Simulation of X-Ray Diffraction Spectra for AlN/GaN Multiple Quantum Well Structures on AlN(0001) with Interface Roughness and Variation of Vertical Layers Thickness

A detailed XRD analysis of AlN/GaN multiple quantum well (MQW) structures grown on AlN(0001) substrates is proposed. The effect of roughness on the 2θ-ω scans measured in Bragg diffraction for symmetrical reflections is investigated together with the effect of depth variation of the well and barrier thickness. As shown, the magnitude of depth variation of the well and barrier thickness results in an asymmetrical broadening of the satellite peaks of the 2θ-ω scans. Roughness causes their symmetrical expansion that allows separating the influence of both effects. Several reasons of asymmetrical broadening of satellite peaks are considered: variation of the thickness period, variation of the average lattice parameter inherent to the period, which depends on the thickness ratio of the layers in the period, and their combination. The efficiency of the described method is illustrated in detail by numerical simulations.В работе предложен детальный рентгенодифракционный анализ структур с множественными квантовыми ямами (МКЯ) AlN/GaN, выращенными на подложках AlN(0001). Было исследовано влияние шероховатости и вариации толщины слоёв квантовых ям и барьеров на 2θ-ω-сканы, полученные в геометрии отражения по Брэггу для симметричных рефлексов. Показано, что наличие вариации толщины слоёв AlN и GaN по глубине приводит к появлению асимметрии сателлитных пиков МКЯ на 2θ-ω-сканах. Наличие шероховатости приводит к симметричному расширению сателлитных пиков, что позволяет разделить влияние этих эффектов. Рассмотрено несколько причин асимметричного расширения сателлитных пиков: изменение толщины периода, изменение среднего параметра решётки периода, который зависит от соотношения толщин слоёв в периоде, и их комбинации. Эффективность разработанного метода показана с помощью численного моделирования.В роботі проведено детальну аналізу структур із множинними квантовими ямами (МКЯ) AlN/GaN, вирощених на підкладинках AlN(0001). Було досліджено вплив шерсткости та зміни товщини шарів структури з МКЯ по глибині на 2θ-ω-скани, виміряні в Бреґґовій геометрії дифракції для симетричних рефлексів. Показано, що зміна товщини квантових ям і бар’єрів по глибині приводить до асиметричного розширення сателітних піків МКЯ на 2θ-ω-сканах. Шерсткість спричинює симетричне розширення піків, що уможливлює розрізнити вплив цих ефектів. Розглянуто кілька причин асиметричного розширення сателітних піків: зміну товщини періоду, зміну середнього параметра ґратниці періоду, який залежить від співвідношення товщин шарів періоду, та їх комбінації. Ефективність розробленої методи показано шляхом числового моделювання рентґенівських спектрів

Study of Structure and Intrinsic Stresses of Ge Thin Films on GaAs

The effect of film growth rate on the structure and intrinsic stresses of thin (100 nm) Ge films grown on GaAs(100) substrates was investigate by High Resolution X-Ray Diffraction (HRXRD). The Ge films were deposited onto GaAs using thermal evaporation of Ge in the vacuum. It was shown that pseudomor-phic films with good structural quality can be obtained by this growth technique. We found out that the films have biaxial deformations due to coherent interface and Poisson ratio. The films are elastically com-pressed in the interface and stretched in the perpendicular [001] direction. The intrinsic deformations of thin Ge films strongly depended on the deposition rate. Their correlations with surface roughness, electri-cal and optical parameters are discussed. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3531

X-ray diffraction investigation of GaN layers on Si(111) and Al₂O₃ (0001) substrates

Methodical approaches to the analysis of X-ray data for GaN films grown on various buffer layers and different substrates are presented in this work. Justification of dislocation structure investigation by various methods was analyzed and approaches for evaluation of deformation level and relaxation are discussed. Clarity and accuracy of obtained structure characteristics of nitride films are under discussion. Optimization methods for experimental data processing are shown. Structural properties were obtained using high resolution X-ray diffraction with two types of scans and reciprocal space maps. Microscopic nature of spatial inhomogeneities in these structures (deformations and dislocation density) and influence of the buffer layer thickness on properties of GaN layer were discussed with account of obtained results

Anisotropy of elastic deformations in multilayer (In,Ga)As/GaAs structures with quantum wires: X-ray diffractometry study

Using the method of high-resolution X-ray diffraction (HRXRD), we have studied 17-period In₀.₃Ga₀.₇As/GaAs multilayer structure with self-assembled quantum wires (QWRs) grown by the MBE and subjected to postgrowth rapid thermal annealing (RTA) at temperatures (Tann) from 550 to 850 °C for 30 s. It has been shown that the spatial arrangement of QWRs (lateral and vertical) causes the quasi-periodical strain distribution, the strains being essentially anisotropic relatively to crystallographic directions of 〈011〉 type. At Tann ≤ 750 °С, the driving mechanism of structural transformations is relaxation of residual strains due to thermally-activated and strain-enhanced processes of In/Ga atom interdiffusion at the interface QWRs-2D layer, which does not result in considerable changes of the In concentration in (In,Ga)As QWRs. The presence of two superlattice vertical periods in the samples under study and their changes during RTA we explained by an anisotropic character of elastic strain distribution and lowered structure symmetry. The revealed increase in the (In,Ga)As QWRs lateral period caused by RTA is a direct evidence of running lateral mass-transfer processes and can be explained using the model “nucleation plus strain-enhanced In/Ga atom lateral interdiffusion”. At low annealing temperatures, there takes place dissolution of intermediate QWRs as a result of interdiffusion enhanced by residual anisotropic strains. At high RTA temperatures, the interdiffusion process is mainly determined by the composition gradient existing between QWRs and 2D layer

Властивості високодисперсних систем на основі телуриду кадмію, отриманих шляхом електрохімічного диспергування

Physical and chemical properties of highly dispersed systems on the base of metallic (cadmium, tellurium) and semiconductor materials (cadmium telluride) obtained by the plasma-electrochemical method are studied. It is shown that obtained systems consist of particles of different sizes, and in some cases there are two polymorphic modifications of the systems. Досліджено фізико-хімічні властивості високодисперсних систем на основі металічних (кадмій, телур) та на основі напівпровідникових матеріалів (кадмій телурид), отриманих плазмоелектрохімічним методом. Показано, що отримані системи складаються з частинок різного розміру, а в окремих випадках існують в двох поліморфних модифікаціях.&nbsp

Deformation state of short-period AlGaN/GaN superlattices at different well-barrier thickness ratios

Dependence of deformation characteristics changing in superlattice (SL) structures AlxGa₁₋xN/GaN with Al (~10%) on the well-barrier thickness ratio in period was studied in this work. The deformation state of SL and individual layers, relaxation level and periods, layers’ thickness and composition of AlxGa₁₋xN layers were analyzed using high-resolution X-ray diffractometry. It was ascertained that the buffer layer and SL layers are compressed in all the investigated structures. Thus, it has been shown that deformation of the SL period depends on the well/barrier thickness ratio. Thicknesses of individual layers in SL strongly depend on the deformation state of the whole system. Increasing the deformation level leads to the increase of the barrier layer thickness

X-ray diffraction study of deformation state in InGaN/GaN multilayered structures

High resolution X-ray diffractometry (HRXRD) was used to investigate InxGa₁₋xN/GaN multilayered structures grown by the metal-organic chemical vapor deposition (MOCVD) method. Deformation conditions in the superlattice (SL) and its separate layers, degree of relaxation in the structure layers, as well as the period of the SL, thicknesses of its layers and composition of InxGa₁₋x solid solution in active area were determined. It was found that SL was grown on the relaxed buffer layer. SL layers were grown practically coherent with slight relaxation of InGaN layer (about 1.5 %). The role of dislocations in relaxation processes was established. Analysis of experimental diffraction spectra in these multilayered structures within the frameworks of ParratSperiozu was adapted for hexagonal syngony structures

Modification of properties of the glass-Si₃N₄-Si-SiO₂ structure at laser treatment

We studied the effect of laser treatment on the glass-Si₃N₄-Si-SiO₂ structures. It is shown that laser treatment causes appearance of an additional band in their transmission spectra as well as smearing of grain structure at their surface

Structural changes in Cz-Si single crystals irradiated with high-energy electrons from data of high-resolution X-ray diffractometry

Structural changes in silicon single crystals irradiated with high-energy electrons (Е = 18 MeV) were studied. The peculiarities of diffraction reflection curve behaviour and changes in the profiles of isodiffusion lines in high-resolution reciprocal space maps (HR-RSMs) were found as a function of the radiation dose. The generalized dynamic theory of X-ray Bragg-diffraction in crystals comprising defects of several types (spherical and disc-shaped clusters as well as dislocation loops) and a damaged nearsurface layer was used for explanation

Heat-resistant barrier and ohmic contacts based on TiBx and ZrBx interstitial phases to microwave diode structures

We investigated thermal stability of Au–TiBx (ZrBx) barrier contacts, as well as ohmic contacts with a TiBx diffusion barrier to n-Si (GaAs, InP, GaP, GaN, SiC). The electrophysical measurements of Schottky barrier diodes and ohmic contacts were performed both before and after rapid thermal annealing (RTA) up to 600 °С for the structures on Si, GaAs, InP and GaP, as well as up to higher temperatures for GaN (~900 °C) and SiC (~1000 °C). The concentration depth profiles of contact components were taken using Auger electron spectrometry, while phase composition and surface morphology of the metallization layers on test structures were determined using x-ray diffraction and atomic force microscopy. It was shown that the silicon, indium phosphide, gallium phosphide and gallium arsenide contact structures retained their properties and layer structure after RTA up to 600 °С. Contact degradation occurred at a temperature of 800 °С. The structures based on SiC (GaN) remained stable at temperatures up to 1000 °С (900 °С)