Double Crystal X-ray Diffraction Research Articles

Improved Output Power of 380 nm InGaN-Based LEDs Using a Heavily Mg-Doped GaN Insertion Layer Technique

High-performance InGaN-based 380 nm UV LEDs are fabricated by using a heavily Mg-doped GaN insertion layer (HD-IL) technique. Based on the transmission electron microscopy, etch pit density, and cathodoluminescence results, the HD-IL technique can substantially reduce the defect density of GaN layer. The double-crystal X-ray diffraction results are in good agreement with those observations. The internal quantum efficiency of LED sample with an HD-IL shows around 40% improvement compared with the LED sample without the use of HD-IL. When the vertical-type LED chips (size: 1 mm times 1 mm) are driven by a 350 mA current, the output powers of the LEDs with and without an HD-IL are measured to be 203.4 and 158.9 mW, respectively. As much as 28% increased light output power is achieved.

Effect of annealing on electrical properties of InAsSb films grown on GaAs substrates by molecular beam epitaxy

InAs 0.3Sb 0.7 layers with mirror-like morphology have been grown on GaAs substrates directly by molecular beam epitaxy. A room-temperature electron Hall mobility of 3×10 4 cm 2/V s has been obtained for a 2.4-μm-thick layer by annealing at 200 °C. For the sample annealed at 200 °C, the electron Hall mobility does not change much with the variation of temperature. When the specimens are annealed at 300 °C, the Hall mobility is lower than that of the specimen without annealing. It can be interpreted by the segregation of Sb and the evaporation of As according to the results of X-ray photoelectron spectrum and the degeneracy of the quality of the film according to double crystal X-ray diffraction.

Improvement of crystal quality of GaN grown on AlN template by MOCVD using HT‐AlN interlayer

AbstractTwo GaN samples, with and without high temperature (HT)‐AlN interlayer (labelled as sample A and B, respectively) grown by MOCVD on AlN template, were investigated by double‐crystal X‐ray diffraction (DC‐XRD), photoluminescence (PL), and atomic force microscope (AFM) measurements. It was found that the crystal quality of GaN could be greatly improved by the HT‐AlN interlayer. The full width at half maximum (FWHM) of (102) reflection in XRD rocking curve was narrower for sample A than that for sample B. However, the FWHMs of (002) reflections were almost the same for the two samples. In addition, the tilt degree which reflected screw dislocation density was almost the same, while the twist degree which reflected edge dislocation density changed from 0.214° to 0.152° when the HT‐AlN interlayer was used. Both the intensities of (102) reflection in XRD and band edge emission in PL for sample A were stronger too. In the AFM images, the atomic growth steps of sample A were clearer than those of sample B. According to the results of the in situ optical reflectivity spectra and the atomic force microscope (AFM) images, the above results were attributed to the three‐dimensional (3D) growth mode of the HT‐AlN interlayer. The HT‐AlN interlayer may work as a kind of “micro‐area” seed for epitaxial lateral overgrowth (ELOG) resulting in bending some dislocations. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Ultra-Shallow Junction Formation by Plasma doping and Excimer Laser Annealing

Plasma doping (PLAD) process using PH3 plasma is presented to fabricate n+/p ultra shallow junction at room temperature. Directly after the PLAD, a pre-annealing has been conducted for 5 min at 500 {degree sign}C in thermal furnace. ArF excimer laser annealing (ELA) process was then followed with an increment of 20 mJ/cm2 in the laser energy ranging from 400 to 500 mJ/cm2. When the laser energy density was larger than 460 mJ/cm2, a reduced sheet resistance was observed. In order to examine the crystalline defects generated during PLAD, the transmission electron microscopy (TEM) and double crystal X-ray diffraction (DXRD) measurements have been made. With optimized PLAD and ELA conditions, junction depth of 30 nm and sheet resistance of 151.6 Ω/□ could be obtained.

Growth and characterization of GaAs layers on polished Ge/Si by selective aspect ratio trapping

Epitaxial GaAs layers have been deposited on polished Ge film grown on exactly (0 0 1) oriented Si substrate by metal-organic chemical vapor deposition (MOCVD) via aspect ratio trapping (ART) method. Double-crystal X-ray diffraction shows that the full-width at half-maximum (FWHM) of the (4 0 0) reflection obtained from 1 μm GaAs is 140 arcsec. Scanning electron microscopy (SEM) of the GaAs layer surface shows that the amount of antiphase domain defects (APD) raised from GaAs/Ge interface using Ge ART on Si is dramatically reduced compared to GaAs layers grown on exact (0 0 1) Ge substrate. Defect reduction and Ge diffusion at vicinal GaAs/Ge interface were investigated via cross-section transmission electron microscopy (X-TEM) and secondary ion mass spectrometry (SIMS). Film morphology and optical properties were evaluated via SEM and room temperature photoluminescence (PL).

Defect reduction of laterally regrown GaN on GaN/patterned sapphire substrates

Structural properties of GaN epilayers on wet-etched protruding and recess-patterned sapphire substrates (PSSs) have been investigated in detail using high-resolution double-crystal X-ray diffraction (DCXRD) and etch-pit density methods. The DCXRD results reveal various dislocation configurations on both types of PSSs. The etch pits of GaN on the recess PSS exhibit a regular distribution, i.e. less etch pits or threading dislocation density (TDD) onto the recess area than those onto the sapphire mesas. On the contrary, an irregular distribution is observed for the etch pits of GaN on the protruding PSS. A higher crystal quality of the GaN epilayer grown onto the recess PSS can be achieved as compared with that onto the protruding PSS. These data reflect that the GaN epilayer on the recess PSS could be a better template for the second epitaxial lateral overgrowth (ELOG) of GaN. As a result, the GaN epilayers after the ELOG process display the TDDs of around ∼10 6 cm −2.

Improved optical performance of GaN grown on pattered sapphire substrate

An improved GaN film with low dislocation density was grown on a C-face patterned sapphire substrate (PSS) by metalorganic chemical vapor deposition (MOCVD). The vapor phase epitaxy starts from the regions with no etched pits and then spreads laterally to form a continuous GaN film. The properties of the GaN film have been investigated by double crystal X-ray diffraction (DCXRD), atomic force microscopy (AFM) and photoluminescence (PL), respectively. The full-width at half-maximum (FWHM) of the X-ray diffraction curves (XRCs) for the GaN film grown on PSS in the (0002) plane and the (101̄2) plane are as low as 312.80 arcsec and 298.08 acrsec, respectively. The root mean square (RMS) of the GaN film grown on PSS is 0.233 nm and the intensity of the PL peak is comparatively strong.

Growth of Sb-Bi gradient single crystals

The growth conditions and structural quality of Sb-Bi gradient single crystals with Bi content from 2 to 18 at %, grown by the Czochralski method with solid phase feed, are investigated. Bi distribution in the crystals along their pulling direction are studied by electron probe microanalysis and the change in the interplanar spacing is analyzed by double-crystal X-ray diffraction. It is established that the pulling rate and feed mass affect the Bi distribution in Sb-Bi single crystals.

Laser lift-off technique and the re-utilization of GaN-based LED films grown on sapphire substrate

A thin GaN LED film, grown on 2-inch-diameter sapphire substrates, is separated by laser lift-off. Atom force microscopy (AFM) and the double-crystal X-ray diffraction (XRD) have been employed to characterize the performance of GaN before and after the lift-off process. It is demonstrated that the separation and transfer processes do not alter the crystal quality of the GaN films obviously. InGaN/ GaN multi-quantum-wells (MQW’s) structure is grown on the separated sapphire substrate later and is compared with that grown on the conventional substrate under the same condition by using PL and XRD spectrum.

Investigation of the effect of growth interruption on the formation of InAs/GaAs quantum dot superlattice near the InAs critical thickness

Two kinds of superlattices (i) with and (ii) without growth interrupt (GI) after deposition of 1.77 monolayers (ML) of InAs on GaAs (0 0 1) were grown by solid-source molecular beam epitaxy (MBE) and assessed by transmission electron microscopy (TEM) techniques, double crystal X-ray diffraction (DCXRD) and photoluminescence (PL) measurements in order to gain an understanding of the structural and compositional properties. In case (i) formation of coherent dislocation free self-organized quantum dots (SOQDs) with 2.8–3.2 nm height and 13–16 nm lateral size was observed, whereas in case (ii) no quantum dots had formed. In order to better understand the implication of growth interruption for the formation mechanism, highly localised assessment of the composition of the QD was carried out via atomic resolution Z-contrast imaging and electron energy loss spectroscopy (EELS).

Interaction of low-temperature surfactant-grown InAs superlattice layers with arsenic precipitates

Double crystal X-ray diffraction (DCXRD), transmission electron microscopy (TEM) and photoluminescence (PL) measurements were used to study the effect of post-growth annealing temperature on the structural properties of novel low growth (250 °C) and normal growth (450 °C) temperature InAs surfactant-mediated grown materials. Under conditions of “arsenic-free” growth, high-quality InAs–GaAs superlattices are obtained at low temperatures (LT) even at thicknesses as high as 3 monolayers (MLs) for InAs. The interaction of the built-in strain fields and the point defects in LT-GaAs both before and after annealing has been studied in detail. DCXRD studies show that the thickness of the LT-grown InAs layers decreased by up to 0.7 ML as the annealing temperature increased to 550 °C. There is evidence from the DCXRD and TEM that the LT InAs–GaAs superlattice structure starts to distort at annealing temperatures above 450 °C. In comparison, the sample grown at normal temperature, 450 °C, still retained the periodicity of the superlattice layers up to an annealing temperature of 650 °C without any change in the thickness of either the InAs (wetting layer) or GaAs.

Influence of growth rate in the early stage of high temperature GaN layer growth on quality of GaN films

The effect of growth rate in the early stage of high temperature (HT) GaN layer growth on the quality of GaN by MOCVD has been investigated. The properties of GaN layers were measured by double crystal X-ray diffraction (DCXRD), Hall method, photoluminescence, and atomic force microscopy, respectively. The results reveal that the quality of GaN layers is influenced by the growth rate of HT GaN growth in the early stage. The properties of GaN layers are obviously improved by decreasing the growth rate in the early stage of HT GaN growth properly. However, when the growth rate decreases to some extent, the quality of GaN layer deteriorates instead. The reasons behind this phenomenon were discussed.

Improved Light Output of Nitride-Based Light-Emitting Diodes by Lattice-Matched AlInN Cladding Structure

We report the growth of AlInN nearly lattice-matched to GaN using metal-organic vapor phase epitaxy. The full-width at half-maximum of the AlInN peak measured by double crystal X-ray diffraction was 219.8 arcsec for the indium content of 20.8%. The effects of AlInN cladding layers on InGaN-GaN multiple-quantum-well light-emitting diodes (LEDs) were also investigated. From the room-temperature photoluminescence spectra, the shorter emission wavelength and the higher intensity were observed after employing AlInN cladding layers. Compared to the conventional LED, the light output intensity of the LED with AlInN cladding layers was increased due to the enhanced carrier confinement. Besides, we found the light output intensity could be saturated at higher injection current. Although the electrical property of the LED with AlInN cladding layers was slightly degraded, the experimental results in this study could explain the potential applicability of AlInN to the fabrication of cladding layers.

Study of the relationship between the crystal structure of nanolayers and electrical properties in Al x Ga1−x As/In y Ga1−y As pseudobinary heterostructures by double-crystal X-ray diffraction

The structural parameters of individual layers of samples of a Al{sub x}Ga{sub 1-x}As/In{sub y}Ga{sub 1-y}As/GaAs pseudomorphic heterostructure have been determined by double-crystal X-ray diffraction. A relationship of the technological parameters of fabrication of heterostructures with their structural and electrical properties is established. The increase in the mobility of the 2D electron gas in the samples under study, caused by the increase in the growth temperature of the Al{sub x}Ga{sub 1-x}As spacer layer and the decrease in the time of silicon {delta} doping from the two sides of the quantum well, correlates well with the degree of the sample structural quality.

Hot Wall Epitaxy (HWE)법에 의한 ZnIn2S4단결정 박막 성장과 가전자대 갈라짐에 대한 광전류 연구

Single crystal <TEX>$ZnIn_{2}S_{4}$</TEX> layers were grown on a thoroughly etched semi-insulating GaAs(100) substrate at <TEX>$450^{\circ}C$</TEX> with the hot wall epitaxy (HWE) system by evaporating the polycrystal source of <TEX>$ZnIn_{2}S_{4}$</TEX> at <TEX>$610^{\circ}C$</TEX> prepared from horizontal electric furnace. The crystalline structure of the single crystal thin films was investigated by the photoluminescence and double crystal X-ray diffraction (DCXD). The carrier density and mobility of single crystal <TEX>$ZnIn_{2}S_{4}$</TEX> thin films measured with Hall effect by van der Pauw method are <TEX>$8.51{\times}10^{17}\;electron/cm^{-3}$</TEX>, <TEX>$291{\;}cm^{2}/v-s$</TEX> at 293 K, respectively. The photocurrent and the absorption spectra of <TEX>$ZnIn_{2}S_{4}$</TEX>/SI(Semi-Insulated) GaAs(100) are measured ranging from 293 K to 10 K. The temperature dependence of the energy band gap of the <TEX>$ZnIn_{2}S_{4}$</TEX> obtained from the absorption spectra was well described by the Varshni's relation, <TEX>$E_g(T)$</TEX>=2.9514 eV. (<TEX>$7.24{\times}10^{-4}\;eV/K$</TEX>)<TEX>$T^{2}$</TEX>/(T+489 K). Using the photocurrent spectra and the Hopfield quasicubic model, the crystal field energy(<TEX>${\Delta}cr$</TEX>) and the spin-orbit splitting energy(<TEX>${\Delta}so$</TEX>) for the valence band of the <TEX>$ZnIn_{2}S_{4}$</TEX> have been estimated to be 167.8 meV and 14.8 meV at 10 K, respectively. The three photocurrent peaks observed at 10 K are ascribed to the <TEX>$A_{1}$</TEX>-, <TEX>$B_{1}$</TEX>-, and <TEX>$C_{41}$</TEX>-exciton peaks.

Characteristics Comparison between GaN Epilayers Grown on Patterned and Unpatterned Sapphire Substrate (0001)

GaN epilayers were grown on lens shaped patterned sapphire substrate (PSS) (0001) and unpatterned sapphire substrate (UPSS) (0001) by metal-organic chemical vapor deposition (MOCVD). The quality of the grown GaN epilayers on the PSS and UPSS were compared. Structural characteristics, surface morphology and optical properties of the GaN epilayers were investigated using double crystal X-ray diffraction (DCXRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and photoluminescence (PL). A lens shaped pattern was formed on the sapphire substrate to reduce threading dislocation (TD) density and also to improve the optical emission efficiency by internal reflection on the lens. Scanning electron microscopy images show the growth of GaN epilayers at various times. Full coalescence is observed at a growth time of 80 min. It is seen from the DCXRD rocking spectrum that full width at half maximum (FWHM) of the GaN grown on PSS was 438.7 arcsec which is less than UPSS value. The lower value of FWHM indicates that the crystalline quality of the GaN epilayers grown on PSS is improved compared to GaN grown on UPSS. It is clearly seen from the AFM images that the dislocation density is less for the GaN grown on PSS. A strong and sharp photoluminescence (PL) band edge emission was observed for the GaN grown on PSS compared to UPSS. Defect related yellow luminescence was observed for GaN grown on UPSS which did not appear for PSS. The FWHM at the 364.3 nm peak position was evaluated to be 50.7 meV from the PL spectra for GaN grown on PSS. The above result indicates GaN epilayers can be grown on PSS with low TD density and will be useful for optical emission.

Hot Wall Epitaxy(HWE)법에 의한 CdGa2Se4단결정 박막 성장과 열처리 효과

The stochiometric mix of evaporating materials for the <TEX>$CdGa_2Se_4$</TEX> single crystal thin films was prepared from horizontal furnace. To obtain the single crystal thin films, <TEX>$CdGa_2Se_4$</TEX> mixed crystal was deposited on thoroughly etched semi-insulating GaAs(100) substrate by the Hot Wall Epitaxy (HWE) system. The source and substrate temperature were <TEX>$630^{\circ}C$</TEX> and <TEX>$420^{\circ}C$</TEX>, respectively. The crystalline structure of single crystal thin films was investigated by the photoluminescence and double crystal X-ray diffraction (DCXD).The carrier density and mobility of <TEX>$CdGa_2Se_4$</TEX> single crystal thin films measured from Hall effect by van der Pauw method are <TEX>$8.27{\times}10^{17}\;cm^{-3},\;345\;cm^2/V{\cdot}s$</TEX> at 293 K. respectively. The temperature dependence of the energy band gap of the <TEX>$CdGa_2Se_4$</TEX> obtained from the absorption spectra was well described by the Varshni's relation, <TEX>$Eg(T)\;=\;2.6400\;eV\;-\;(7.721{\times}10^{-4}\;eV/K)T^2/(T+399\;K)$</TEX>. After the as-grown single crystal <TEX>$CdGa_2Se_4$</TEX> thin films were annealed in Cd-, Se-, and Ga -atmospheres, the origin of point defects of single crystal <TEX>$CdGa_2Se_4$</TEX> thin films has been investigated by PL at 10 K. The native defects of <TEX>$V_{Cd}$</TEX>, <TEX>$V_{Se}$</TEX>, <TEX>$Cd_{int}$</TEX>, and <TEX>$Se_{int}$</TEX> obtained by PL measurements were classified as donors or accepters. We concluded that the heat-treatment in the Cd-atmosphere converted single crystal <TEX>$CdGa_2Se_4$</TEX> thin films to an optical p-type. Also, we confirmed that Ga in <TEX>$CdGa_2Se_4/GaAs$</TEX> did not form the native defects because Ga in single crystal <TEX>$CdGa_2Se_4$</TEX> thin films existed in the form of stable bonds.

Effects of growth temperature of AlGaN buffer layer on the properties of Al0.58Ga0.42N epilayer by NH3‐MBE

AbstractAl0.58Ga0.42N epilayers are grown by ammonia gas source molecular beam epitaxy (NH3‐MBE) on (0001) sapphire substrate using AlGaN buffer layer. The effects of the buffer layer growth temperature on the properties of Al0.58Ga0.42N epilayer are especially investigated. In‐situ high‐energy electron diffraction (RHEED), double‐crystal X‐ray diffraction (DCXRD), atomic force microscopy (AFM), photoconductivity measurement and cathodoluminescence (CL) are used to characterize the samples. It is found that high growth temperature of AlGaN buffer layer would improve the crystalline quality, surface smoothness, optical quality and uniformity of the Al0.58Ga0.42N epilayer. The likely reason for such improvements is also suggested. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Investigation on Large-Sized Sapphire Crystalline Perfection by X-Ray Double-Crystal Diffraction Method

The large-sized sapphire (Ø225×205 mm, 27.5 kg) was grown successfully by SAPMAC method (sapphire growth technique with micro-pulling and shoulder-expanding at cooled center). The surface quality of the specimens was characterized by micro-Raman spectroscopy, and double crystal X-ray diffractometry (DCD) was utilized to investigate its crystalline perfection. The measurement of rocking curves was performed on various specimens from different region of large sapphire boule. The experimental results showed that CMP (chemo-mechanical polishing) with subsequent suitable chemically etching can develop the best-quality sapphire crystal surface and the values of FWHM obtained by conventional DCD were in the range from 27” to 58”. The infrared spectral transmission (2.0-4.5 5m) of sapphire crystal exceeded 82%. It is confirmed of SAPMAC growth method characteristics with in-situ annealing, small temperature gradient and low residual stress level by numerical simulation analysis.

Characteristics comparison between GaN epilayers grown on patterned and unpatterned sapphire substrate (0 0 0 1)

GaN epilayers were grown on lens-shaped-pattern sapphire substrate (PSS) (0 0 0 1) and unpatterned sapphire substrate (UPSS) (0 0 0 1) by metal-organic chemical vapor deposition (MOCVD). The quality of the grown GaN epilayers on the PSS and UPSS were compared. Structural characteristics, surface morphology and optical properties of the GaN epilayers were investigated using double crystal X-ray diffraction (DCXRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and photoluminescence (PL). A lens-shaped pattern was formed on the sapphire substrate to reduce threading dislocation (TD) density and also to improve the optical emission efficiency by internal reflection on the lens. SEM images show the growth of GaN epilayers at various times. Full coalescence is observed at a growth time of 80 min. It is seen from the DCXRD rocking spectrum that full width at half maximum (FWHM) of the GaN grown on PSS was 438.7 arcsec which is less than UPSS value. The lower value of FWHM indicates that the crystalline quality of the GaN epilayers grown on PSS is improved compared to GaN grown on UPSS. It is clearly seen from the AFM images that the dislocation density is less for the GaN grown on PSS. A strong and sharp PL band edge emission was observed for the GaN grown on PSS compared to UPSS. Defect related yellow luminescence was observed for GaN grown on UPSS which did not appear for PSS. The FWHM at the 364.3 nm peak position was evaluated to be 50.7 meV from the PL spectra for GaN grown on PSS. The above result indicates GaN epilayers can be grown on PSS with low TD density and will be useful for optical emission.