZnAs bulk crystals exhibited a Primitive Cubic Bravais lattice instead of the commonly reported Face-centered Cubic Bravais lattice. The lattice constant was determined to be 5.5146 ± 0.0003 A.

Effect of growth temperature on InGaN/GaN heterostructures grown by MOCVD

InGaN/GaN heterostructured samples were grown at different temperatures varying from 680°C to 760°C on c-plane sapphire substrates using a horizontal flow Metal Organic Chemical Vapor Deposition (MOCVD) reactor. Systematic investigation of structural, optical, morphological and electrical properties has been carried out using High Resolution X-Ray Diffraction (HRXRD), Photoluminescence (PL), Atomic Force Microscope (AFM) and Hall Measurement respectively. From the HRXRD results, the respective Indium (In) composition in the InGaN/GaN heterostructures can be calculated using InGaN (0002) peaks. In incorporation is very much sensitive to the temperature and incorporation of In in InGaN epilayer was found to decrease with increase in growth temperature. PL spectra reveal a shift towards higher energy side because of In incorporation with increasing reactor temperature. AFM images of the sample grown at 680°C shows the In rich clusters due to compositional inhomogeneity. With further increase in the growth temperature, decomposition of InN starts and hence decreases the surface roughness. Hall Effect studies confirm that with increasing growth temperature bulk electron concentration of the InGaN thin films decrease and mobility increases. Maximum bulk electron concentration of ~4.5×1019cm−3 and a mobility of ~295cm2/V-s was obtained for 19% of In. Efforts are being made to optimize the incorporation of In content in InGaN/GaN heterostructures for photovoltaic application.

Characterization and thermal stability of GeSn/Ge multi-quantum wells on Ge (100) substrates

High-quality, high-Sn-content GeSn/Ge multi-quantum well (MQW) structures were grown on Ge (100) substrates by molecular beam epitaxy. The Sn content of the GeSn layers in the MQWs was 7.85 %. High crystalline quality and smooth interfaces were observed by high-resolution X-ray diffraction (HRXRD) and transmission electron microscopy (TEM). Clear multistage satellite peaks were identifiable in the HRXRD results and were consistent with those obtained in simulations. No threading or misfit dislocations were observed in the TEM images. The room temperature photoluminescence showed an enhanced emission peak of direct transitions around 2025 nm due to the quantum confinement effect. Rapid thermal annealing was also performed and indicated that the MQW structures remained stable when annealed at 400 °C for 30 s. With increasing temperature, the intermixing of the GeSn and Ge layers increased, and the structure completely degenerated at 600 °C. These results will provide a valuable reference for the processing of GeSn devices.

Bulk crystal growth, and high-resolution x-ray diffraction results of LiZnP semiconductor material

Nowotny–Juza compounds continue to be explored as a candidate for solid-state neutron detectors. Such a device would have greater efficiency, in a compact form, than present day gas-filled 3He and 10BF3 detectors. The 6Li(n,t)4He reaction yields a total Q-value of 4.78MeV, larger than 10B, an energy easily identified above background radiations. Hence, devices fabricated from semiconducting compounds containing either natural Li (nominally 7.5% 6Li) or enriched 6Li (usually 95% 6Li) may provide a semiconductor material for compact high efficiency neutron detectors. Starting material was synthesized by preparing equimolar portions of Li, Zn, and P sealed under vacuum (10−6Torr) in quartz ampoules lined with boron nitride and subsequently reacted in a compounding furnace [1]. The synthesized material showed signs of high impurity levels from material and electrical property characterizations. A static vacuum sublimation in quartz was performed to help purify the synthesized material [2]. Bulk crystalline samples were grown from the purified material. An ingot 9.6mm in diameter and 4.0mm in length was harvested. Individual samples were characterized for crystallinity on a Bruker AXS Inc. D2 CRYSO, energy dispersive x-ray diffractometer, and a Bruker AXS D8 DISCOVER, high-resolution x-ray diffractometer with a 0.004° beam divergence. The (220) orientation was characterized as the main orientation with the D2 CRYSO, and confirmed with the D8 DISCOVER. An out-of-plane high-resolution rocking curve yielded a 0.417° full width at half maximum (FWHM) for the (220) LiZnP. In-plane ordering was confirmed by observation of the (311) orientation, where a rocking curve was collected with a FWHM of 0.294°.

Domain matching epitaxy of GaN films on a novel langasite substrate: an in-plane epitaxial relationship analysis

We report the epitaxial growth of c-plane GaN films on a novel langasite (La3Ga5SiO14, LGS) substrate by plasma-assisted molecular beam epitaxy. The in-plane epitaxial relationship and the structural properties of GaN films on an LGS substrate were investigated using in situ reflective high energy electron diffraction (RHEED), high resolution X-ray diffraction (HR-XRD) and Raman spectroscopy. The in-plane epitaxial relationship between GaN and LGS determined using RHEED pattern was found to be GaN[100]//LGS[210] and GaN[110]//LGS[140]. HR-XRD results confirmed the exact epitaxial relationship, and showed that six reflection peaks of GaN(102) were shifted around 19° from those of LGS(102). Raman analysis revealed that a minute compressive strain still existed in the GaN film due to the very small lattice mismatch between GaN and LGS. The results obtained in this study demonstrate that the nearly lattice-matched LGS can be a promising and futuristic substrate material for the growth of GaN, and it is foreseen that our results could be a reference for the further development of high performance nitride-based devices.

Post-growth thermal oxidation of wurtzite InN thin films into body-center cubic In2O3 for chemical/gas sensing applications

Post-growth thermal oxidations of InN have been studied using high-resolution x-ray diffraction (HRXRD) and secondary ion-mass spectroscopy (SIMS). The InN thin films, having relative high crystal quality, were grown by metal–organic chemical vapor deposition (MOCVD) on c-sapphire substrates using InGaN/GaN buffer layers. HRXRD reveals that oxidation of wurtzite InN into body-center cubic In2O3 occurred at elevated temperatures. A Si3N4 encapsulation improves the crystal quality of In2O3 oxidized by using conventional rapid thermal annealing (RTA) but it results in the presence of undesired metallic indium. Cycle-RTA not only improves the crystal quality but also avoids the byproduct of metallic indium. SIMS depth profile, using contaminate elements as the ‘interface markers,’ provide evidence that the oxidation of InN is dominated by oxygen inward diffusion mechanism. Together with the HRXRD results, we conclude that the crystal quality of the resultant In2O3/InN heterostructure is mainly controlled by the balance between the speeds of oxygen diffusion and InN thermal dissociation, which can be effectively tuned by cycle-RTA. The obtained In2O3/InN heterostructures can be fundamental materials for studying high speed chemical/gas sensing devices.

Micro-Raman characterization of Ge diffusion and Si stress change in thin epitaxial Si1−xGex layers on Si(100) after rapid thermal annealing

Abstract

Structural and optical study of irradiation effect in GaN epilayers induced by 308 MeV Xe ions

Wurtzite GaN epilayers irradiated at room temperature with 308 MeV 129Xe 35+ ions to fluences of 1 × 10 13 and 3 × 10 13 cm −2 have been studied by contact mode atomic force microscopy (AFM), high-resolution X-ray diffraction (HRXRD), micro-Raman scattering and photoluminescence (PL) spectroscopy. The AFM images showed that the surface of GaN films was etched efficiently due to the Xe ion irradiation. The initial step-terrace structure on GaN surface was eliminated completely at a fluence of 3 × 10 13 cm −2. HRXRD and Raman results indicated that the Xe ion irradiation led to a homogenous lattice expansion throughout the entire ∼3 μm-thick GaN films. The lattice expansion as well as the biaxial compressive stress of the films was increasing with the increase of ion fluence. PL measurements showed that a dominant yellow luminescence band in the as-grown GaN films disappeared, but a blue and a green luminescence bands were produced after irradiation. Based on these results, the strong electronic excitation effect of 308 MeV Xe ions in GaN is discussed.

Quantitative depth profiling of SiGe‐multilayers with the Atom Probe

AbstractThe laser‐assisted Atom Probe has been proposed as a metrology tool for semiconductor technology to meet the requirements accompanying the analysis of the ever smaller and more complex structures targeted for fabrication. In order to support its routine application, we carried out a quantitative assessment of the performance of the Atom Probe (AP) on semiconductor compound multilayers. We analyzed a silicon, silicon‐germanium multilayer structure with Atom Probe Tomography (APT), SIMS, Transmission Electron Microscopy (TEM) and high resolution X‐ray diffraction (HRXRD), and studied the impact of the laser power on the accuracy. Under optimized conditions, the AP outperforms SIMS by a factor of 3 in terms of depth resolution providing a decay length of less than 0.4–0.6 nm/dec whereas the compositions and layer thicknesses are in close agreement with the SIMS, HRXRD and TEM results. Copyright © 2010 John Wiley & Sons, Ltd.

Crystalline perfection, spectroscopic investigations and transport properties of trisglycine zinc chloride NLO single crystal

Bulk single crystals of trisglycine zinc chloride have been grown from aqueous solution by slow cooling technique. Single crystal and powder XRD analyses confirmed orthorhombic crystal structure with non-centrosymmetric space group Pbn2 1. High resolution X-ray diffraction results have established that the quality of the grown crystal is quite good for device fabrication. The crystal was characterized by FTIR and NMR spectral analyses. Optical absorption studies show that the material has very low absorption in the wavelength range 240–2000 nm. The analysis of absorption coefficient in the absorption region reveals a direct band gap of 4.21 eV. The crystal possesses remarkable thermal stability up to 229 °C. Photoconductivity studies of the grown crystal revealed the positive photoconducting nature. The grown crystal exhibited considerable hardness anisotropy with Vicker’s hardness tester. Dielectric constant and dielectric loss were calculated by varying frequencies at different temperatures.