High-resolution X-ray Diffraction Mapping Research Articles

Hybrid epitaxy technique for the growth of high-quality AlInAs and GaInAs layers on InP substrates

The quality and properties of epitaxial films are strongly determined by the reactor type and the precursor source phase. Such parameters can impose limitations in terms of background doping, interface sharpness, clustering, phase separation, and homogeneity. The authors have implemented a hybrid epitaxy technique that employs, simultaneously, vapor and solid sources as group III precursors. The system combines the high throughput and the versatility of gas sources as well as the high purity of solid sources. Using this technique, the authors successfully demonstrated epitaxial growth of Al0.48In0.52As and Ga0.47In0.53As layers on Fe-doped semi-insulating InP (001) substrates with interesting properties, compared with the epilayers grown by more standard techniques (chemical beam epitaxy, metal-organic chemical vapor deposition, and MBE). For AlInAs growth, trimethylindium and solid aluminum were used as In and Al precursors, respectively. In the case of GaInAs, triethylgallium and solid indium were used, respectively, as Ga and In precursors. Thermally cracked arsine (AsH3) was used as an As (group V) precursor for both alloys. The AlInAs and GaInAs epilayers grown at a temperature of 500 °C exhibited featureless surfaces with RMS roughness of 0.2 and 1 nm, respectively. Lattice mismatch is of 134 ppm, for AlInAs, and −96 ppm, for GaInAs, which were determined from high-resolution x-ray diffraction (HR-XRD) patterns and showed a large number of Pendellösung fringes, indicating a high crystalline quality. An FWHM of 18.5 arcs was obtained for GaInAs epilayers, while HR-XRD mapping of a full 2-in. wafer confirmed a viable lattice mismatch homogeneity (standard deviation of 0.026%) for as-grown layers. The authors observed room-temperature background doping values as low as 3 × 1015 cm−3, for AlInAs, and 1 × 1015 cm−3, for GaInAs. Analysis of the PL spectra at 20 K showed an FWHM of 8 meV, for AlInAs, and 9.7 meV, for GaInAs, demonstrating a very good optical quality of the epilayers. In addition, they have investigated the effects of the growth temperature and of the arsine pressure on epilayer properties. They also discuss the optimum conditions for the growth of high-quality Al0.48In0.52As and Ga0.47In0.53As layers on InP (001) substrates using this hybrid epitaxy technique.

Investigation of defect structure of InGaNAsSb/GaAs quantum wells

The results of the photoluminescence (PL) and the high-resolution X-ray diffraction (HRXRD) investigations of point and extended defects in strained InGaAs(N)Sb/GaAs quantum well (QW) structures grown at 478–505 °C are presented. HRXRD studies prove a good quality of heterointerfaces in all samples that is attributed to Sb-surfactant effect. The PL investigations show that the increase of the growth temperature of N-containing QWs leads to the increase of potential fluctuations in QW due to the increase of composition disorder. In the PL spectra an intense band caused by excitonic transitions related with N-related clusters in GaAs barriers is found. HRXRD mapping in symmetrical 004 reflections reveals the oscillation of interference picture in [110] direction around the normal to (100) surface known as a “wiggle”. The mapping indicates the formation of elastically coupled domains which are elongated in [¯110] direction and are supposed to be cased by lateral composition modulations in the QW. It is proposed that a “wiggle” explained by the change of slopes of crystallographic planes with the depth is the result of competition of two factors — a symmetry of the surface stress tensor and a symmetry of bulk elastic moduli of a substrate material.

Epitaxial PbTiO3 Thin Films on SrTiO3(100) and SrRuO3/SrTiO3(100) Substrates Deposited by a Hydrothermal Method

Lead titanate (PbTiO3) thin film is a promising material for ultrahigh-density ferroelectric data storage systems, pyroelectric sensors and ferroelectric optical devices. In this study, high-quality epitaxial PbTiO3 thin films were deposited on SrTiO3(100) and SrRuO3/SrTiO3(100) by a hydrothermal method. The crystal orientation of the deposited film was investigated with a high-resolution X-ray diffraction mapping system. The full width at half maximum (FWHM) of the rocking curve of the (002) PbTiO3 film on SrTiO3 was 0.060°. The reciprocal space mappings of (103) verified that the PbTiO3 films had perfect c-axis orientation. The self-aligned polarization was confirmed with observation using a scanning nonlinear dielectric microscope. The PbTiO3 on SrRuO3/SrTiO3(100) was used for the D-E hysteresis curve measurement and the remanent polarization was 96.5 µC/cm2. Domain patterning was applied to a 50-nm-thick PbTiO3 film using a conductive cantilever probe. The minimum radius of the nano domain dot was 12 nm, corresponding to a data density of 1 Tbit/inch2.

Polar and nonpolar GaN grown by HVPE: Preferable substrates for nitride-based emitting devices

We report on hydride vapor phase epitaxial growth of thick nonpolar GaN films on r-plane sapphire in comparison with polar GaN films on c-plane sapphire substrates with AlN buffer layers, aiming at developing of their quasi-substrate application. Both the thick films and the buffers were identified to have single crystalline structures. The microstructure of the films was studied by transmission electron microscopy. High resolution X-ray diffraction mapping and photoluminescence measurements were employed to characterize the strain present in both polar and nonpolar GaN films. In contrast to c-plane GaN, which is always characterised by isotropic in-plane properties, the a-plane GaN shows a strong in-plane anisotropy of the growth rate, morphology and strain distribution. Different defect, impurity and free carrier concentrations were observed in the polar and nonpolar material. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Investigation of the relaxation behaviour of epitaxially grown wire structures by means of Monte‐Carlo‐Simulation

We present results on the elastic relaxation behaviour of II-VI and III-V wire structures. The structures were obtained by wet etching of extended layers as well as shadow mask assisted Selected Area Epitaxy (SAE). The SAE wire structures are especially interesting since they are grown directly, do not require treatment after the growth process, and posess the ability to relax elastically during growth. Reciprocal space maps of strained semiconductor structures, obtained by High Resolution X-ray Diffraction (HRXRD) have so far been interpreted in the context of bulk elastic properties. In this contribution we introduce a relaxation procedure based on interatomic potentials. The wire structure is simulated with atomic resolution atop of the substrate material. A Monte-Carlo algorithm is applied to relax the structure while minimizing the strain energy. The reciprocal space maps calculated from the relaxed structure are in good agreement with the observed HRXRD maps. Hence we can interprete the strain state of the wire structures with atomic resolution. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Perfectly c-axis oriented epitaxial lead titanate thin film deposited by a hydrothermal method for a data storage medium

ABSTRACTA hydrothermal method is a unique method to deposit ferroelectric thin films utilizing chemical reaction in solutions. In addition to the low reaction temperature below 200°C, its simple process procedure, automatically aligned polarization and a three-dimensional deposition are advantages. In this study, a lead titanate epitaxial thin film was obtained on a strontium ruthenate bottom electrode sputterd on strontium titanate (100). The highresolution X-ray diffraction mapping showed the film was perfectly c-axis oriented. The transmission electron microscope observation revealed that the film had no lattice dislocation at the interface between lead titanate and strontium ruthenate. A remanent polarization of 96.5μC/cm2 was measured with the single crystal-like DE hysteresis curve. The observation of a scanning nonlinear dielectric microscopy indicated that this film did not contain any defect such as an a-domain and a grain boundary even on the nano scale. With various pulse parameters, nano-domain dots were patterned and the minimum dot radius of inverted domain was 12 nm corresponding to data storage density of 1Tbit/inch2.

Phosphorus profile control in low-temperature silicon epitaxy by reduced pressure chemical vapor deposition

Phosphorus incorporation around 10 18 cm −3 has been studied during low-temperature (660–750 °C) silicon epitaxy by chemical vapor deposition under reduced pressure (20 torr) using silane (SiH 4) or dichlorosilane (SiH 2Cl 2) as silicon precursor. Strong surface segregation of phosphorus was observed. The phosphorous segregation could be reduced either by decreasing the growth temperature or adding HCl during growth of the undoped layer. Neither reduced growth temperature nor HCl addition was able to produce steep turn-off of the phosphorus concentration with an acceptable growth rate. Therefore, ex situ removal of the phosphorus surface layer was tested using either a chemical oxidation or a low-temperature thermal oxidation. In both cases, a dramatic reduction in surface segregation was observed with a slope less than 15 nm/decade in the resulting dopant profile. A subsequent epitaxial Si/SiGe (17%) growth on the ex situ cleaned sample was found to result in layers exhibiting high crystalline quality according to high resolution X-ray diffraction mapping.

Reexamination of N composition dependence of coherently grown GaNAs band gap energy with high-resolution x-ray diffraction mapping measurements

GaNAs films grown on GaAs(001) substrates by metalorganic molecular beam epitaxy were studied by high-resolution x-ray diffraction (XRD) mapping measurements. The lattice constants of epitaxial films are usually estimated from symmetric and asymmetric XRD 2θ−θ measurements. In this study, it is pointed out that the consideration of the tilt angle between the GaAs(115) and GaNAs(115) planes caused by elastic deformation of the films is crucial to determine the lattice constants of the GaNAs films coherently grown on GaAs substrates. Mapping measurements of (115) XRD (2θ−θ)−Δω were performed for this purpose. The band gap energy of the films was determined by Fourier transform absorption spectroscopy measurements. The band gap energy bowing measured up to the N composition of 4.5% will be discussed by comparing with other measurements and theoretical calculations.

High resolution X-ray diffraction mapping studies on the domain structure of LaAlO 3 single crystal substrates and its influence on SrTiO 3 film growth

High resolution X-ray diffraction mapping studies have been done on 001-oriented LaAlO 3 substrates and epitaxial 001-oriented SrTiO 3 thin films grown on the LaAlO 3. Using high resolution ω-ω 2θ reciprocal space mapping over the 002 peak, the lattice constant of LaAlO 3 could be accurately determined; however, it was not possible to determine the small splitting of the 002 peak due to the different twin domains. This is due to the poor resolution, inherent from the diffractometer design, for planes perpendicular to the diffraction plane. The pole plot method also makes use of the resolution perpendicular to the diffraction plane and will therefore not resolve the domain either. However, ω-ø mapping has been successfully used to resolve the domain distribution and angles between the domains since it scans the diffraction space in a plane parallel to the sample surface and it has high resolution along the ω direction. It was found that the LaAlO 3 usually contains four domains with four-fold twinning symmetry. The angular separations of the domains were 0.177°, 0.177° and 0.253°. Annealing the sample showed to have a detwinning effect sometimes resulting in a single domain sample. To investigate the influence of the domain structure on the growth of SrTiO 3 films, two kinds of films were studied. For stoichiometric SrTiO 3 film the domain structure of the substrate was exactly copied into the film as revealed by the ω-ω 2θ map and ω-ø maps. On the other hand Sr-deficient film exhibited a large degree of mosaicity and the resulting peak broadening overwhelmed the splitting due to domains.

Combined Room Temperature Photoluminescence And High Resolution X-Ray Diffraction Mapping Of Semiconductor Wafers

AbstractWe describe the characteristics and performance of a combined desk-side high resolution X-ray diffractometer and room temperature photoluminescence spectrometer designed for rapid mapping of compound semiconductors in a production line context. The combined data for AIGaAs on GaAs suggest that recent measurements of the lattice constant and the Poisson ratio of AlAs may be more reliable than earlier published values. We illustrate the instrument performance in showing that for lattice matched ternary GaInP on GaAs systems, the X-ray rocking curve maps are much more sensitive to composition variation than the photoluminescence spectra.

Thermal Stability Characterization of Doped Layers and Heterostructures Grown by Si-Molecular Beam Epitaxy

The thermal stability of layers grown by Si-molecular beam epitaxy is reported in a comparative study of strain induced in Si by heavy B doping and by Si1-x Gex alloying. High-resolution X-ray diffraction mapping was employed as the major analytical tool. The strain relaxation under high-temperature annealing is shown to be dominated by the formation of precipitates and by diffusion in the case of heavy doping but with a negligible amount of dislocations. In the Si1-x Gex /Si heterostructures, the process is dominated by strain relaxation via formation of misfit dislocations.

Strain characterization of CoSi2/n-Si0.9Ge0.1/p-Si heterostructures

We report on the structural characterization of CoSi2/n-Si0.9Ge0.1/p-Si heterostructures. Silicon molecular beam epitaxy is combined with Co sputtering to obtain these structures. The strain in the Si1−xGex is investigated after the formation of the CoSi2 by using high-resolution x-ray diffraction mapping in reciprocal space and cross-sectional transmission electron microscopy. The results show that in order to keep the strain in Si1−xGex unaffected, a sacrificial Si layer is needed. It was possible to obtain transistor action, but with low-current gain (β).

Strain relaxation in epitaxial Si1-xGex layers during some silicidation processes

Strain relaxation in Si1-xGex epitaxial layers is investigated after the reaction of Co and Pt with strained SiGe alloy. The epitiaxial SiGe alloy studied has a Ge fraction ranging between x = 5% to 22%. The strain in the Si1-xGex is evaluated using multi-crystal high resolution x-ray diffraction mapping in reciprocal space (MC-HRXRD). The results show that for Co in order to keep the strain in Si1-xGex unaffected, a sacrificial Si layer is needed. The direct reaction of 40 nm Co on Si0.9Ge0.1 can lead to defect formation and 40% strain relaxation. This is in contrast to Pt/Si1-xGex reaction, where negligible relaxation was observed.