Range Of Dislocation Densities Research Articles

Comparative study of methods for counting of dislocations in 4H-SiC

Three experimental techniques to determine the density of the three relevant dislocation types (basal plane, threading edge and threading screw) in SiC were investigated: etching by molten KOH with and without the addition of Na2O2 and X-ray topography. The applicability to implement these techniques for a reliable full-wafer scale analysis is tested experimentally. The limitations are found to be mainly determined by the feature sizes. Based on simple considerations, the range of acceptable sizes of the dislocation-related features is estimated. Etching with Na2O2 allows to distinguish between all three types of dislocations, but a reliable detection is difficult to set up due to a too large spread of etch pit size. Without the addition of Na2O2, TSD and TED cannot be distinguished, but etch pit sizes become more homogeneous, enabling robust etch pit detection over a wider range of dislocation densities. X-ray topography gives reliable results for TSDs and BPDs whereas the measurement of TEDs is limited.

Device performance of chemical vapor deposition monocrystal diamond radiation detectors correlated with the bulk diamond properties

Diamond radiation detectors (DRDs) based on type-IIa chemical vapor deposition (CVD) monocrystal diamond are more suitable for engineering applications with high consistency requirements due to the lower cost and property controllability. However, their saturated charge collection efficiencies (CCEs) have huge differences. Six type-IIa CVD monocrystal diamond plates were analyzed by the Fourier transform infrared spectrometer, high resolution x-ray diffraction, Raman spectroscopy, photoluminescence and secondary ion mass spectroscopy. Then DRDs were fabricated by them and the CCEs were measured under the irradiation of 241Am source. The results show that the most important factor restricting CCEs are the impurities in the diamond plates, while dislocations with a density <1 × 107 cm−2 for all samples have weaker impact in our case. The reason is that the carrier mobility-lifetime (μτ) product of diamond is more strongly influenced by impurities in this dislocation density range. Thinning diamond plate, if the thickness is kept above 100 μm, is not a good means to obtain high performance DRDs. Therefore, to further improve the detector performance, ultra-high purity diamond growth is most important. Moreover, a diamond test and selection scheme for high performance DRDs is also demonstrated.

Effect of Character and Dispersion of Dislocations on the Strengthening Behavior of Cold Worked Ferritic Steel

Dislocation strengthening is affected by not only dislocation density but also character and dispersion of dislocations. In terms of the effect of dislocation dispersion, strengthening behavior can be explained by applying a dispersion coefficient; δ (= n / ρ) in theoretical dislocation strengthening equation, here n and ρ are the number of dislocation colonies on a slip plane and dislocation density respectively. Dislocation pinning spacing is given as a function of n –value, so that the increment of strength Δσ can be theoretically estimated using the dispersion coefficient δ. In cold rolled ferritic steel (Fe-0.0056%C), the comparison of theoretical values with experimental data proved δ≒0.21 in the dislocation density range above 1×1014/m2. In addition, experimental results indicated that the screw component of dislocations decreases with an increase of dislocation density. With respect to the ability of dislocation strengthening, edge dislocation is about 1.4 times larger than screw dislocation. As a result, a linear Bailey-Hirsch relationship; Δσ[GPa]≒1.8×10−8ρ is realized due to the changes of dislocation character with an increase of dislocation density.

Mesoscale Modeling of High Burn-Up Structure Formation and Evolution in UO2

A phase-field model was developed to simulate the high burn-up structure formation and evolution in UO2. The model takes into account the interfacial energies of grain boundaries and bubble surfaces, the strain energy associated with dislocations, and the chemical energy of gas atoms. This enables the model to simulate the formation and growth of sub-grains and bubbles in a self-consistent manner. The model results demonstrate strong effects of dislocation density (its magnitude and distribution), grain boundary energy, and bubble radius and number density on the formation of the sub-grains. For polycrystalline UO2, the model predicts the average size of the recrystallized grains to lie within the range of 0.3–0.5 µm corresponding to a dislocation density range of $$ \rho = (2.5 \times 10^{15} - 2.65 \times 10^{15} ) \;{\text{m}}^{ - 2} $$ or equivalent to 70–75 GWd/tHM burn-up. These predictions agree reasonably well with data reported in the literature.

Vertical Current Transport in AlGaN/GaN HEMTs on Silicon: Experimental Investigation and Analytical Model

We investigate the vertical leakage mechanism in metal–organic chemical vapor deposition-grown carbon (C)-doped AlGaN/GaN High Electron Mobility Transistors (HEMTs) on 6-in silicon wafer. Substrate bias polarity-dependent ${I}$ – ${V}_{s}$ , temperature-dependent fitting, and band diagram analysis pointed to the Poole–Frenkel (P–F) type of conduction mechanism for vertical transport in the devices with breakdown as high as 580 V for a buffer of $\textsf {4}~\mu \text{m}$ . Trap activation energy of 0.61 eV was estimated from the P–F fitting which matches well with values reported in the literature. We propose that higher dislocation density leads to shallower traps in the buffer and build an analytical model of dislocation-mediated vertical leakage around this. The variation in leakage as a function of dislocation density at a given field is predicted and is found to be the most abrupt in the range from $\sim 10^{\textsf {7}}$ to $\sim 10^{\textsf {9}}$ cm $^{-\textsf {2}}$ of dislocation density. This can be attributed to a sharp decrease in trap activation energy in the above range of dislocation density, possibly due to complex formation between point defects and dislocations.

Efficiency of dislocations as sinks of radiation defects in fcc copper crystal

The sink efficiency of perfect dislocations for self-point defects (interstitials and vacancies) in fcc copper crystal has been calculated by the kinetic Monte Carlo method in a temperature range of 293–1000 K and a range of dislocation densities from 1.3 × 1012 to 3.0 × 1014 m−2. Screw, mixed, and edge dislocations with a Burgers vector 1/2 in different slip systems are analyzed. The interaction energies of self-point defects with dislocations are calculated using the anisotropic theory of elasticity. Analytical expressions are proposed for the dependences of the calculated values of dislocation sink efficiency on temperature and dislocation density.

Interplay of stimulated emission and Auger‐like effect in violet and blue InGaN laser diodes

AbstractWe have studied two types of InGaN laser diodes emitting at 410 and 440 nm, looking for the presence of the efficiency “droop” and its influence on the performance of these devices. By measuring the devices in two experimental geometries: a) along the resonator axis, b) perpendicularly to the cavity, we were able to conclude that the light emission process in these laser diodes operating below the threshold are governed by two mechanisms: Auger‐like effect and the stimulated recombination. The competition of these two mechanisms leads to the suppression of the droop if the light is observed along the axis of the cavity. The relatively low onset of the stimulated recombination may account for the robustness of these devices against the nonradiative process (Auger‐like recombination) appearing at high current densities. Additionally, we performed the characterization of InGaN light emitting diodes grown on substrates with varied In content and defect density. The results clearly demonstrate that the droop is not related in any way with the above mentioned parameters at least in the dislocation density range between 105 and 109 cm‐2 and In composition range between 0.1‐0.15. (© 2010 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

X-ray characterisation of zinc oxide (ZnO) single crystal substrates

Single crystal substrates of low defect density are paramount for fully realising the numerous applications of zinc oxide (ZnO) wide bandgap semiconductors. While ZnO substrates are commercially available from various vendors, very little information is available on the structural properties of these substrates. Therefore, an extensive evaluation of available substrates would serve as a basis for the development of ZnO based devices and technologies. In this study, bulk ZnO single crystal substrates grown by different growth techniques have been characterised using synchrotron white beam X-ray topography and high resolution X-ray diffraction. The substrates exhibit a wide range of dislocation densities from as high as 106 cm–2 down to less than 1000 cm–2 depending on the growth technique employed. The authors' evaluation reveals that ZnO crystals grown by the hydrothermal technique possess the best structural quality with dislocation densities of 800–1000 cm–2 and rocking curves with a full width half maximum of less than 12 arc seconds.

Effects of hydrogen on majority carrier transport and minority carrier lifetimes in long-wavelength infrared HgCdTe on Si

We present extended results on the use of a hydrogen plasma to passivate the effects of defects in long-wave ir HgCdTe/Si. Annealed and as-grown epilayers, in situ doped with indium, were exposed to a hydrogen plasma generated in an electron cyclotron resonance (ECR) reactor. Secondary ion mass spectrometry was used to measure the extent of hydrogen incorporation into the epilayers. Hall and photoconductive lifetime measurements were used to assess the efficacy of passivation. The passivation of defects responsible for the scattering and recombination of electrical carriers was observed for most ECR conditions over a range of dislocation densities.

In-plane imperfections in GaN studied by x-ray diffraction

We have studied a series of GaN films grown with a range of dislocation densities by atomic force microscopy (AFM), transmission electron microscopy (TEM) and high resolution x-ray diffraction (HRXRD). The (002), (004), (006), (105), (204), (302), (100), (110), (200) and (300) reflections were measured as reciprocal space maps (RSMs) or scans in ω and ω/2θ. The latter 4 in-plane reflections were measured using a low, or glancing, incident angle with respect to the film surface. We have used a variety of different methods to try and obtain reliable measurements for mosaic tilt, twist, crystallite size and microstrain both in- and out-of plane. From (hk0) data in-plane twist angles were measured ranging from 0.37° to 0.078° and in-plane microstrains from 3.5 × 10−4 to 1.8 × 10−4. The improvements in the quality of the GaN layers relate to the increased island coalescence time, which reduces in particular the number of edge-type threading dislocations. The first three samples had a much larger tilt ∼0.09° than the last three ∼0.04°. However, the latter samples were bowed, so results from a single measurement on the (002) peak are too large. Beam restriction on the (002) or an extrapolation from several (00l) reflections gives more reliable results. The values obtained for in-plane crystallite size are in general variable or unreliable. For some samples the sizes are considered to be too large to be accessible by XRD; in most cases the peak broadening is dominated by tilt or twist or microstrain and the results are sensitive to assumptions about the peak shape. For the samples with smaller measurable crystallite sizes, the (hk0) peaks were too weak to measure reliably. The cell parameters showed more compressive strain with fewer dislocations. The trends observed by HRXRD are consistent with AFM and TEM results.

Effects of dislocations on the luminescence of GaN/InGaN multi-quantum-well light-emitting-diode layers

Photoluminescence (PL) and cathodoluminescence (CL) of light emitting diode samples with various InGaN/GaN multi-quantum-well (MQW) active structures and a range of dislocation density (∼7×10 8/cm 2 to ∼9×10 9/cm 2) were investigated. Results indicate that threading dislocations have impact on the luminescence of GaN thin films and act as a nonradiative recombination center. It was also observed that the optical emission is affected by MQW structure such as the number of quantum wells.

Near-band gap luminescence at room temperature from dislocations in silicon

Cathodoluminescence (CL) has been used to investigate room-temperature light emission from dislocations generated by ion-implantation. Czochralski silicon wafers were implanted with boron and silicon ions at a range of doses and energies to produce, after suitable thermal annealing, a band of dislocation loops typically ∼150nm from the surface. Room-temperature CL from specimens with a range of dislocation densities was observed with a peak wavelength of 1154nm. The luminescence was found to be independent of the presence of a p–n junction and the luminescence efficiency was lower for the relatively lowly doped silicon implanted samples than in the case of the highly doped boron implanted samples. We attribute the luminescence behaviour to electron–hole recombination at the dislocations themselves and propose a model for this near-band gap luminescence based on one-dimensional energy bands previously associated with the strain field of dislocations.

Effect of dislocations on performance of LWIR HgCdTe photodiodes

The epitaxial growth of HgCdTe on alternative substrates has emerged as an enabling technology for the fabrication of large-area infrared (IR) focal plane arrays (FPAs). One key technical issue is high dislocation densities in HgCdTe epilayers grown on alternative substrates. This is particularly important with regards to the growth of HgCdTe on heteroepitaxial Si-based substrates, which have a higher dislocation density than the bulk CdZnTe substrates typically used for epitaxial HgCdTe material growth. In the paper a simple model of dislocations as cylindrical regions confined by surfaces with definite surface recombination is proposed. Both radius of dislocations and its surface recombination velocity are determined by comparison of theoretical predictions with carrier lifetime experimental data described by other authors. It is observed that the carrier lifetime depends strongly on recombination velocity; whereas the dependence of the carrier lifetime on dislocation core radius is weaker. The minority carrier lifetime is approximately inversely proportional to the dislocation density for densities higher than 105 cm−2. Below this value, the minority carrier lifetime does not change with dislocation density. The influence of dislocation density on the R0A product of long wavelength infrared (LWIR) HgCdTe photodiodes is also discussed. It is also shown that parameters of dislocations have a strong effect on the R0A product at temperature around 77 K in the range of dislocation density above 106 cm−2. The quantum efficiency is not a strong function of dislocation density.

X-ray diffraction peaks due to misfit dislocations in heteroepitaxial structures

The x-ray scattering from relaxed heteroepitaxial layers with the misfit dislocations randomly distributed at the interface between the layer and the substrate is analyzed theoretically and experimentally. The profiles of the x-ray-diffraction peaks and the reciprocal space maps of the intensity are measured and simulated for several heteroepitaxial structures in a wide range of dislocation densities. At large dislocation densities, the peak position is governed by the mean distortions and the peak width is due to the mean-square variations of the distortions. The peak widths calculated for uncorrelated distribution of dislocations exceed the widths of the peaks measured on the heteroepitaxial structures with large mismatch. It is shown that the spatial correlations of the dislocations reduce the peak width and explain the discrepancy. For small dislocation densities, the coherent and the diffuse components of the intensity are measured and simulated. It is shown that the position of the coherent peak does not follow the mean distortions. Satellites of the diffuse peak are observed and explained.

Contrasting the 0.3 μm depth carrier concentration with dislocation density in a Si-implanted layer

The dislocation distribution effect on the carrier concentration distribution at a depth of 0.3 μm in a Si-implanted layer has been investigated by means of the Lang X-ray topograph technique and by means of the capacitance-voltage ( C- V) method using a 200 μm diameter Schottky diode array. In the range of dislocation density < 10 6–10 7 cm −2, there is no direct relationship between the 0.3 μm depth carrier concentration and dislocation density in a semi-insulating GaAs substrate obtained from a liquid-encapsulated Czochralski-grown crystal boule.

The dislocation bias during irradiation: Effects of climb motion and rate limitation

Abstract The elastic-field model of a dislocation embedded in a lossy continuum is used to derive, analytically and rigorously, self-consistent expressions for the dislocation sink strength suitable for use in the chemical rate theory approach to the study of microstructural evolution during irradiation. These new expressions take proper account of the synergistic effects of the long-range elastic interaction between dislocations and point defects, dislocation climb motion, core rate limitation, and the influence of all types of sink involved. Numerical results are given for a range of dislocation densities, neutral sink strengths, temperatures, point-defect production rates and transfer lengths. It is found that making allowance for climb motion leaves the dislocation bias factor for interstitials essentially unchanged but increases that for vacancies, thus bringing a reduction of the dislocation net bias about. Making allowance for rate limitation, on the other hand, leads to a decrease of the dislocati...

ＫＣｌ単結晶の鋼球および四角すい圧子押し込みによる変形

In order to elucidate the mechnism of friction and wear, it is necessary to have a knowledge on deformation in materials produced by invasion of sharp projections or wear particles.In this study, the cleaved faces of KCl single crystal were indented with a steel ball or a Vickers diamond indentor. The deformation and hardness around the indentation were examined from macroscopic viewpoints, and the dislocation patterns were observed from microscopic one. The results obtained are as follows:(1) The indents formed on the indented surfaces with a ball or a pyramid were not perfectly circular nor square in shape due to the crystal anisotropy.(2) The appearances of the pile-up and sink-in around indents were clarified.(3) The strain hardening around the indent was more active in the ‹110› direction than in the ‹100›.(4) The deformed area on {100} face with a ball or pyramidal indentor consisted of a high dislocation density range and a wing shaped area of comparatively low density extended along the ‹110› and ‹100› directions.(5) The hardness and the dislocation density were related each other.(6) The etch pit patterns in the cleaved cross section were observed on {110}45 faces.

Analysis of InGaAs/InP multi-quantum-well structures by ion backscattering : H. Leier, F. Burgazy, A. Forchel, K. Streubel, F. Scholz and M. Pilkuhn. Vacuum39(2–4), 79 (1989)

Photoluminescence (PL) and cathodoluminescence (CL) of light emitting diode samples with various InGaN/GaN multi-quantum-well (MQW) active structures and a range of dislocation density (∼7×108/cm2 to ∼9×109/cm2) were investigated. Results indicate that threading dislocations have impact on the luminescence of GaN thin films and act as a nonradiative recombination center. It was also observed that the optical emission is affected by MQW structure such as the number of quantum wells.

The effect of climb motion on the dislocation bias during irradiation

Abstract The elastic-field model of a dislocation embedded in a lossy continuum is used to derive, for the first time, self-consistent expressions for the dislocation sink strength suitable for use in the chemical rate theory approach to the study of micro structural evolution during irradiation, when the sensitivity of physical observables (such as void swelling or the dislocation climb rate itself) to the diffusion-controlled dislocation climb motion is required. It is shown that making allowance for climb motion leads to an increase in the dislocation bias factor for vacancies compared with that for interstitials, and to a concomitant reduction of the dislocation net bias and the actual dislocation climb rate. Numerical results are given for a wide range of dislocation densities, neutral sink strengths, temperatures and point-defect production rates, and particular attention is drawn to the significance of climb motion for charged-particle simulation conditions.

Minority carrier lifetime in the region close to the interface between the anodic oxide and CdHgTe

This paper describes minority carrier lifetime in n-type CdHgTe surface layers, especially the relationship between minority carrier lifetime and dislocations. A new method has been developed to evaluate lifetime in the surface layer of semiconductors. This method measures the concentration of minority carriers remaining after injection by utilizing surface potential measurement of an MIS diode. Computer simulation reveals how dislocations affect minority carrier lifetime and confirms the validity of this method. Experimental results indicate the dislocation-induced recombination is dominant for dislocation densities over 5×10 5 cm -2 and that minority carrier lifetime is inversely proportional to dislocation density. These results are similar to the results of the R 0 A product as a function of dislocation densities that have been reported by Colombo and Syllaios. The conjugate pairs r (radius of dislocation pipe) and s (recombination velocity at the dislocation site) are 0.3 to 0.5 cm 2 s -1. The lifetimes become almost constant - scatter 3 to 4 μs - for dislocation densities less than 2×10 5 cm -2. Lifetime is not dominated by dislocations in this dislocation density range.