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Studies of defects formation in crystals are of obvious importance in electronics, nuclear engineering and other disciplines where materials are exposed to different forms of irradiation. Rutherford Backscattering/Channeling (RBS/C) and Monte Carlo (MC) simulations are the most convenient tool for this purpose, as they allow one to determine several features of lattice defects: their type, concentration and damage accumulation kinetic. On the other hand various irradiation conditions can be efficiently modeled by ion irradiation method without leading to the radioactivity of the sample. Combination of ion irradiation with channeling experiment and MC simulations appears thus as a most versatile method in studies of radiation damage in materials. The paper presents the results on such a study performed on SrTiO3 (STO) single crystals irradiated with 320 keV Ar ions. The samples were analyzed also by using HRTEM as a complementary method which enables the measurement of geometrical parameters of crystal lattice deformation in the vicinity of dislocations. Once the parameters and their variations within the distance of several lattice constants from the dislocation core are known, they may be used in MC simulations for the quantitative determination of dislocation depth distribution profiles. The final outcome of the deconvolution procedure are cross-sections values calculated for two types of defects observed (RDA and dislocations).

We report here Swift heavy ion induced effects in GaN samples grown by metal organic chemical vapor deposition (MOCVD) technique. These samples were irradiated with 80 MeV Ni and 100 MeV Ag ions at a fixed fluence of 1 × 10 13 ions/cm 2 . Ion species and energies are chosen such that the difference in their electronic energy loss ( S e ) would be 8 keV/nm. Effects of Ag on structural and optical properties over Ni ions have been discussed extensively. We employed different characterization techniques like High Resolution X-ray Diffraction (HRXRD) and Raman Spectroscopy for defect density calculations and for vibrational modes, respectively. Defect densities are calculated and compared using Williamson–Hall method from HRXRD. Change of strain and vibrational modes with S e has been discussed.

III-Nitrides have attracted much attention due to their versatile and wide range of applications, such as blue/UV light emitting diodes. Strained layer super lattices offer extra degree of freedom to alter the band gap of lattice-mismatched hetero-structures. Swift Heavy Ion (SHI) irradiation is a post growth technique to alter the band gap of semiconductors, spatially. In the present study, strained AlGaN/GaN Multi Quantum wells (MQWs) were grown on sapphire with insertion of AlN and GaN as buffer layers between substrate and epi-layers by MOCVD. These buffer layers are known to improve the structural and optical properties. Such grown AlGaN/GaN MQWs were irradiated with 200 MeV Au ions at a fluence of 5 × 10 11 ions/cm 2 . As grown and irradiated samples have been characterized by HRXRD and PL. The analysis of symmetrical and asymmetrical reciprocal space mapping gives information on perpendicular and in-plane strain. Measured values show that lattice mismatch increases upon irradiation. However, increase in the mismatch upon irradiation has affected the band gap of MQWs, which has been confirmed by PL measurements. PL shows that there is an increase of intensity of luminescence of GaN and MQWs by one order of magnitude upon irradiation, which is attributed to SHI induced dynamic annealing processes.

III-Nitrides have attracted much attention due to their versatile and wide range of applications, such as blue/UV light emitting diodes. Strained layer super lattices offer extra degree of freedom to alter the band gap of lattice-mismatched heterostructures. Swift heavy ion irradiation is a post-growth technique to alter the band gap of semiconductors, spatially. In the present study, strained AlGaN/GaN multi-quantum wells (MQWs) were grown on sapphire with insertion of AlN and GaN as buffer layers between substrate and epilayers. Such grown AlGaN/GaN MQWs, AlGaN/GaN heterostructures and GaN layers were irradiated with 200 MeV Au and 150 MeV Ag ions at a fluence of 5 × 1011 ions/cm2 and 5 × 1012 ions/cm2 respectively. As-grown and irradiated samples have been characterized by high resolution XRD, photoluminescence and RBS/channelling. Measured strain values show that strain increases upon irradiation and the luminescence properties are enhanced. RBS/channelling confirms the increase in strain values upon irradiation. In this paper we describe the effects of swift heavy ion irradiation on structural and optical properties.

Ion-beam modification of material properties is of great interest from a research and industrial application point of view. In particular, modifications and characterizations of semiconductor heterostructures of nanoscale thickness have been investigated in great detail due to their potential applications in electronic and optoelectronic device applications. In this article, we review recent work in this field and present some of our results on irradiation studies of partially relaxed InGaAs/GaAs heterostructures, both thickness and composition dependence. Some of the recent results on GaN/Sapphire samples have also been discussed. We characterized these structures using high-resolution X-ray diffraction (XRD), Raman spectroscopy and RBS/Channelling. The defects densities have been obtained from high-resolution XRD and RBS/Channelling studies which are complemented by Raman results. The in-plane strain measured from XRD has been utilized to obtain the defects densities, which are confirmed by energy depen...

Epitaxial GaN layers grown by MOCVD on c -plane sapphire substrates are irradiated with 150 MeV Ag ions at a fluence of 5 × 10 12 ions/cm 2 . Samples used in this study are 2 μm thick GaN layers, with and without a thin AlN cap-layer. Surface morphology is studied using contact mode atomic force microscopy (AFM). Irradiated samples show qualitatively different morphologies as well as quantitative changes. Different kinds of morphology are attributed to specific type of dislocations using the existing models available in the literature. The residual strain and sample quality have been analysed before and after irradiation using high resolution X-ray diffraction (HRXRD). The Lorentzian shape analyses of the experimental scans complement the AFM results. Optical properties are studied by spectrophotometer used in the transmission mode. A sharp band-edge in the as grown samples was observed at ∼3.4 eV. The band-edge absorption broadened due to irradiation and these results have been discussed in view of the damage created by the incident ions which compliment HRXRD results. In general the effect of irradiation induced-damages are analysed as a function of material properties. A possible mechanism responsible for the observations has been discussed.

Strain relaxation and swift heavy ion irradiation effects on molecular beam epitaxy grown InGaAs/GaAs heterostructures have been studied by high-resolution X-ray diffraction. Symmetric and asymmetric scans were analyzed to understand the irradiation effects on strain and defects. The broad layer peak of the experimental scans in the samples was observed. The excess width of the layer peak than the expected one has been attributed to the strain relaxation induced defects. Irradiated samples show an additional peak close to the substrate peak of compressive nature, which has been attributed to radiation damage in the substrate due to the heavy ions. Dynamical scattering theory based simulations have been compared with the experimental scans. It has also been used to deconvolute the additional peak. The simulation was comparable with the experimental scan and a satisfactory fit was obtained. The dislocation density has been reduced upon irradiation. The observed decrease in the defect density is attributed to the high electronic energy loss of the ions near the interface region. Also, the damage created by the heavy ions near the interface would enhance the diffusion of indium across the interface and hence reduce the relative mismatch at the interface.

Analysis of defects by Channeling in strain relaxed In 0.18 Ga 0.82 As/GaAs heterostructures before and after swift heavy ion irradiation has been reported. Energy dependence of dechanneling parameter has been analyzed which indicates a thickness dependence of defects, involving dislocations (for 36 and 96 nm) and stacking faults (for 60 nm). The dislocation density reduces upon irradiation and the possibilities for the same have been discussed in detail. The cross-sectional transmission electron microscopy (TEM) analysis indicates the presence of stacking faults in 60 nm and dislocations in 96 nm irradiated samples complementing the dechanneling studies. Angular scans along off-normal axis have been carried out for strain analysis. A strong strain relaxation as a function of thickness is observed from the strain measurements. The strain values are almost same after irradiation compared with unirradiated ones. The flux distribution of channeled ions at smaller thicknesses is discussed in detail.

In0.18Ga0.82As/GaAs heterostructures of various layer thicknesses grown by molecular beam epitaxy (MBE) were irradiated by silver ions with a fixed energy and fluence. The thicknesses of the layers were beyond critical thickness and expected to be partially strain relaxed. The defects generated by partial strain relaxation and the effects of irradiation on these defects have been characterized by RBS/channeling. The dechanneling parameter and its dependence on incident ion energy has been determined. The resulting E0.5 dependence of the dechanneling parameter has been attributed to the presence of misfit dislocations at the interface. The effect of swift heavy ion (SHI) irradiation on partial relaxations is discussed in detail.

Ion beam induced modification and subsequent characterization of GaAs based hetero-structures (InGaAs/GaAs) have been investigated using ion channeling. The effect of Swift Heavy Ions (SHIs) on the elastic properties of these structures with varying layer thickness and incident ion fluence are discussed. A brief comparison with the results of high resolution XRD is presented. The angular scans of the irradiated samples are found to be broadened compared to the unirradiated samples, suggesting structural changes in the epilayer caused by SHIs. This broadening in thick film is more compared with the thin film. Although these scans are considerably broad, reasonably good minima indicate that the lattice crystallinity is intact.

A systematic study on structural defect buildup in 320 keV Ar-ion bombarded GaN epitaxial layers has been reported, by varying ion fluences ranged from 5x1012 to 1x1017 at/cm2. 1μm thick GaN epitaxial layers were grown on sapphire substrates using the MOVPE technique. RBS\channeling with 1.7 MeV 4He beam was applied for analysis. As a complementary method High Resolution Transmission Electron Microscopy (HRTEM) has been used. The later has revealed the presence of extended defects like dislocations, faulted loops and stacking faults. New version of the Monte Carlo simulation code McChasy has been developed that makes it possible to analyze such defects on the basis of the Bent Channel (BC) model. Damage accumulation curves for two distinct types of defects, i.e. Randomly Displaced Atoms (RDA) and extended defects (i.e BC) have been determined. They were evaluated in the frame of the MultiStep Damage Accumulation (MSDA) model, allowing numerical parameterization of defect transformations occurring upon ion bombardment. Displaced atoms buildup is a three step process for GaN and whereas extended defect buildup is always a two step process.

Ge nanocrystals embedded in SiO2 matrix have been synthesized by swift heavy ion irradiation of Ge implanted SiO2 films. In the present study, 400 keV Ge+ ions were implanted into SiO2 films at dose of 3 × 1016 ions/cm2 at room temperature. The as-implanted samples were irradiated with 150 MeV Ag12+ ions with various fluences. Similarly 400 keV Ge+ ions implanted into Silicon substrate at higher fluence at 573 K have been irradiated with 100 MeV Au8+ ions at room temperature (RT). These samples were subsequently characterized by XRD and Raman to understand the re-crystallization behavior. The XRD results confirm the presence of Ge crystallites in the irradiated samples. Rutherford backscattering spectrometry (RBS) was used to quantify the concentration of Ge in the SiO2 matrix. Variation in the nanocrystal size as a function of ion fluence is presented. The basic mechanism of ion beam induced re-crystallization has been discussed.

We report here swift heavy ion (SHI) irradiation induced effects on structural and surface properties of III-nitrides. Tensile strained Al(1-x)InxN/GaN Hetero-Structures (HS) were realized using Metal Organic Chemical Vapour Despotion (MOCVD) technique with indium composition as 12%. Ion species and energies are chosen such that electronic energy deposition rates differ significantly in Al(1-x)InxN and are essential for understanding the ion beam interactions at the interfaces. Thus the samples were irradiated with 80 MeV Ni6+ and 100 MeV Ag7+ ions at varied fluence (1×1012 and 3 ×1012 ions/cm2) to alter the structural properties. Under this energy regime, the structural changes in Al(1-x)InxN would occur due to the intense ultrafast excitations of electrons along the ion path. We employed different characterization techniques like High Resolution X- ray Diffraction (HRXRD) and Rutherford back scattering spectrometry (RBS) for composition, thickness and strain. HRXRD and RBS experimental spectra have been fitted with Philip’s epitaxy SIMNRA code, which yields thickness and composition from compound semiconductors. The surface morphology of pristine and irradiated samples is studied and compared by Atomic Force Microscopy (AFM).

Epitaxial AlGaN/GaN layers grown by molecular beam epitaxy (MBE) on SiC substrates were irradiated with 150 MeV Ag ions at a fluence of 5×1012 ions/cm2. The samples used in this study are 50 nm Al0.2Ga0.8N/1 nm AlN/1 μ m GaN/0.1 μ m AlN grown on SI 4H-SiC. Rutherford backscattering spectrometry/channeling strain measurements were carried out on off-normal axis of irradiated and unirradiated samples. In an as-grown sample, AlGaN layer is partially relaxed with a small tensile strain. After irradiation, this strain increases by 0.22% in AlGaN layer. Incident ion energy dependence of dechanneling parameter shows E 1/2 dependence, which corresponds to the dislocations. Defect densities were calculated from the E 1/2 graph. As a result of irradiation, the defect density increased on both GaN and AlGaN layers. The effect of irradiation induced-damages are analyzed as a function of material properties. Observed results from different characterization techniques such as RBS/channeling, high-resolution XRD and AFM...

Epitaxial AlGaN/GaN layers grown by MBE on SiC substrates were irradiated with 150 MeV Ag ions at a fluence of 5×1012 ions/cm2. AlGaN/GaN MQWs were grown on Sapphire substrate by MOCVD and irradiated with 200 MeV Au8+ ions at a fluence of 5×1011 ions/cm2 . These samples were used to study the effects of SHI on optical properties of AlGaN/GaN based nano structures. RBS/Channelling strain measurements were carried out at off normal axis of irradiated and unirradiated samples. In as grown samples, AlGaN layer is partially relaxed with a small compressive strain. After irradiation this compressive strain increases by 0.22% in AlGaN layer. Incident ion energy dependence of dechannelling parameter shows E1/2 dependence, which corresponds to the dislocations. Defect densities were calculated from the E1/2 graph. As a result of irradiation defect density increased on both GaN and AlGaN layer. Optical properties of AlGaN/GaN MQWs before and after irradiation have been analyzed using PL. This study shows that SHI increase the confinement effects in the MQWs and intensity of the active layer of the MQWs luminescence is increased by one order. This may be due to the induced strain in GaN and AlGaN layers. Some unwanted yellow luminescence has also been introduced by the SHI possibly due the point defects or defect luminescence from the induced dislocations in GaN bulk epitaxial layers. In this study, we present some new results concerning high energy irradiation on AlGaN/GaN heterostructures and MQWs characterized by RBS/Channelling and PL.

Epitaxial GaN layers grown by MOCVD on c‐plane sapphire substrates were irradiated with 150 MeV Ag ions at a fluence of 5×1012 ions/cm2. Samples used in this study are 2 μm thick GaN layers, with and without a thin AlN cap‐layer. Energy dependent RBS/Channeling measurements have been carried out on both irradiated and unirradiated samples for defects characterization. Observed results are compared and correlated with previous HRXRD, AFM and optical studies. The χmin values for unirradiated samples show very high value and the calculated defect densities are of the order of 1010 cm−2 as expected in these samples. Effects of irradiation on these samples are different as initial samples had different defect densities. Epitaxial reconstruction of GaN buffer layer has been attributed to the observed changes, which are generally grown to reduce the strain between GaN and Sapphire

The effect of swift heavy ion (SHI) irradiation on InGaAs/GaAs heterostructures is studied using Raman spectroscopy and atomic force microscopy (AFM). The structures consist of molecular beam epitaxy (MBE) grown InGaAs layers on GaAs(001), having layer thicknesses of 12, 36, 60 and 96 nm. After irradiation, the GaAs type longitudinal optical (LO) mode blue shifted to higher frequency in thin samples and red shifted towards lower frequency in thick samples. These results are discussed invoking the penetration depth of the probe radiation (lambda = 514.5 nm) in InGaAs. Deconvoluting the Raman spectra of thin samples indicates a compressive strain developed in the substrate, close to the interface upon irradiation. This modification and diffusion of indium across the interface results in an increase of strain and reduction of the defect densities in the InGaAs layer. The variations in FWHM of the Raman modes are discussed in detail. The surface morphology of these heterostructures has been studied by AFM before and after SHI irradiation. These studies, combined with Raman results, help to identify different relaxation regimes. J Phys Condens Matter

The importance and advantages of heterostructures and Quantum Wells (QWs) in device technology has made research challenging due to lack of direct techniques for their characterization. Particularly the characterization of strain and defects at the interfaces has become important due to their dominance in the electrical and optical properties of materials and devices. RBSiC has been used to study variety of defects in single crystalline materials, for nearly four decades now. Channeling based experiments play a crucial role in giving depth information of strain and defects. Ion beams are used for both material characterizations as well as for modifications. Hence it is also possible to monitor the modifications online, which are discussed in detail. In the present work, Swift Heavy Ion (SHI) modification of III-V semiconductor heterostnictures and MQWs and the results of subsequent strain measurements by RBSiC in initially strained as well as lattice matched systems are discussed. We find that the compressive strain decreases due to SHI irradiation and a tensile strain is induced in an initially lattice matched system. The incident ion fluence dependence of strain modifications in the heterostructures will also be discussed. The use of high energy channeling for better sensitivity of strain measurements in low mismatch materials will be discussed in detail. Wherever possible, a comparison of results with those obtained by other techniques like HRXRD is given.