Double Crystal X-ray Diffraction Research Articles

Zinc-induced lattice contraction in metalorganic vapor phase epitaxy grown AlGaInP

p-Type Zn doped (AlxGa1-x)0.5In0.5P layers have been grown on (001) GaAs substrates by metalorganic vapor phase epitaxy. The lattice constants have been carefully measured by X-ray double crystal diffraction. Mismatches between the substrates and epitaxial layers are observed in the direction corresponding to lattice contraction. The variation of fully-relaxed lattice constants calculated from symmetric (004) and asymmetric (115) diffraction shows that the contraction is related to both increasing inlet dopant flows and increasing growth temperatures. Secondary ion mass spectrometry is employed to analyze the elements in the epitaxial layers. The variations of Al, Ga, In and Zn components indicate that a decrease of In incorporation during the growth leads to the contracted lattice, although Zn atoms, which incorporate into the sites of In atoms during the doping, are smaller in covalent radius. The decrease is supposed to be caused by the competition between In and Zn atoms on the growth surface, which is well fit by the surface adsorption-trapping model. In addition, the suppression of Al and Ga incorporation by inlet dopant flows is observed. The possible cause might be the ethane generated by the pyrolysis of dopant source, which impedes the decomposition process of metalorganic sources of Al and Ga atoms.

Growth and optimization of InxGayAl1−x−ySb buffer layers for electronic and optoelectronic applications

InxGayAl1−x−ySb alloys have been grown by molecular beam epitaxy for use as a buffer layer for growing semiconductors on GaAs substrates with lattice constants beyond that of AlSb. This is an extension of the use of AlxGa1−xSb alloys to accommodate for the lattice mismatch with semi-insulating GaAs substrates. The growth of In0.21Ga0.19Al0.6Sb with a 6.2 Å lattice constant on semi-insulating GaAs substrates is the focus of this work. Several measures of the quality of a 1 μm-thick In0.21Ga0.19Al0.6Sb layer improved when the growth temperature was increased from 460 to 600 °C. Atomic force microscopy root-mean-square values decreased from 2.9 to 1.8 nm and the peak-to-valley values decreased from 17.7 to 9.7 nm. In addition, double crystal x-ray diffraction ω-2Θ spectra linewidths decreased from 568 to 482 arc sec. At the lower growth temperatures, several photoluminescence (PL) peaks associated with radiative recombination from regions with different alloy compositions were found. However, on increasing the growth temperature a single PL line was observed, strongly suggesting a more uniform alloy composition.

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

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

MBE Growth of Mid-wave Infrared HgCdTe Layers on GaSb Alternative Substrates

GaSb has been studied as a new alternative substrate for growing HgCdTe via molecular beam epitaxy (MBE). Cross-sectional transmission electron microscopy (TEM) studies indicate that MBE-grown CdTe buffer layers on GaSb have much lower misfit dislocation density than comparable layers grown on GaAs. The MBE-grown mid-wave infrared (MWIR) HgCdTe layers on GaSb substrates present material quality comparable to those grown on GaAs substrates, which is one of the state-of-the-art alternative substrates currently used to grow HgCdTe for the fabrication of MWIR detectors and focal plane arrays. Typically, HgCdTe materials grown on GaSb are found to have a rocking curve (double crystal x-ray diffraction) full width at half maximum of ~122 arcsec and an etch pit density of ~mid-106 cm–2. Electron backscatter diffraction mapping shows that the lattice misorientation/misfit dislocations near the HgCdTe/CdTe interface are negligible for GaSb substrates in comparison to GaAs substrates, and that the material quality of the HgCdTe layer on GaSb is determined primarily by the material quality of the CdTe buffer layer. These preliminary results are very encouraging considering that this is a relatively recent research effort, and higher quality MBE-grown HgCdTe materials are expected on GaSb substrates with further optimization of HgCdTe growth conditions as well as further improvements in the growth conditions for CdTe buffer layers.

Hot Wall Epitaxy(HWE)법에 의한 MnAl2S4단결정 박막 성장과 광전도 특성

수평 전기로에서 <TEX>$MnAl_2S_4$</TEX> 다결정을 합성하여 HWE(Hot Wall Epitaxy)방법으로 <TEX>$MnAl_2S_4$</TEX> 단결정 박막을 반절연성 GaAs(100)기판에 성장시켰다. <TEX>$MnAl_2S_4$</TEX> 단결정 박막의 성장 조건은 증발원의 온도 <TEX>$630^{\circ}C$</TEX>, 기판의 온도 <TEX>$410^{\circ}C$</TEX>였고 성장 속도는 <TEX>$0.5{\mu}m/hr$</TEX>였다. 이때 <TEX>$MnAl_2S_4$</TEX> 단결정 박막의 결정성의 조사에서 이중결정 X-선 요동곡선(DCRC)의 반폭치(FWHM)도 132 arcsec로 가장 작아 최적 성장 조건임을 알 수 있었다. <TEX>$MnAl_2S_4$</TEX>/SI(Semi-Insulated) GaAs(100) 단결정 박막의 광흡수를 293 K에서 10 K까지 측정하였다. 광흡수 스펙트럼으로부터 band gap <TEX>$E_g(T)$</TEX>는 Varshni 공식에 따라 계산한 결과 <TEX>$E_g(T)=3.7920eV-(5.2729{\times}10^{-4}eV/K)T^2/(T+786K)$</TEX>였다. <TEX>$MnAl_2S_4$</TEX> 단결정 박막의 응용소자인 photocell로 사용할 수 있는 pc/dc 값이 가장 큰 광전도셀은 S 증기분위기에서 열처리한 셀로 <TEX>$1.10{\times}10^7$</TEX>이었으며, 광전도 셀의 감도(sensitivity)도 S 증기분위기에서 열처리한 셀이 0.93로 가장 좋았다. 또한 최대 허용소비전력(MAPD)값도 S 증기분위기에서 열처리한 셀이 316 mW로 가장 좋았으며, S 증기분위기에서 열처리한 셀의 응답시간은 오름시간 14.8 ms, 내림시간 12.1 ms로 가장 빠르게 나타나, <TEX>$MnAl_2S_4$</TEX> 단결정 박막을 S 분위기에서 <TEX>$290^{\circ}C$</TEX>로 30분 열처리한 photocell이 상용화가 가능할 것으로 여겨진다. A stoichiometric mixture of evaporating materials for <TEX>$MnAl_2S_4$</TEX> single crystal thin films was prepared from horizontal electric furnace. To obtain the single crystal thin films, <TEX>$MnAl_2S_4$</TEX> mixed crystal was deposited on thoroughly etched semi-insulating GaAs(100) substrate by the Hot Wall Epitaxy (HWE) system. The source and substrate temperatures were <TEX>$630^{\circ}C$</TEX> and <TEX>$410^{\circ}C$</TEX>, respectively. The crystalline structure of the single crystal thin films was investigated by the photoluminescence and double crystal X-ray diffraction (DCXD). The temperature dependence of the energy band gap of the <TEX>$MnAl_2S_4$</TEX> obtained from the absorption spectra was well described by the Varshni's relation, <TEX>$E_g(T)=3.7920eV-5.2729{\times}10^{-4}eV/K)T^2/(T+786 K)$</TEX>. In order to explore the applicability as a photoconductive cell, we measured the sensitivity (<TEX>${\gamma}$</TEX>), the ratio of photocurrent to dark current (pc/dc), maximum allowable power dissipation (MAPD) and response time. The results indicated that the photoconductive characteristic were the best for the samples annealed in S vapour compare with in Mn, Al, air and vacuum vapour. Then we obtained the sensitivity of 0.93, the value of pc/dc of <TEX>$1.10{\times}10^7$</TEX>, the MAPD of 316 mW, and the rise and decay time of 14.8 ms and 12.1 ms, respectively.

AlN 단결정의 품질평가를 위한 molten KOH/NaOH eutectic alloy의 화학적 습식에칭

본 연구에서는 상용화되는 AlN 웨이퍼(wafer)를 이용하여 molten KOH/NaOH 화학적 습식 에칭(Wet Chemical Etching)에 따른 표면변화 특성 및 최적의 에칭 조건을 조사하였다. AlN 웨이퍼를 <TEX>$350^{\circ}C$</TEX>에서 5분간 에칭 시 Al-face, N-face는 서로 다른 관찰되었다. 특히, Al-face는 에치핏의 형상을 파악하여 결함특성을 관찰하였고, 이로부터 결함 밀도를 계산하여 <TEX>$2{\times}10^6/cm^2{\sim}10^{10}/cm^2$</TEX>의 결과를 얻었다. N-face의 경우 육각 뿔(hexagonal pyramids) 형태의 격자결함이 형성되었다. 또한 AlN 웨이퍼의 성장 시 배향을 관찰하기 위해 XRD(X-Ray Diffraction, Rigaku, JAPAN)를 이용하여 분석한 결과 육방정 AlN의 C축 방향에 해당되는 (0002) 및 (0004) 면으로 배향된 상태임을 알 수 있었고, DC-XRD(Double Crystal X-ray Diffraction, bruker, Germany)를 이용하여 rocking curve의 위치에 따라 곡률 반경을 측정했을 때 1.6~17 m의 곡률을 가지고 있는 것으로 나타났다. We investigated the optimal etching conditions and properties of the surface change due to molten KOH/NaOH chemical wet etching using an AlN wafer which has been put to practical use in the present study. Results were observed using a scanning electron microscope after 5 minutes etching at <TEX>$350^{\circ}C$</TEX>, was found to have a surface form of the respective other Al-face, the N-face. In particular, etch-pit in the form of a hexagon, which is observed in the Al-face appeared, It was calculated at <TEX>$2{\times}10^6/cm^2{\sim}10^{10}/cm^2$</TEX> dislocation density. In the case of N-face, lattice defects in the form of the hexagonal pyramids is formed. It was discovered that in order to observe the orientation of the wafer, which corresponds to the C-axis direction of the resulting hexagonal AlN which was analyzed using XRD (0002) and is a state of being oriented in the (0004) plane. The Radius of curvature of AlN wafer was 1.6~17 m measured by DC-XRD rocking curve position.

High performance 380-nm ultraviolet light-emitting-diodes with 3% efficiency droop by using free-standing GaN substrate manufacturing from GaAs substrate

We investigated the influence of free-standing GaN (FS-GaN) substrates on the performance of ultraviolet light-emitting-diodes (UV-LEDs) grown on top by atmospheric pressure metal-organic chemical vapor deposition. High-resolution double-crystal x-ray diffraction (HRDCXD) analysis demonstrated high-order satellite peaks and clear fringes between them for UV-LEDs grown on the FS-GaN substrate, from which the interface roughness was estimated. In addition, the full width at half maximum of the HRDCXD rocking curve in the (0002) and the (101¯2) reflections were reduced to below 90 arc sec. The Raman results indicated that the GaN-based epilayer of strain free was grown. Additionally, the effect of the FS-GaN substrate on the crystal quality of the UV-LEDs was examined in detail by transmission electron microscopy (TEM). The TEM characterizations revealed no defects and V-pits were found in the scanned area. Based on the results mentioned above, the light output power of UV-LEDs on the FS-GaN substrate can be enhanced drastically by 80% and 90% at 20 and 100 mA, respectively. Furthermore, an ultralow efficiency degradation of about 3% can be obtained for the UV-LEDs on the FS-GaN substrate at a high injection current. The use of an FS-GaN substrate is suggested to be effective for improving the emission efficiency and droop of UV-LEDs grown thereon.

Hot Wall Epitaxy(HWE)법에 의한 BaIn2Se4에피레어 성장과 가전자대 갈라짐에 대한 광전류 연구

A stoichiometric mixture of evaporating materials for BaIn2Se4 epilayers was prepared from horizontal electric furnace. To obtain the single crystal thin films, BaIn2Se4 mixed crystal was deposited on thoroughly etched semi-insulating GaAs(100) substrate by the Hot Wall Epitaxy (HWE) system. The source and substrate temperatures were 620 o C and 400 o C, respectively. The crystalline structure of the epilayers was investigated by the photoluminescence and double crystal X-ray diffraction (DCXD). The carrier density and mobility of BaIn2Se4 epilayers measured from Hall effect by van der Pauw method are 8.94×10 17 cm -3 and 343 cm 2 /vs at 293 K, respectively. The temperature dependence of the energy band gap of the BaIn2Se4 obtained from the absorption spectra was well described by the Varshni's relation, Eg(T)=2.6261 eV-(4.9825×10 -3 eV/K)T 2 /(T+558 K). The crystal field and the spin-orbit splitting energies for the valence band of the BaIn2Se4 have been estimated to be 116 meV and 175.9 meV, respectively, by means of the photocurrent spectra and the Hopfield quasicubic model. These results indicate that the splitting of the Δso definitely exists in the states of the valence band of the BaIn2Se4/ GaAs epilayer. The three photocurrent peaks observed at 10 K are ascribed to the A1-, B1-exciton for n = 1 and C21-exciton peaks for n=21.

GaSb: A New Alternative Substrate for Epitaxial Growth of HgCdTe

In this work, GaSb is proposed as a new alternative substrate for the growth of HgCdTe via molecular beam epitaxy (MBE). Due to the smaller mismatch in both lattice constant and coefficient of thermal expansion between GaSb and HgCdTe, GaSb presents a better alternative substrate for the epitaxial growth of HgCdTe, in comparison to alternative substrates such as Si, Ge, and GaAs. In our recent efforts, a CdTe buffer layer technology has been developed on GaSb substrates via MBE. By optimizing the growth conditions (mainly growth temperature and VI/II flux ratio), CdTe buffer layers have been grown on GaSb substrates with material quality comparable to, and slightly better than, CdTe buffer layers grown on GaAs substrates, which is one of the state-of-the-art alternative substrates used in growing HgCdTe for the fabrication of mid-wave infrared detectors. The results presented in this paper indicate the great potential of GaSb to become the next generation alternative substrate for HgCdTe infrared detectors, demonstrating MBE-grown CdTe buffer layers with rocking curve (double crystal x-ray diffraction) full width at half maximum of ∼60 arcsec and etch pit density of ∼106 cm−2.

Piezoelectric La3Ga5.3Ta0.5Al0.2O14 crystal: growth, crystal structure perfection, piezoelectric, and acoustic properties

A five-component crystal of lanthanum–gallium silicate group La3Ga5.3Ta0.5Al0.2O14 (LGTA) was grown by the Czochralski method. The LGTA crystal possesses unique thermal properties and substitution of Al for Ga in the unit cell leads to a substantial increase of electrical resistance at high temperatures. The unit cell parameters of LGTA were determined by powder diffraction. X-ray topography was used to study the crystal structure perfection: the growth banding normal to the growth axis were visualized. The independent piezoelectric constants d 11 and d 14 were measured by X-ray diffraction in the Bragg and Laue geometries. Excitation and propagation of surface acoustic waves were studied by the double-crystal X-ray diffraction at the BESSY II synchrotron radiation source. The analysis of the diffraction spectra of acoustically modulated crystals permitted the determination of the velocity of acoustic wave propagation and the power flow angles in different acoustic cuts of the LGTA crystal.

뜨거운 곁쌓기 법에 의해 성장된 MgGa2Se4단결정 박막의 열처리 효과

The evaporating materials for single crystal thin films was prepared from horizontal electric furnace. To obtain the single crystal thin films, compounded polycrystal powder was deposited on thoroughly etched semi-insulated GaAs(100) substrate by the hot wall epitaxy (HWE) method system. The source and substrate temperatures of optimized growth conditions, were and , respectively.The source and substrate temperatures were and , respectively. The crystalline structure of the single crystal thin films was investigated by double crystal X-ray diffraction (DCXD). The temperature dependence of the energy band gap of the obtained from the absorption spectra was well described by the Varshni`s relation, $E_g(T)

Epitaxial growth of GaN by radical-enhanced metalorganic chemical vapor deposition (REMOCVD) in the downflow of a very high frequency (VHF) N2/H2 excited plasma – effect of TMG flow rate and VHF power

Gallium nitride (GaN) films have been grown by using our newly developed Radical-Enhanced Metalorganic Chemical Vapor Deposition (REMOCVD) system. This system has three features: (1) application of very high frequency (60MHz) power in order to increase the plasma density, (2) introduction of H2 gas together with N2 gas in the plasma discharge region to generate not only nitrogen radicals but also active NHx molecules, and (3) radical supply under remote plasma arrangement with suppression of charged ions and photons by employing a Faraday cage. Using this new system, we have studied the effect of the trimethylgallium (TMG) source flow rate and of the plasma generation power on the GaN crystal quality by using scanning electron microscopy (SEM) and double crystal X-ray diffraction (XRD). We found that this REMOCVD allowed the growth of epitaxial GaN films of the wurtzite structure of (0001) orientation on sapphire substrates with a high growth rate of 0.42μm/h at a low temperature of 800°C. The present REMOCVD is a promising method for GaN growth at relatively low temperature and without using costly ammonia gas.

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

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

Hot Wall Epitaxy(HWE)법에 의한 MgGa2Se4 단결정 박막 성장과 가전자대 갈라짐에 대한 광전류 연구

A stoichiometric mixture of evaporating materials for single crystal thin films was prepared from horizontal electric furnace. To obtain the single crystal thin films, mixed crystal was deposited on thoroughly etched semi-insulating GaAs(100) substrate by the Hot Wall Epitaxy (HWE) system. The source and substrate temperatures were and , respectively. 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 thin films measured from Hall effect by van der Pauw method are and at 293 K, respectively. The temperature dependence of the energy band gap of the obtained from the absorption spectra was well described by the Varshni's relation, . The crystal field and the spin-orbit splitting energies for the valence band of the have been estimated to be 182.7 meV and 42.6 meV, respectively, by means of the photocurrent spectra and the Hopfield quasicubic model. These results indicate that the splitting of the definitely exists in the states of the valence band of the epilayer. The three photo current peaks observed at 10 K are ascribed to the , for n = 1 and peaks for n = 27.

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.

Suppressing the spread length of threading dislocations in AlSb/GaSb superlattice grown on (001) InP substrate

Two designed structures of ternary Al0.5Ga0.5Sb and AlSb/GaSb superlattice (SL) buffers were prepared by molecular beam epitaxy. Double crystal X-Ray diffraction (XRD) and transmission electron microscopy (TEM) were used to characterize the material quality and observe the threading dislocation (TD) spreading behaviors. It was found that despite the wider full width at half-maximum (FWHM) of the w-rocking curve obtained in the SL buffer compared with the AlGaSb buffer, the stronger the TD filter ability enabled the SL buffer to block the defects to beneath the thickness around 500 nm. This result suggests the AlSb/GaSb SL buffer possessed the superiority in the fabrication of antimony (Sb) based microelectronic devices.

Three-step growth of metamorphic GaAs on Si(001) by low-pressure metal organic chemical vapor deposition

In this study, metamorphic growth of GaAs on Si(001) substrate was investigated via three-step growth in a low-pressure metal organic chemical vapor deposition reactor. Three-step growth was achieved by simply inserting an intermediate temperature GaAs layer between the low temperature GaAs nucleation layer and the high temperature GaAs epilayer. Compared with conventional two-step growth, three-step growth could further reduce surface roughness and etch pit density. By combining three-step growth with thermal-cycle annealing, the authors have grown a 1.8-μm-thick GaAs epilayer with root mean square roughness of only 1.8 and 0.73 nm in 10 × 10 μm2 and 2 × 2 μm2 scanning areas, respectively. The threading dislocation density of the 1.8-μm-thick GaAs epilayer was as low as 1.1 × 107 cm−2, as calculated directly from the double crystal x-ray diffraction ω-scan full width at half maximum of the GaAs diffraction peak. The corresponding etch pit density was only 3 × 106 cm−2.

Postgrowth Annealing of CdTe Layers Grown on Si Substrates by Metalorganic Vapor-Phase Epitaxy

Annealing conditions of CdTe layers grown on Si substrates by metalorganic vapor-phase epitaxy were studied. Typically, 3-μm-thick n-type (211) CdTe layers were annealed for 60 s in flowing hydrogen at atmospheric pressure by covering their surfaces with bulk CdTe wafers. At annealing temperatures above 700°C, improvement of crystal quality was confirmed from full-width at half-maximum values of double-crystal rocking-curve measurements and x-ray diffraction measurements. Photoluminescence measurements revealed no deterioration of electrical properties in the annealed n-CdTe layers. Furthermore, annealing at 900°C improved the performance of radiation detectors with structure of p-like CdTe/n-CdTe/n+-Si substrate.

The structural and magnetic properties of Fe/(Ga, Mn)As heterostructures

Fe/(Ga, Mn)As heterostructures were fabricated by all molecular-beam epitaxy. Double-crystal X-ray diffraction and high-resolution cross-sectional transmission electron micrographs show that the Fe layer has a well ordered crystal orientation and an abrupt interface. The different magnetic behavior between the Fe layer and (Ga, Mn)As layer is observed by superconducting quantum interference device magnetometry. X-ray photoelectron spectroscopy measurements indicate no Fe2As and Fe—Ga—As compounds, i.e., no dead magnetic layer at the interface, which strongly affects the magnetic proximity and the polarization of the Mn ion in a thin (Ga, Mn)As region near the interface of the Fe/(Ga, Mn)As heterostructure.

Stress State of GaN Epilayer Grown on Sapphire and 6H-SiC Substrates

Abstract The stress states and influence of two opposite stress types under similar stress intensities on the structural and optical properties of GaN films grown on sapphire and 6H-SiC substrates via metalorganic chemical vapor deposition were investigated. The E2 (high) phonon shifts of Raman spectra show that tensile stresses exist in the GaN epilayer grown on 6H-SiC, whereas compressive stresses appear in the film grown on sapphire, indicating that the thermal mismatch between the epilayers and the substrates plays a major role in determining the residual stresses in GaN films. Narrower full widths at half-maximum of E2 (high) phonon and double crystal X-ray diffraction peaks and the higher E2 (high) phonon intensity are visible for the GaN film grown on sapphire, illustrating that under almost equivalent stress intensities, tensile stresses have a much more negative influence on the crystalline quality of GaN epilayers. Finally, a numerical relationship between the luminescent band gap and the biaxial stresses of the GaN films is obtained at 10 K.