Crystal Rocking Research Articles

Enhanced electrical properties of pulsed Sn-doped (-201) β-Ga2O3 thin films via MOCVD homoepitaxy

Pulsed Sn doping (PSD) homoepitaxial gallium oxide (Ga2O3) films were deposited on (-201) β-Ga2O3 substrates using metal-organic chemical vapor deposition (MOCVD). The study aims to optimize Sn doping conditions to enhance the electrical properties of β-Ga2O3 films. The influence of Sn pulse width (ranging from 0.1 min to 0.3 min) on the morphology, structure, and electrical properties of the film was investigated. The Full Width at Half Maximum (FWHM) of the (-201) crystal plane rocking curve for all doped films is <50 arcsec, indicating high crystal quality. At a Sn pulse width of 0.2 min, we achieve the optimal balance between doping efficiency and crystal quality, resulting in a resistivity of 0.0487 Ω·cm, an electron mobility of 63.5 cm2/V·s, and a carrier concentration of 1.82 × 1018 cm-3. Compared to continuous Sn doping, PSD results in approximately 157 % increase in carrier concentration and 99 % increase in electron mobility. The application of PSD allows sufficient diffusion time for Sn atoms to effectively incorporate into the film, signifying a crucial advancement in enhancing the film's electrical properties and reducing the cost of the metal organic doping source.

Improvement of crystallinity of CdZnTe epilayers on GaSb substrates by ZnTe buffer layer

Thick CdZnTe epitaxial film is a promising alternative for X-ray detectors, especially in the case of large-area imaging application. One of the key issues in growing thick heteroepitaxial film with high crystallinity is to reduce the mismatch dislocations that appear at the interface between CdZnTe epilayer and the substrate. In this paper, we prepared CdZnTe films without and with ZnTe buffer layers on GaSb (001) substrates by the closed space sublimation. All preparation conditions for ZnTe buffer layers, CdZnTe epilayers on ZnTe buffers and GaSb substrates, as well as the pretreatment of GaSb surface have been optimized through tremendous experiments. The results of electron backscatter diffraction and transmission electron microscope observation prove that ZnTe buffer layers suppress (1‾1‾1)M twins extending from GaSb. The deposition temperature for inserting ZnTe buffer about 495 K is optimized for getting smooth ZnTe surface, on which high crystalline quality CdZnTe epilayer with a narrower full-width at half-maximum (85 arcsec) of double crystal X-ray rocking curve for (004) reflection and lower intensity ratio IDcomplex/I(D0, h) of low-temperature photoluminescence spectroscopy were produced.

Preparation of Cd0.8Zn0.2Te/Cd0.5Zn0.5Te/n+-GaAs thick film radiation detectors by close spaced sublimation

High quality Cd0.8Zn0.2Te epitaxial films with a Cd0.5Zn0.5Te buffer layer on n+-GaAs(001) substrates were prepared using a modified close spaced sublimation (CSS) furnace. The effects of the Cd0.5Zn0.5Te buffer layer on crystalline quality and electric properties on Cd0.8Zn0.2Te films were studied using double crystal X-ray rocking curve (DCXRC), atomic force microscope (AFM), scanning electron microscope (SEM), current-voltage (I–V) measurements, and energy spectra tests. The Cd0.5Zn0.5Te buffer layer improved the crystalline quality of a thinner Cd0.8Zn0.2Te film (2 μm) but had less effect on a thick Cd0.8Zn0.2Te film (200 μm). The I–V results showed that the electron injection from n+-GaAs to the Cd0.8Zn0.2Te film can be restrained by the Cd0.5Zn0.5Te buffer layer. Meanwhile, the existing of the Cd0.5Zn0.5Te buffer layer effectively reduced the electronic noise in the spectra tests. Consequently, the modified multi-layer film detector with the Au/Cd0.8Zn0.2Te/Cd0.5Zn0.5Te/n + -GaAs/Au structure showed a considerable resolution of approximately 18% for 241Am@59.5 KeV γ-ray.

Field Electron Emission Characteristics of Single-Crystal GdB6 Conductive Ceramics

Large-size and high-quality single-crystal GdB6 conductive ceramics (length greater than 35 mm and diameter greater than 6 mm) were prepared by optical zone melting, and the single-crystal quality was characterized by single-crystal diffraction, Laue photo, crystal plane rocking curve, and single-crystal fracture scan. Electrochemical corrosion equipment of single-crystal GdB6 conductive ceramic tips was newly designed, which greatly reduced the preparation time of tips from more than 10 h to 2.75 h. The field electron emission current density of the single-crystal GdB6 conductive ceramic tip (r ≈ 500 nm) prepared by the device under applied voltage (2550 V) is 2.24 × 104 A/cm2. This paper also theoretically calculates the electronic structure and electron work function of single-crystal GdB6 under a strong electric field (0.1 V/A). The trapping ability of the B-octahedron in the single crystal GdB6 conductive ceramics against the free electrons of Gd is greatly weakened under a strong electric field (0.1 V/A), and the free electrons also have a certain enrichment phenomenon on the surface of GdB6. The surface barrier of single-crystal GdB6 conductive ceramic will be shortened and narrowed sharply due to the strong electric field (0.1 V/A), which causes the work function of (100) crystal plane of single-crystal GdB6 to decrease sharply (0.38 eV). This causes the free electrons in Gd to have greater energy at the time of emission, and it is easier to get rid of the trap of surface barriers, which is conducive to field electron emission.

Characteristics of multi-crystals monfiguration X-ray diffraction and application in characterizing synchrotron beamline bandwidth

In this paper, the X-ray diffraction experiment with multiple crystals configuration and its application in characterizing the emission characteristics of double crystal monochromator (DCM) on BL09 beamline of Shanghai Synchrotron Radiation Facility (SSRF) are reported. It is a non-dispersion configuration when the second crystal of DCM and the crystal analyzer form a (+&lt;i&gt;n&lt;/i&gt;, –&lt;i&gt;n&lt;/i&gt;) type experimental configuration. The rocking curve of the analyzer crystal can only reflect the operation of the DCM. It is the dispersion configurations when the second crystal of DCM and the crystal analyzer form the (+&lt;i&gt;n&lt;/i&gt;, +&lt;i&gt;n&lt;/i&gt;), (+&lt;i&gt;n&lt;/i&gt;, –&lt;i&gt;m&lt;/i&gt;) and (+&lt;i&gt;n&lt;/i&gt;, +&lt;i&gt;m&lt;/i&gt;) type experimental configuration. The width of the analyzer crystal rocking curve includes not only the intrinsic bandwidth of the DCM and the analyzer crystal, but also the angular divergence of the beamline. In this paper, we use the method of DuMond diagram to explicitly illustrate the characteristics of the output beam of the DCM which can be measured under the above two kinds of experimental configurations, and distinguish the diffraction characteristics of different experimental configurations at the same time. Finally, the angular bandwidth and the relative energy bandwidth of the DCM are 5.40(4) arcsec and1.30(1) × 10&lt;sup&gt;–4&lt;/sup&gt; @ 10 keV, respectively, which are obtained by deconvolution of the analyzer crystal in (+1, –1) nondispersive configuration. The angular distribution and the relative energy bandwidth of the synchrotron radiation beams are 26(1) arcsec and 6.3(2) × 10&lt;sup&gt;–4&lt;/sup&gt; @ 10 keV, respectively, which are obtained by deconvolution of the analyzer crystal and removal of dispersion broadening in (+1, +1), (+1, –3) and (+1, +3) dispersion configuration. After removing the influence of the DCM, the obtained angular divergence of the light source by 25(1) arcsec @ 10 keV, is consistent with the theoretical value of the bending source. In addition, under a series of different white beam entrance slit widths, we characterize the divergence and bandwidth of the beam emitted from the monochromator by the method of multi-crystals dispersion configuration and the DuMond diagram.

Epitaxial characteristics of MBE-grown ZnTe thin films on GaAs (211)B substrates

Highly crystalline ZnTe thin films were grown on GaAs (211)B substrates by molecular beam epitaxy (MBE) for potential applications such as MCT detectors and optoelectronic devices. We investigated the effects of Te to Zn (VI/II) flux ratio on the quality of ZnTe films in terms of crystal orientation, elemental composition, surface roughness, and dislocation density. Atomic concentrations of Zn, Te, and oxygen complexes due to oxygen contamination on the film surfaces were analyzed by X-ray photoelectron spectroscopy. X-ray double crystal rocking curve full width half maximum (FWHM) of ZnTe (422) peak was observed as 233 arcseconds for a 1.66 μm thick film, which indicates high crystallinity. Wet chemical etching was applied to the films to quantify the crystal quality by calculating etch pit densities (EPD) from scanning electron microscope images. A very low EPD value of 1.7 × 107 cm−2 was measured. Additionally, the root mean square roughness values, obtained from atomic force microscopy topography images were in the range of 10–25 nm. These values were supported by FWHM values of red green blue color intensity histograms obtained from Nomarski Microscope images. The results of our analyses indicate that the VI/II flux ratios of 4 and 4.5 produce the best quality ZnTe films on GaAs (211)B substrates.

High x-ray resolving power utilizing asymmetric diffraction from a quartz transmission crystal measured in the 6 keV to 22 keV energy range.

A Cauchois-type spectrometer utilizing the (203) lattice planes at an oblique angle of 11.53° to the normal to the surface of a quartz transmission crystal recorded the Kα and Kβ spectral lines of six elements from Fe to Ag in the 6-22keV energy range from a laboratory x-ray source. After deconvolving the natural lifetime widths and the image plate detector broadening from the observed spectral linewidths, the intrinsic crystal resolving power was determined to be 4000 at the lower energies and decreasing to 1000 at the higher energies. Previously, a Si wafer crystal exhibited twice this resolving power when the (331) planes had been used in asymmetric geometry. The investigation of diffraction with this quartz crystal, with a very similar lattice spacing and therefore spectral coverage, was motivated by the larger integrated reflectivity of quartz due to its well-known quasimosaicity upon elastic bending. The measured spectral linewidths were in good agreement with the widths calculated by accounting for various broadening mechanisms, including source size, crystal thickness, crystal height, crystal rocking curve width, geometrical aberrations, and possible spectrometer configuration errors. This is the first, to the best of our knowledge, demonstration of high resolving power achieved by asymmetric diffraction over a wide energy range (6-22keV) and with detailed comparisons with theoretical broadenings. Based on these results, Cauchois spectrometers employing asymmetric planes of perfect quartz and silicon crystals can be reliably designed and optimized for high-resolution spectroscopy in the >6 keV energy range.

Improvement of crystalline quality of CdZnTe epilayers on GaAs(001) substrates with a two-step growth by Close Spaced Sublimation

A two-step growth process of CdZnTe(001) epilayers on GaAs(001) substrates by Close Spaced Sublimation (CSS) is proposed. The first step, or a so-called pre-growth at low temperature of 350 °C generates more compact nucleation layer than the second step growth at 430 °C, which is more efficient for accelerating grain coalescence and annihilation of defect. Both the double crystal X-ray rocking curve (DCXRC) and the photoluminescence (PL) results prove that CdZnTe film with the best crystalline quality is obtained with the combination of the first step growth at 350 °C and the second growth at 430 °C. Increasing the second step growth temperature from 430 °C to 530 °C and 600 °C deteriorate films crystalline quality due to the increase in thermal stress and Zn content. Current-voltage (IV) measurement and alpha-particle response test indicate that better crystalline quality in CZT film leads to both higher resistivity and better carrier transport property.

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.

Single-Crystal Growth of ZnO:Ga by the Traveling-Solvent Floating-Zone Method

Transparent and blue ZnO:Ga (GZO) single crystals have been grown by the traveling-solvent floating-zone technique using the solvent B2O3 + MoO3 + Nb2O5. The crystals were typically 9–14 mm in diameter and 46–120 mm in length. The largest one was Φ12 mm × 120 mm in size. All GZO crystals were grown along the direction. The growth rate was 0.3–0.5 mm/h, which was far faster than 0.1 mm/day of that grown by the hydrothermal method. The crystalline quality has been characterized by single crystal X-ray diffraction and X-ray rocking curve measurements. Ga substituted on Zn-site and was saturated at about 0.5 wt % of Ga2O3 addition. The GZO crystal doped with 0.5 wt % Ga2O3 has the lowest electrical resistivity of 1.083 × 10–3 Ω·cm and the highest carrier concentration of 1.78 × 1020 cm–3.

Measuring and predicting the diffraction properties of cylindrically bent potassium acid phthalate, KAP(001), crystals.

This report presents the results from measuring the X-ray diffraction properties of a curved potassium acid phthalate (KAP(001)) spectrometer crystal using two measurement methods. One method used a diode type X-ray source and a dual goniometer analysis system, utilizing a flat, perfect KAP(001) crystal as the monochromator. The second method used a synchrotron source and dual crystal Si(111) monochromator. Bent crystals are used in X-ray spectrometers as dispersion elements. These crystals are bent into a circular cylinder section, and this bending can alter the rocking curve properties. The crystal rocking curves were measured for spectral energies ranging from 1250 to 4500 eV. A multi-lamellar model was compared to the measurements and showed good quantitative agreement. This provides a valuable tool for predicting the changes to the KAP (001) for any radius of curvature when the crystal is bent into a cylindrical section.

A technique for measuring the quality of an elliptically bent pentaerythritol [PET(002)] crystal.

We present a technique for determining the X-ray spectral quality from each region of an elliptically curved PET(002) crystal. The investigative technique utilizes the shape of the crystal rocking curve which changes significantly as the radius of curvature changes. This unique quality information enables the spectroscopist to verify where in the spectral range that the spectrometer performance is satisfactory and where there are regions that would show spectral distortion. A collection of rocking curve measurements for elliptically curved PET(002) has been built up in our X-ray laboratory. The multi-lamellar model from the XOP software has been used as a guide and corrections were applied to the model based upon measurements. But, the measurement of RI at small radius of curvature shows an anomalous behavior; the multi-lamellar model fails to show this behavior. The effect of this anomalous RI behavior on an X-ray spectrometer calibration is calculated. It is compared to the multi-lamellar model calculation which is completely inadequate for predicting RI for this range of curvature and spectral energies.

Molecular beam epitaxial growth and optical properties of the CdTe thin films on highly mismatched SrTiO3 substrates

High-quality (111)-orientated CdTe thin films are grown epitaxially on SrTiO3 (001) substrates by molecular beam epitaxy (MBE). The evolution of epitaxial growth was in-situ monitored by reflection high energy electron diffraction. The surface morphologies of the CdTe epitaxial layers (CTELs) are characterized by atomic force microscope, and atomic flat surface is confirmed as the thickness of the CTELs is below ∼40 nm. Three types of X-ray diffraction, including single crystal ω-2θ scan, double crystal X-ray rocking curve and φ-scan, are performed to characterize the structural quality of the CTELs. A full width at half maximum of ∼110 arcsec is yielded when the thickness of the CTELs is beyond ∼100 nm supported by the X-ray rocking curve. And φ-scan illustrates the appearance of four types of domains in the CTELs. Finally, direct band transition is determined, and the temperature dependent transmittance spectra exhibit that the optical band gap decreases from 1.581 eV to 1.503 eV with the temperature from 10 K to 300 K because of the electron-phonon interaction and the lattice thermal expansion.

Development and fabrication of extended short wavelength infrared HgCdTe sensors grown on CdTe/Si substrates by molecular beam epitaxy

The development and fabrication of extended short-wavelength infrared (SWIR) HgCdTe (MCT) sensors grown on CdTe/Si substrates is reported. The MCT epilayers were grown on CdTe/Si substrates by molecular beam epitaxy (MBE). The epilayers were evaluated using Fourier transform infrared spectroscopy (FTIR), X-ray double crystal rocking curve (DCRC), Van der Pauw Hall measurements, dislocation defect–decoration etching and Nomarski microscopy. The FTIR analysis revealed a cutoff wavelength of 2.25μm at 300K which corresponds to a cadmium composition of 47%. As-grown epilayers have void defect densities less than 103cm−2 and etch pit densities of ∼1×107cm−2. The Hall mobilities of annealed MCT samples are on the order of 1500cm2/Vs and have carrier concentrations of ∼1×1016cm−3 at 300K. Samples were doped in situ with indium (donor) and ion-implanted with arsenic (acceptor) to fabricate p–n diodes with sizes ranging from 15μm to 250μm diameter. We present the results and analysis of temperature dependent current–voltage (I–V) and quantum efficiency/responsivity measurements on the p–n diodes. In our analysis, we found that the I–V characteristics of small devices were dominated by shunt currents and quantum efficiency is limited by Shockley–Read–Hall (SRH) mechanisms.

X-ray diffraction on the X-cut of a Ca3TaGa3Si2O14 single crystal modulated by a surface acoustic wave

The result of X-ray diffraction study on a single crystal of the calcium-gallogermanate family Ca3TaGa3Si2O14 (CTGS) modulated by a surface acoustic wave (SAW) is presented. The power flow angle for SAW propagating along the X2 axis of the X-cut in CTGS was measured. The rocking curves for the CTGS crystal were recorded at different amplitudes of an input high frequency electric signal on interdigital transducer used to excite a SAW. Based on the data obtained, intensity dependence of diffraction satellites on the amplitude of electric signal exciting a SAW was built. Numerical simulation of the crystal rocking curves and dependence of diffraction satellite intensities on the SAW amplitude enabled the selection of a set of material constants at which the most complete coincidence of experimental and calculated results is observed.

High-Efficiency and Crack-Free InGaN-Based LEDs on a 6-inch Si (111) Substrate With a Composite Buffer Layer Structure and Quaternary Superlattices Electron-Blocking Layers

In this paper, a composite buffer layer structure (CBLS) with multiple AlGaN layers and grading of Al composition/u-GaN1/(AlN/GaN) superlattices/u-GaN2 and InAlGaN/AlGaN quaternary superlattices electron-blocking layers (QSLs-EBLs) are introduced into the epitaxial growth of InGaN-based light-emitting diodes (LEDs) on 6-inch Si (111) substrates to suppress cracking and improve the crystalline quality and emission efficiency. The effect of CBLS and QSLs-EBL on the crystalline quality and emission efficiency of InGaN-based LEDs on Si substrates was studied in detail. Optical microscopic images revealed the absence of cracks and Ga melt-back etching. The atomic force microscopy images exhibited that the root-mean-square value of the surface morphology was only 0.82 nm. The full widths at half maxima of the (0002) and (1012) reflections in the double crystal X-ray rocking curve were ~330 and 450 respectively. The total threading dislocation density, revealed by transmission electron microscopy, was <; 6× 108 cm-2. From the material characterizations, described above, blue and white LEDs emitters were fabricated using the epiwafers of InGaN-based LEDs on 6-inch Si substrates. The blue LEDs emitter that comprised blue LEDs chip and clear lenses had an emission power of 490 mW at 350 mA, a wall-plug efficiency of 45% at 350 mA, and an efficiency droop of 80%. The white LEDs emitter that comprised blue LEDs chip and yellow phosphor had an emission efficiency of ~110 lm/W at 350 mA and an efficiency droop of 78%. These results imply that the use of a CBLS and QSLs-EBL was found to be very simple and effective in fabricating high-efficiency InGaN-based LEDs on Si for solid-state lighting applications.

Solid-state grain growth of garnet single crystals of complex composition

Various (Nd-doped (Y,Gd,La,Lu)3(Sc,Al)5O12) garnets were reproducibly grown from a Nd-doped (Y,Gd,La,Lu)3(Sc,Al)5O12 polycrystalline precursor. Single crystals were grown through controlled abnormal grain growth at temperatures between 1750°C and 1850°C. Nd-doped (Y,Gd,La,Lu)3(Sc,Al)5O12 powder was prepared using the co-precipitation method, and single crystals were fabricated by the conversion of polycrystalline material. The phase identification of the specimens was performed using XRD and X-ray double crystal rocking curve (DCRC) analysis. The absorption spectra, fluorescence spectra, and fluorescence lifetimes of samples excited using an 808nm laser diode (LD) were also measured. The fluorescence lifetime of Nd-doped (Y,Gd,La,Lu)3(Sc,Al)5O12 single crystals is longer than that of Nd:YAG; a prolonged fluorescence lifetime helps to achieve a high laser output power. In short, we can fabricate complex mixed-garnet single crystals using the solid-state single-crystal conversion (SCC) method.

Growth and Electrical Properties of ZnAl2Se4 Single Crystal Thin Film by Hot Wall Epitaxy

A stoichiometric mixture of evaporating materials for <TEX>$ZnAl_2Se_4$</TEX> single-crystal thin films was prepared in a horizontal electric furnace. These <TEX>$ZnAl_2Se_4$</TEX> polycrystals had a defect chalcopyrite structure, and its lattice constants were <TEX>$a_0=5.5563{\AA}$</TEX> and <TEX>$c_0=10.8897{\AA}$</TEX>.To obtain a single-crystal thin film, mixed <TEX>$ZnAl_2Se_4$</TEX> crystal was deposited on the thoroughly etched semi-insulating GaAs(100) substrate by a hot wall epitaxy (HWE) system. The source and the substrate temperatures were <TEX>$620^{\circ}C$</TEX> and <TEX>$400^{\circ}C$</TEX>, respectively. The crystalline structure of the single-crystal thin film was investigated by using a double crystal X-ray rocking curve and X-ray diffraction <TEX>${\omega}-2{\theta}$</TEX> scans. The carrier density and mobility of the <TEX>$ZnAl_2Se_4$</TEX> single-crystal thin film were <TEX>$8.23{\times}10^{16}cm^{-3}$</TEX> and <TEX>$287m^2/vs$</TEX> at 293 K, respectively. To identify the band gap energy, the optical absorption spectra of the <TEX>$ZnAl_2Se_4$</TEX> single-crystal thin film was investigated in the temperature region of 10-293 K. The temperature dependence of the direct optical energy gap is well presented by Varshni's relation: <TEX>$E_g(T)=E_g(0)-({\alpha}T^2/T+{\beta})$</TEX>. The constants of Varshni's equation had the values of <TEX>$E_g(0)=3.5269eV$</TEX>, <TEX>${\alpha}=2.03{\times}10^{-3}eV/K$</TEX> and <TEX>${\beta}=501.9K$</TEX> for the <TEX>$ZnAl_2Se_4$</TEX> single-crystal thin film. The crystal field and the spin-orbit splitting energies for the valence band of the <TEX>$ZnAl_2Se_4$</TEX> were estimated to be 109.5 meV and 124.6 meV, respectively, by means of the photocurrent spectra and the Hopfield quasicubic model. These results indicate that splitting of the <TEX>${\Delta}so$</TEX> definitely exists in the <TEX>${\Gamma}_5$</TEX> states of the valence band of the <TEX>$ZnAl_2Se_4/GaAs$</TEX> epilayer. The three photocurrent peaks observed at 10 K are ascribed to the <TEX>$A_1$</TEX>-, <TEX>$B_1$</TEX>-exciton for n = 1 and <TEX>$C_{21}$</TEX>-exciton peaks for n = 21.

X-ray phase contrast imaging of objects with subpixel-size inhomogeneities: a geometrical optics model

Several x-ray phase contrast extraction algorithms use a set of images acquired along the rocking curve of a perfect flat analyzer crystal to study the internal structure of objects. By measuring the angular shift of the rocking curve peak, one can determine the local deflections of the x-ray beam propagated through a sample. Additionally, some objects determine a broadening of the crystal rocking curve, which can be explained in terms of multiple refraction of x rays by many subpixel-size inhomogeneities contained in the sample. This fact may allow us to differentiate between materials and features characterized by different refraction properties. In the present work we derive an expression for the beam broadening in the form of a linear integral of the quantity related to statistical properties of the dielectric susceptibility distribution function of the object.

In situ grown Ge in an arsenic-free environment for GaAs/Ge/GaAs heterostructures on off-oriented (100) GaAs substrates using molecular beam epitaxy

High-quality epitaxial Ge layers for GaAs/Ge/GaAs heterostructures were grown in situ in an arsenic-free environment on (100) off-oriented GaAs substrates using two separate molecular beam epitaxy (MBE) chambers, connected via vacuum transfer chamber. The structural, morphological, and band offset properties of these heterostructures are investigated. Reflection high energy electron diffraction studies exhibited (2 × 2) Ge surface reconstruction after the growth at 450 °C and also revealed a smooth surface for the growth of GaAs on Ge. High-resolution triple crystal x-ray rocking curve demonstrated high-quality Ge epilayer as well as GaAs/Ge/(001)GaAs heterostructures by observing Pendellösung oscillations and that the Ge epilayer is pseudomorphic. Atomic force microscopy reveals smooth and uniform morphology with surface roughness of ∼0.45 nm and room temperature photoluminescence spectroscopy exhibited direct bandgap emission at 1583 nm. Dynamic secondary ion mass spectrometry depth profiles of Ga, As, and Ge display a low value of Ga, As, and Ge intermixing at the Ge/GaAs interface and a transition between Ge/GaAs of less than 15 nm. The valence band offset at the upper GaAs/Ge-(2 × 2) and bottom Ge/(001)GaAs-(2 × 4) heterointerface of GaAs/Ge/GaAs double heterostructure is about 0.20 eV and 0.40 eV, respectively. Thus, the high-quality heterointerface and band offset for carrier confinement in MBE grown GaAs/Ge/GaAs heterostructures offer a promising candidate for Ge-based p-channel high-hole mobility quantum well field effect transistors.