Resolution X-ray Diffraction Reciprocal Space Research Articles

Growth of highly relaxed InGaN pseudo-substrates over full 2-in. wafers

A highly relaxed InGaN buffer layer was demonstrated over a full two-inch c-plane sapphire substrate by metalorganic chemical vapor deposition. The InGaN buffer layer was grown on a 100 nm GaN decomposition stop layer with a 3 nm thick high indium composition InGaN underlayer. After thermal decomposition of the underlayer at 1000 °C, a 200 nm thick In0.04Ga0.96N buffer showed 85% biaxial relaxation measured by a high resolution x-ray diffraction reciprocal space map. When used as a pseudo-substrate for the regrowth of InGaN/InGaN multi-quantum wells, the sample showed a 75 nm red-shift in room temperature photoluminescence when compared to a co-loaded GaN template reference. The longer emission wavelength is associated with higher indium incorporation in the InGaN layers from the lessening of the compositional pulling effect caused by compressive strain. Using this technique, a simple red light emitting diode was demonstrated with an active layer growth temperature of 825 °C and a peak wavelength of 622 nm at a current density of 20 A cm−2. This work represents a unique method to relax a III-nitride based layer over a full substrate.

Fabrication of relaxed InGaN pseudo-substrates composed of micron-sized pattern arrays with high fill factors using porous GaN

Fully or partially relaxed micron-sized InGaN patterns with fill factors up to 69% were demonstrated via porosification of the underlying GaN:Si layer. The impact of the porosification etch conditions and the pattern geometry on the degree of InGaN relaxation were studied and monitored via high resolution x-ray diffraction reciprocal space maps. Additionally, a 45 nm redshift in the photoluminescence emission from InxGa1−xN/ InyGa1−yN multi-quantum wells (MQWs) regrown on bi-axially relaxed InGaN buffer layers was observed when compared to a co-loaded reference sample grown on GaN. The longer emission wavelength was associated with higher indium incorporation into the InGaN layers deposited on the InGaN base layers with a lattice constant larger than GaN, due to the reduced lattice mismatch between MQW and InGaN base layer, also called compositional pulling effect.

Structural and chemical investigation of interface related magnetoelectric effect in Ni/BiFe0.95Mn0.05O3 heterostructures

The magnetoelectric coupling mechanism in Ni/BiFe0.95Mn0.05O3 heterostructures is investigated through a detailed microstructural study of the BiFe0.95Mn0.05O3 film and a chemical analysis of the Ni/BiFe0.95Mn0.05O3 interface. The four structural variants expected in BiFe0.95Mn0.05O3 are detected by high resolution X-ray diffraction reciprocal space mapping method. The ferroelectric domain structure is imaged with transmission electron microscopy. Oxidized Ni is evidenced at the Ni/BiFe0.95Mn0.05O3 interface by electron energy loss spectroscopy and X-ray photoemission spectroscopy, although the degree of Ni oxidation is independent of the magnetoelectric state of the heterostructure.

Optimization of In0.6Ga0.4As/InAs electron barrier for In0.74Ga0.26As detectors grown by molecular beam epitaxy

The effects of thickness and period number of In0.6Ga0.4As/InAs superlattice electron barrier on the performances of InP-based metamorphic In0.74Ga0.26As detectors have been investigated. The samples were grown by molecular beam epitaxy and characterized by high resolution X-ray diffraction reciprocal space maps, photoluminescence, atomic force microscope, plan view transmission electron microscopy and the device dark current measurements. Results show that the dark currents are reduced by insertion of an electron barrier with moderate thickness and period number in the absorption layer, but a superlattice electron barrier structure with excessive thickness and period number can lead to the deterioration of the material quality and device performances.

Epitaxial LaFeO3 and LaFe0.75Zn0.25O3 thin films on SrTiO3 (STO) (100) substrate: Structural studies and high energy magnon excitations

The epitaxial films of LaFeO3 (LFO) and LaFe0.75Zn0.25O3 (LFZO) are grown on a SrTiO3 (STO) (100) substrate using pulsed laser deposition. The as-grown films have been investigated to study the structural properties and magnon excitations using temperature dependent Raman spectroscopy. X-ray diffraction and high resolution x-ray diffraction reciprocal space mapping indicate the epitaxial growth of films on the STO (100) substrate. RSM shows the broadening of the diffraction spot in the qz direction that may be due to the tilt present in the thin films, suggesting the orthorhombic growth of the films. Raman measurements on LFO and LFZO thin films have been performed for structure identification. The absence of first order phonon modes in Raman spectra suggests that the structure of films is symmetric and is coherent with the cubic substrate. High energy Raman bands with typical characteristics of two-magnon scattering appear below Neel temperature. Splitting of magnon branches is seen for both LFO and LFZO films and has been analyzed on the basis of the magnetic structure of LFO. The hardening of the magnon modes is observed as the temperature approaches towards the Neel temperature that may be attributed to the lattice contraction and correlated with a decrease in the tilt and a corresponding increase in the Heisenberg exchange constant (J) leading to a more ordered state at Neel temperature.

XBaTiO3–(1−x)BiFeO3 strained epitaxial thin film with enhanced magnetization

Strained epitaxial xBaTiO3–(1−x)BiFeO3 (x=0–0.2) thin films were grown on STO (001) substrate by radio frequency magnetron sputtering. The crystal structure of the as-deposited thin films were investigated using the combination of powder X-ray diffraction (XRD) and high resolution X-ray diffraction reciprocal space mapping (HRXRD–RSM). The relationship of the crystal structure and magnetic properties of the as-deposited thin films was also investigated. The larger c/a values provide the iron ion with a non-vanished orbital quenching effect, which produces the strong spin-orbital coupling that suppresses the spiral spin structure and initiates a canted antiferromagnetic phase with larger magnetizations at room temperature.

Progress in large area organometallic vapor phase epitaxy for III–V multijunction photovoltaics

Multijunction solar cells are fabricated using organometallic vapor phase epitaxy (OMVPE) to deposit subcells of GaInP and GaInAs on 150mm diameter Ge substrates. We review the general challenges of achieving solar cell epitaxial growth on 150mm dia. Ge and discuss basic GaInP material characterization. Metamorphic GaInP/GaInAs/Ge C4MJ epitaxial layers are characterized by in-situ curvature measurements during growth. A 98.5% relaxation is measured by high resolution X-ray diffraction reciprocal space mapping, and a threading dislocation density of 1.3×105cm−2 is measured by cathodoluminescence in active regions of the device. Test batches of 20kWp of cells, 1.0cm2 in aperture area, are grown and fabricated on 100mm and 150mm dia. Ge wafers and average 40.2% and 40.1% efficiency, respectively, under 50W/cm2 AM1.D illuminated current–voltage (LIV) testing. Finally, we demonstrate very large area, >72cm2, triple junction XTJ space devices, averaging 29.3% efficiency for 73 such devices under space LIV testing (0.1353mW/cm2, 28°C, AM0).

X-ray diffraction analysis of step-graded InxGa1−xAs buffer layers grown by molecular beam epitaxy

High resolution X-ray diffraction reciprocal space mapping (RSM) is used to study the crystal quality of step-graded InxGa1−xAs buffer layers grown on GaAs (001) substrates by molecular beam epitaxy (MBE) using two growth methods. The lateral correlation length of the buffer layers are described by the FWHM of diffraction peaks along the lateral directions extracted from RSM, which are good indicators of the layer's crystalline quality. The quality improvement of InxGa1−xAs buffer layers grown at low temperature with in-situ annealing could be determined by XRD-RSM, which is also consistent with TEM results.

Domain structures in epitaxial Pb(Zr 0.68,Ti 0.32)O 3 thin films

Domain structures and their volume fractions in (0 0 1)-, (1 0 1)- and (1 1 1)-oriented epitaxial Pb(Zr 0.6,Ti 0.4)O 3 (PZT) films grown on (0 0 1), (1 1 0) and (1 1 1) SrTiO 3 (STO) single crystal substrates, respectively, were characterized by using a high resolution X-ray diffraction reciprocal space mapping (RSM) technique. The results of RSM revealed the presence of (1 0 1 ̄ ) and (1 1 1 ̄ ) orientation as well as (1 1 0) and (1 1 1) orientations for the films grown on (1 1 0) and (1 1 1) STO substrates, respectively, although (0 0 1)-oriented film had (0 0 1)-oriented simple domain structure. These multiple domain configurations seemed to be introduced by {1 0 0} and {1 0 1} twin domain boundaries. The RSM analysis also showed that the relative volume fractions of (1 0 1 ̄ ) and (1 1 1 ̄ ) orientations were 22% and 52% against (1 1 0) and (1 1 1) orientations, respectively.