Dislocation Pits Research Articles

Residual stress and subsurface damage in sapphire ultra-precision grinding

This study conducted experiments on ultra-precision grinding of sapphire using various strategies. It evaluated surface and subsurface characteristics across multiple dimensions, including morphology, scale, mechanical properties, residual stresses, lattice distortions, in-service properties, and chemical components. The research aimed to explore the intrinsic relationship between these behaviours. The findings revealed that both semi-finish grinding and ultra-precision grinding achieved ductile and low-roughness surfaces, with surface hardness enhancement near the grinding surface. Additionally, Raman spectra wave shifts were able to distinguish residual stresses at different grinding strategies, with larger stresses observed in ultra-precision grinding compared to semi-finish grinding and rough grinding. Furthermore, dense etching dislocation pits were observed on the ultra-precision grinding surface, responding to the scale of residual stress. The presence of larger subsurface cracks in semi-finish grinding and rough grinding was found to contribute to the release of residual stress. Moreover, ultra-precision grinding significantly reduced subsurface damage compared to rough grinding, with a reduction from 23.8 μm to 4.3 μm. Photothermal absorption during rough grinding was noted to be over 10 times higher than in ultra-precision grinding. Transmission electron microscopy (TEM) analysis revealed that subsurface damage included microcrack-induced line defects and uniform plastic deformation areas. This damage involved lattice aberrations, dislocations, stacking faults, and thin amorphous layers. The hardness and modulus of the subsurface damage layer were observed to decrease. Additionally, Raman spectra wave shifts were able to distinguish the subsurface damage layer in ultra-precision grinding. Energy-dispersive X-ray spectroscopy (EDS) analysis showed no change in the chemical components of the subsurface damage layer. Furthermore, a model was proposed to evaluate subsurface damage based on residual stress, and the mechanism of residual stress inducing damage in ultra-precision grinding was further analysed.

Dislocations in monoclinic cadmium tungstate CdWO4

Several types of dislocations were found in CdWO4 single crystals. In-grown dislocations slip on (100) plane parallel to [001]. Dislocation pits were revealed in mechanically polished samples on (100) and (010) planes. Based on the results of chemical etching, it was inferred that the lattice dislocations gliding along < 001 > and < 100 > can split into partial dislocations. In the samples annealed at T = 600ºC for 2 h dislocation density decreased noticeably. After annealing shape and sizes of helical etch pits on (100) and (001) planes transform to those typical of lattice dislocations.

Mechanistic insights into the formation of dislocation-related pits on diamond surface under plasma etching treatment: A combined simulation and experimental approach

Reactive ion etching (RIE) is a widely applied technique for high-precision machining of demanding diamond devices. However, the persistent challenge of widely distributed dislocation-related etch pits on processed surfaces remains poorly understood. In this study, the material removal and pit formation during the etching of the dislocation region by hydrogen and oxygen were investigated by reactive force-field (ReaxFF) molecular dynamics simulation combined with experimental verification. The results unveiled the pivotal role of crystal structure disruption and symmetrically distributed stress, induced by dislocations, in promoting bond-breaking processes and triggering the formation of etch pits. The etching parameter optimized simulations revealed that once the impact effect of oxygen atoms counterbalances the promotion of dislocation to the bond breaking, the formation of dislocation pits can be effectively avoided, which is convincingly validated by experimental results. Besides, our research further verified that pure hydrogen etching is an inefficient surface post-treatment process with a more significant pit-forming problem, and exists two distinct pit-forming mechanisms dependent on the incident energy. Additionally, substrate temperature variation has global but negligible influences on pits formation within the 400 K range. These findings carry significant implications for the optimization of processing parameters and the large-scale implementation of RIE in diamond processing, demonstrating the potential to address pit-forming issues with commonly used gases.

Impact of nanosecond UV laser pulses on the surface of germanium single crystals

For the first time, a detailed comprehensive study of the "dry" etching of dislocation and dislocation-free germanium samples on the {111}, {110} and {100} planes has been carried out. Etching was carried out by exposure to pulses of nanosecond UV laser radiation of subthreshold intensity (wavelength 355 nm, duration ~ 10 ns, energy density ~ 0.5–1.3 J/cm2, pulse repetition rate 100 Hz, divergence 1–2 mrad). Before and after laser heat treatment of the surface, the samples were examined using a Zygo optical profilometer and a scanning electron microscope. Features of the nature of damage to surfaces corresponding to different crystallographic planes of single crystals of industrial dislocation germanium are revealed. They are compared with data on subthreshold damages of typical dislocation-free crystals.It is shown that in dislocation samples of germanium on the {111} plane, it is possible to create a regime of exposure to radiation, leading to the formation of etch pits that are outwardly identical to dislocation pits detected during selective chemical etching. Their concentration corresponds in order of magnitude to the density of dislocations.On the {100} plane of dislocation samples, etching results were also found, which clearly have a crystallographic nature. At an energy density of the acting radiation ≥ 0.4 J/cm2, on the surfaces of dislocation ({100} plane) and dislocation-free germanium ({111}, {100}, {110} planes), only individual spots ~ 50 μm in size were registered, as well as individual microcraters ~ 0.1–1 μm in size, which do not have crystallographic features. The possibility of environmentally friendly detection of dislocations in germanium without the use of chemical reagents is shown.

Electrostructural and morphological features of etch pits in boron-doped HPHT-diamond single crystals and multisectoral plates

Morphological, structural, and nano-electrical features of the growth defects and sectoral boundaries revealed by selective etching in synthetic boron-doped single crystals of diamond (BDD) and multisectoral plates are characterized by a set of scanning probe microscopy (SPM) methods, confocal micro-Raman, and micro-FTIR spectroscopy. Diamond single crystals were grown under high pressure and high temperature conditions (HPHT) in the FeAlBC system. Morphology of dislocation etch pits and micro-defect related pits/protrusions compared both on the growth facets and multisectoral plates cut parallel to the {110} facet of BDD single crystals. Ex situ AFM observation of the etched surface revealed non-homogeneously distributed pits and protrusions over the growth facets correlated with irregular macroscopic growth defects. There is a center-to-periphery gradient of dislocation density in multisectoral plates. The protrusions are homogeneously distributed over plates; some often decorate dislocation pits. Micro-Raman mapping on dislocation pits (boron-rich regions) decorated by low-boron content regions revealed crystalline imperfections in three dimensions, with apparent compressive/tensile strain. The defects were mainly electrically neutral under surface potential mapping by Kelvin probe force microscopy, opposite to the inter-sectoral boundaries having pronounced surface potential steps. The scanning spreading resistance microscopy shows resistivity variations at etching-reviled surface defects and sectoral boundaries if the appropriate DC bias is applied to the SPM tip.

Understanding the Crystalline Region Damage Mechanism of XLPE in Water Tree Propagation by Erosion Method

This study investigates the damage characteristics and mechanism of the crystalline regions of cross-linked polyethylene (XLPE) in water tree propagation. XLPE cable samples are subjected to an accelerated water tree aging at a voltage of 7.5 kV/400 Hz for 240, 480 and 720 hours. After the water tree aging, the crystalline structural changes of the water tree samples are observed by X-ray diffraction (XRD). In addition, the water tree samples are eroded and the morphologies of the crystalline regions in water tree regions are observed by a scanning electron microscope (SEM). The XRD results show that the crystallinities of the aged samples decrease with aging, especially after 240 hours. The SEM results show that after 240 hours of aging, slip lines and dislocation steps emerge on the fracture surfaces. After 480 hours, microcracks with sizes of several micrometers are observed in the directions of the crystal faces. After 720 hours, conical dislocation pits appear in the samples and there are microvoids at the bottoms of the pits. Based on the XRD and SEM results, it is concluded that the crystalline regions of XLPE are damaged in the water tree aging. At last, the initiation process of the dislocations and the damage characteristics of the crystalline regions in the water tree propagation are discussed.

Impact of dislocation pits on device performances and interface quality degradation for E-mode recessed-gate Al2O3/GaN MOSFETs

The degradation of device electrical characterizations and MOS interfacial quality caused by dislocation pits on recessed-gate GaN surface are directly observed and investigated for e-mode Al2O3/GaN MOSFETs on Si substrate. The pits have resulted in negative shift of threshold voltage (Vth), large gate leakage current and deteriorated channel conduction. Moreover, the serious gate trapping effects reflected in Vth instability are confirmed to be correlated with these pits. It has been mainly attributed to the formation of poor-quality MOS interface with high density of interface traps more than 1013 cm−2eV−1. Further experimental measurements reveal that the pits tend to induce detrimental Ga–O on the recessed GaN surface, generally known as a common origin of interface traps, and thus cause the undesirable effects. A lower pits density helps to suppress the Ga–O, and improve the interface stability and device performances of e-mode MOS-gate GaN transistors.

Informative Aspects of Molten KOH Etch Pits Formed at Basal Plane Dislocations on the Surface of 4H‐SiC

Despite being a destructive technique, molten KOH etch pits at basal plane dislocations are found to have informative aspects, as revealed by photoluminescence imaging and optical microscopy, on the 4° off‐cut (0001) surface of 4H‐SiC p–i–n diode chips, where single Shockley‐type stacking faults have expanded during electroluminescence experiments. Smaller etch pits are observed aligning on single lines along ±[100] that are the shallowest sides of stacking faults. Through closer observation of the pits, the facing directions are found to agree well with a model explaining the two types of partial dislocations constituting the line. Other basal plane dislocation pits are observed by scanning electron microscopy on the sublimation‐grown wafer surface before epitaxial growth. The distances between the partial dislocation cores are measured at each pit. No basal plane dislocation etch pit facing toward ±[100] is found, but a weak correlation is noted between the partial dislocation distance at the cores and the direction that the basal plane dislocations face. The corresponding results are discussed in terms of the image force and the force exerted on steps perpendicular to the (0001) plane, to understand the mechanisms of basal plane dislocation propagation and/or conversion to threading edge dislocations.

High-Speed MOVPE Growth of InGaP Solar Cells

Impacts of reactor pressure and growth temperature on the qualities and properties of InGaP epitaxial layers grown in a narrow-channel horizontal metalorganic vapor-phase epitaxy (MOVPE) reactor were investigated with a growth rate of 10 μm/h. The roughness of InGaP was improved remarkably when the pressure was increased from 6 to 10 and 15 kPa. The reason is most likely related to the absolute pressure of P and the migrations of In and Ga adatoms on the wafer surface. Owing to the gas-phase reactions and desorption of P from InGaP, the surface of InGaP became rough, and the pit dislocation was increased with an increase in growth temperature. Although a low temperature was beneficial in order to obtain a smooth InGaP surface, the carrier lifetime in InGaP was shortened as a drawback. Consequently, InGaP n-on-p solar cells grown at a low temperature suffered from the degradations of both short-circuit current density and open-circuit voltage. Background impurities and defect densities in low temperature grown InGaP were attributed to these deteriorations. At the optimized growth temperature of 650 °C and the reactor pressure of 15 kPa, the growth rate of InGaP was accelerated to 20 and 30 μm/h. InGaP solar cells were successfully fabricated with the rate of 30 μm/h that opened up the way for the fabrication of III–V multijunction solar cells in the high-speed MOVPE reactor.

Wet etching generation of dislocation pits with clear facets in LEC-InAs single crystals

Dislocation etch pits with clear rectangular and elongated hexagonal shapes on indium arsenide (1 0 0) wafer surface have been obtained by carefully controlling the etch condition of HCl-based etchant with the addition of a surfactant. Etching activation energies of (1 0 0), (1 1 1)A and (1 1 1)B faces have been obtained by etching at different temperatures. The results suggest a chemically-controlled reaction restricted by the surfactant. Indices of the facet surfaces in the pits were analyzed with the aid of optical microscopy as well as pit side wall cross section observation by cleavage. It is similar to the etch pit facets of an In-doped GaAs wafer. Mechanism of the etching behavior of InAs has been discussed based on the results.

Quantification of roughness and spatial distribution of dislocations in MBE and MOVPE grown LED heterostructures

A combination of nanoscale imaging techniques such as atomic force microscopy and scanning electron microscopy are used to investigate the relationship between surface morphology and height statistics of GaN cap layers in InGaN/GaN light emitting diode heterostructures. The investigated samples were grown in two very different growth regimes which lead to distinct characteristic superficial landscapes. We also report here on the introduction of a new methodological approach that adapt the concept of height-height correlation function, a well known statistical tool in the field of studies on rough surfaces. We evaluate to which extent the geometrical properties of the constitutive ‘bricks’ (hillocks for ammonia assisted molecular beam epitaxial film) and structural defects (dislocation pits for metal organic vapor phase epitaxial film) affects the statistical properties of heights of these GaN surfaces. Finally, we have studied the spatial distribution of dislocation pits in both the samples to assess the quantitative differences between these heterostructures of very distinct surface morphology.

Influence of Hydrogen Post-Implantation on Threading Dislocation Density in Strain-Relaxed Sige Layer

According to International Technology Roadmap for Semiconductor (ITRS), the development of MOSFETs based on SiGe or Ge is necessary for the next generation technology beyond 10-nm C-MOSFETs, because electron and hole mobility of Ge substrate is three and four times higher than those of a conventional Si MOSFETs, respectively. However, due to the lattice mismatch of 4.2 % between Si and Ge, many threading dislocations are generated, resulted in increasing the leakage current of the C-MOSFETs. The threading dislocation density of graded SiGe layer utilized currently is higher than 105 cm-2, which is too high to be applied in mass production because of degrading productivity and performance of the C-MOSFETs. To overcome this drawback in realizing sub 10-nm C-MOSFETs, a novel process technology should be developed to reduce the threading dislocation density. In this study, we designed a novel technology to reduce the threading dislocations in strain-relaxed Si1-xGex grown on Si substrate. We applied the H+ post-implantation which forms defect band at the dislocation clusters above the interface between the Si1-xGex layer and the Si substrate, acting as a dislocation sink. We investigated how the hydrogen-ion implantation followed by annealing affected the surface characteristics, such as dislocation pit and cross-hatch pattern density related the threading dislocation. In particular, the cross-hatch pattern density of the Si0.8Ge0.2 layer on the Si substrate was about 4x104 cm-1, as shown in Fig. 1(a). On the other hand, when hydrogen ions were implanted into the relaxed Si0.8Ge0.2 layer with an dose of 5x1015 cm-2, the cross-hatch pattern density was reduced to about 1.18x104 cm-1, as shown in Fig. 1(b). Also, there was a high threading dislocation density in the case of 30-at% Ge concentration, as shown in Fig. 2(a). However, for the case of hydrogen ion implantation, a dose of 5x1015 cm-2, both threading and misfit dislocations near the interface between Si0.7Ge0.3and Si substrate were significantly reduced, as shown in Fig. 2(b). Therefore, we present the mechanism of the strain relaxation resulted in the formation of the threading dislocation in Si1-xGex/Si (100) substrate. In addition, we explain how H+ implantation affects the cross-hatch pattern density related the threading dislocation. Furthermore, we report the process technology and optimized the implanted energy, dose, and the position of dislocation sink in Si1-xGex/Si structure via ion implantation. * This work was financially supported by the Brain Korea 21 Plus Program in 2015 and SiWEDS (Silicon Wafer Engineering and Defect Science). Reference [1] J. G. Park et al., Mat. Sci. Eng. B 134142-153 (2006) [2] S. Takagi, Strained-Si CMOS Technology in Advanced Gate Stacks for High-Mobility Semiconductors, Springer Berlin Heidelberg 1 (2007) Figure 1

Dislocations in CdTe heteroepitaxial structures on GaAs(301) and Si(301) substrates

Initial stages of ZnTe growth on GaAs(301) and Si(301) substrates by the method of molecular beam epitaxy are investigated by means of in situ one-wave ellipsometry. Layer-by-layer growth of the ZnTe film is observed on GaAs(301) substrates, whereas 3D nucleation occurs during epitaxy on Si(301) substrates. Misfit dislocations (MDs) are inserted into the ZnTe film during the growth of the first monolayers. Owing to MDs, the film lattice turns with respect to the substrate lattice, which is confirmed by X-ray measurements. Threading segments of MDs in CdTe/ZnTe/GaAs(301) and CdTe/ZnTe/Si(301) heterostructures are subjected to etching. The etch dislocation pits are found to have different shapes, which testifies to different types of threading dislocations. In the case of layer-by-layer etching, the dislocation density is found to increase inward the CdTe film, which testifies to annihilation of dislocations in the course of growth of CdTe films. The dislocation annihilation rate is higher in films grown on GaAs(301) than in those grown on Si(301). A possible reason is the higher mobility of dislocations in CdTe films on GaAs(301) substrates.

Directed evolution of α -grains in thin metastable-Al 2O 3 films deposited on Si(100) after post-deposition annealing

A 250-nm-thick Al 2O 3 film was deposited on a Si(100) by a radio-frequency magnetron sputtering and annealed at 1100 °C for various periods of time in air. In the matrix composed of fine metastable-Al 2O 3 grains of 50–100 nm in diameter, large α-Al 2O 3 grains of about 2–10 μm in diameter appeared, interestingly aligning themselves along various directions. The compressive stress developed in the alumina films because the thermal expansion coefficient of the film was higher than that of the silicon substrate. The stress distribution in the film is expected to be inhomogeneous due to some discontinuities or defects, such as arrays of dislocation pits and steps on the surface of the Si substrate, which could be generated by intersections of the substrate surface and the slip and twin planes in the Si substrate. The enhanced phase transformation into α-Al 2O 3 along various directions is suggested to arise from such discontinuities or defects.

Convergence of Microscopy Techniques

Keywords: AlInN,GaN, SEM, TEM, Weak Beam, LACBED Note: Invited paper Reference CIME-ARTICLE-2009-021doi:10.1002/imic.200990042 Record created on 2009-11-09, modified on 2017-05-12

The effect of temperature and ammonia flux on the surface morphology and composition of In xAl 1−xN epitaxial layers

An interesting recent development in the Group III nitrides is the growth of InAlN lattice matched to GaN, with applications in distributed Bragg reflectors (DBRs), high electron mobility transistors (HEMTs) and as etch-layers. This work presents a systematic study of the effects of changing the key growth conditions of ammonia flux and growth temperature in InAlN growth by metal-organic vapour phase epitaxy (MOPVE) and describes our current optimised parameter set. We also particularly concentrate on the details of surface morphology assessed by atomic force microscopy (AFM). The nanoscale surfaces are characterised by low hillocks and dislocation pits, while at a larger scale microscopic indium droplets are also present. However, these droplets are eliminated when the layers are capped with GaN. Other trends observed are that increasing the growth temperature will lower the indium incorporation approximately linearly at a rate of approximately 0.25% per °C, and that increasing the ammonia flux from 44.6 to 178.6 mmol min −1 increased the indium incorporation, but further increases to 446 mmol min −1 did not result in any further increase.

Growth and characterization of Al xGa 1−xN via NH 3-based metal-organic molecular beam epitaxy

Growth and characterization of ammonia-based metal-organic molecular beam epitaxy (NH 3-MOMBE) Al x Ga 1− x N epitaxial films has been conducted. Al x Ga 1− x N films spanning the entire range of aluminum compositions were grown on GaN templates. This is the first reported successful growth of Al x Ga 1− x N via NH 3-MOMBE, using triethylgallium (TEGa), triethylaluminum (TEAl) and ammonia (NH 3) as the precursors. These films were characterized via optical interferometry (OI), atomic force microscopy (AFM), X-ray diffraction (XRD) and scanning electron microscopy (SEM). High-quality Al x Ga 1− x N films, as inferred by XRD, are achievable in films without cracking. The catalytic effect of Al on NH 3 is found to play a major part in the growth rate of the Al x Ga 1− x N films. The excessive nitrogen produced through this catalytic effect hinders the growth rate at lower Al composition while increasing the growth rate of Al x Ga 1− x N ( x>0.4) films. Stress in the deposited films is found to be partially relieved through surface cracking along the 〈1 1 2¯ 0〉 direction in the film. These cracks provide dislocation gettering centers, with the dislocation pit density decreasing with increasing Al composition. A basic understanding on the factors affecting the growth of Al x Ga 1− x N is determined and will become the basis for further investigations into the optimization of Al x Ga 1− x N growth.

Carrier transport and luminescence properties of n-type GaN

The surface morphology, electrical properties and optical properties of Si doped n-type GaN were investigated. The intentional SiH4 doped GaN films were grown by metal organic chemical vapor deposition with the electron concentration varying from 3×1016 cm−3 to 5.4×1018 cm−3. The surface morphology shows that the roughness and dislocation pits increase as the mass flow rate of SiH4 increases, which indicates that the quality of GaN degrades gradually. The activation energy of Si in GaN with different n concentrations varies from 12 to 22 meV, which may originate from the interactions of donor wave functions. The carrier transport mechanism with increasing temperature from 100 to 420 K was concluded as the complex effect of both impurity scattering and phonon scattering. The position of the near band edge emission peak was determined by both renormalization of the band gap and B-M effect. The intensity variations of the yellow luminescence could be explained by the change of Ga vacancy concentration caused by Si doping.

The role of strain in controlling the surface morphology of Al xGa 1− xN following in situ treatment with SiH 4 and NH 3

Treatment of GaN with SiH 4 and NH 3 increases the size of surface pits associated with threading dislocations, allowing them to be easily imaged by atomic force microscopy. Here, we assess the effect of a similar treatment on Al x Ga 1− x N surfaces for x ≤ 0.4. For relaxed Al x Ga 1− x N epilayers, an increase in the observed size and density of threading dislocation pits is observed. However, if the Al x Ga 1− x N is under tensile strain, the treatment results in the appearance of nanometre-scale surface hillocks. These hillocks may prevent observation of the dislocation pits. The hillocks are found to consist of crystalline Al x Ga 1− x N, and hence are suggested to be formed by strain driven etching or transformation of the surface by SiH 4 and NH 3.

Highlighting threading dislocations in MOVPE-grown GaN using an in situ treatment with SiH 4 and NH 3

Fast-turnaround, accurate methods for the assessment of threading dislocation (TD) densities in GaN are an essential research tool. Here, we present an in situ surface treatment in which GaN is exposed to a SiH 4 flux at 860 °C in the presence of NH 3. Following a 240 s exposure to SiH 4, pits associated with screw or mixed-type TD were found to have more than doubled in diameter, as measured by atomic force microscopy (AFM). These pits are associated with step-edge terminations. Additional small pits had appeared, not associated with step-edge terminations, which are believed to relate to edge-type TDs. The total density of pits on the treated surface corresponded to the total dislocation density measured by transmission electron microscopy. Pits related to edge-type TDs are often overlooked in AFM of untreated GaN. As the SiH 4 treatment time is increased, the measured dislocation density initially increases, but after a 240 s treatment all the TDs may be observed. The pit width initially increases with treatment time, but then plateaus. The SiH 4 treatment is effective in increasing dislocation pit size on both n- and p-type material, and has also been used on partially coalesced GaN layers.