Synchrotron Monochromatic Beam X-ray Topography Research Articles

Analysis of Basal Plane Dislocation Motion Induced By P+ Ion Implantation Using Synchrotron X-Ray Topography

Silicon Carbide (SiC) is a promising wide bandgap semiconductor for future power devices since it has a wide bandgap, high breakdown voltage and good thermal stability [1]. The most mature method to perform selective area doping in 4H-SiC epiwafers during fabrication is ion implantation [2]. However, such implantation processes employing high energy ions can damage the lattice in the epilayers that can subsequently lead to formation and migration of basal plane dislocations (BPDs) which are known to be detrimental to the performance of the devices [3-4]. Implantation processes are typically conducted under room temperature (RT) conditions, but high temperature (HT) implantation is favorable when the dose level is high [5]. Oxide layer for blocking purpose is inevitable since photoresist can barely remain intact under such high temperature, which will increase the time, cost, and complexity [6-7].Here, we will primarily emphasize the motion of the BPDs under stress from RT implantation. 1.2 kV-rated 4H-SiC PiN diodes with junction termination extension (JTE) annealed with same conditions have been successfully fabricated by implantation with different dose levels and concentration profiles under room temperature and at 600 ˚C. Concentration profiles simulated by Stopping and Range of Ions in Matter (SRIM) are shown in Fig.1(a) [8]. The JTEs were implanted with lower concentrations. Synchrotron monochromatic beam X-ray topography (SMBXT) has been performed to characterize the defects induced by implantation and annealing process. Topographs of PIN diodes are shown in Fig.1 (b)-(h). For the diodes implanted with 1x under RT and HT, there is no evidence of dislocations generated due to implantation and annealing. However, formation of BPD half loops, as highlighted in the red and yellow boxes, can be observed from the edge of the device when the dose level is elevated to 5x and 9x. In addition to that, the basal plane density (BPD) density of 5x RT Box due to implantation and annealing is much more significant than that of 5x RT and 9x RT, indicating that concentration profile can affect the defect generation. Fig.1 (e) shows topograph of PiN diode implanted with 5x under high temperature. The absence of BPDs compared to the RT implanted device to the same concentration profile suggests the generation of BPD is suppressed by the high temperature condition. In 5x RT Box device, opposite sign BPDs are nucleated from opposite edges of device, as indicated in Fig.1 (f)&(g). Here, we will analyze the motion of dislocations generated by ion implantation and annealing.Reference:[1] J. Guo, Y. Yang, B. Raghothamachar, T. Kim, M. Dudley, J. Kim, J. Cryst. Growth[2] F. Roccaforte, P. Fiorenza, M. Vivona, G. Greco, F. Giannazzo, Materials 14(14) (2021) 3923.[3] K. Konishi, R. Fujita, Y. Mori and A. Shima, Semiconductor Science and Technology 2018 Vol. 33 Issue 12[4] M. Nagano, H. Tsuchida, T. Suzuki T. Hatakeyama, J. Senzaki and K. Fukuda, J. Appl. Phys. 108, 013511 (2010)[5] S. Mancini, S. Y. Jang, Z. Chen, D. Kim, Y. Liu, B. Raghothamachar, M. Kang, A. Agarwal, N. Mahadik, R. Stahlbush, M. Dudley, W. Sung, proceeding of 2022 IEEE International Reliability Physics Symposium (IRPS). (accepted)[6] T. Kimoto, J. A. Cooper. John Wiley & Sons Singapore Pte. Ltd. 2014. pp. 197-200[7] D. Kim, N. Yun and W. Sung, 2021 IEEE International Reliability Physics Symposium (IRPS), 2021, pp. 1-4, doi: 10.1109/IRPS46558.2021.9405109[8] J. F. Ziegler, M.D. Ziegler, J.P. Biersack, Nucl Instrum Methods Phys Res B, Volume 268, Issues 11–12, June 2010, Pages 1818-1823 Figure 1

Investigation of defect formation at the early stage of PVT-grown 4H-SiC crystals

Several 4° off-axis 4H-SiC wafers with several hundred microns of initial-stage growth by PVT method are investigated by Synchrotron Monochromatic Beam X-ray Topography (SMBXT). Defect behavior across the seed/newly grown layer interface are demonstrated. Comparison of early stage grown layers to seed sample indicates generation of threading edge dislocation (TED) and threading screw dislocation (TSD)/ threading mixed dislocation (TMD) pairs at the interface while most basal plane dislocations (BPDs) are deflected into TEDs. The (0001) facet of the crystal is already formed at early stage growth at the edge of the wafer and high nitrogen incorporation in facet leads to conditions favorable for nucleation and glide of Shockley/double Shockley faults with layers of 3C-SiC deposited on facet acting as nuclei. Unique-shaped dislocations are observed at early stage growth, which are caused by deflection of TSDs/TMDs and TEDs by macrosteps near the periphery of the sample and the subsequent glide of the a components. The effect of the quality of the seed surface before growth is manifested as randomly oriented arrays of pairs of TEDs and TSDs/TMDs on the as grown surface resulting from residual surface damage from scratches.

(Invited) Application of Synchrotron X-Ray Topography Techniques to the Analysis of Defect Microstructures in Bulk GaN Substrates and Epilayers for Power Devices

The study of defects and strain in GaN substrates and epilayers for vertical device development using synchrotron X-ray topography techniques is presented. Synchrotron monochromatic beam X-ray topography (SMBXT) studies show that ammonothermal-grown GaN substrate wafers have the lowest dislocation densities while patterned hydride vapor phase epitaxy (HVPE) GaN reveal a starkly heterogeneous distribution of dislocations with large areas containing low threading dislocation densities and HVPE GaN substrates contain high dislocation densities. Epitaxial growth does not nucleate new defects but interactions of dislocations with point defects can cause changes in dislocation configurations. Rocking curve Analysis by Dynamical Simulation (RADS) is shown to be effective in analysis of implantation by correlating the depth profile of strain with the doping profile. Removal of lattice damage induced by implantation requires annealing with proper capping or under high pressures to limit loss of material and lattice distortion. Inductively coupled plasma (ICP) etching may introduce strain in GaN material that can be partially recovered by TBCl etching. Diffusion doping does not introduce new strains in GaN material while neutron transmutation doping at low levels can lead to curing of defects while higher levels lead to irradiation damage and nucleation of new defects.

Ray-Tracing Simulation Analysis of Effective Penetration Depths on Grazing Incidence Synchrotron X-Ray Topographic Images of Basal Plane Dislocations in 4H-SiC Wafers

Understanding the depth from which contrast from dislocations is still discernible (the effective penetration depth of the X-rays) in grazing-incidence synchrotron monochromatic beam X-ray topography is of great interest as it enables three-dimensional dislocation configuration analysis and accurate density calculations. To this end, systematic analysis has been performed of topographic and ray-tracing simulated contrast of basal plane dislocations with different Burgers vector and line direction combinations, and a universal method to determine the effective penetration depth based on ray tracing has been developed. This study reveals that the observable dislocation contrast depends on the effective misorientation associated with the dislocation modulated by the photoelectric absorption effect. The dislocations with larger effective misorientation tend to have longer projected length and correspondingly deeper effective penetration depths.

Dislocation Contrast Analysis in Weak Beam Synchrotron X-Ray Topography

Synchrotron monochromatic beam X-ray topography has been widely applied to characterize structural defects in SiC crystals. Using ray tracing simulations, the dislocation contrast in X-ray topography under strong diffraction conditions (diffraction takes place at or near Bragg angle) has been intensively investigated. However, the contrast and the configurations of the dislocation images recorded under weak diffraction conditions have not been fully investigated. Recently, we demonstrated that the contrast of dislocations in synchrotron grazing incidence topography under weak diffraction conditions can also be analyzed and interpreted by applying ray tracing principles. In this study, we have extended the application of the ray tracing method to analyze the dislocation contrast in weak beam synchrotron back reflection and rocking curve topography. The ray tracing method is shown to successfully simulate and correlate the contrast of threading screw dislocations at various positions on the rocking curve and thus allow to determine the signs of Burgers vectors.

Microstructure Analysis of GaN Epitaxial Layers During Ion Implantation Using Synchrotron X-Ray Topography

Power electronic devices based on wide band-gap semiconductor materials such as GaN and SiC are rapidly being developed to replace traditional silicon-based devices whose performance has nearly reached their material limits. In the fabrication of GaN vertical power devices, selective area doping (SAD) processes are essential [1]. Several SAD techniques have been developed, including ion implantation [2], etching and regrowth method [3, 4], diffusion doping and neutron transmutation [5]. However, the influences of these procedures on the microstructures of GaN epitaxial layers is one of the key factors to determine the performance of the devices.In this study, ion-implanted GaN epitaxial layers from different stages including ammonothermal grown substrate material, metal organic chemical vapor deposition (MOCVD) epitaxial growth, ion implantation and subsequent annealing was characterized by synchrotron monochromatic beam X-ray topography (SMBXT) [6], synchrotron X-ray rocking curve topography (SXRCT) [7], and high-resolution X-ray diffraction (HRXRD). The change of distribution of threading dislocations (TDs) is characterized. The comparison of lattice strain of the material from each processing stage is conducted by both HRXRD and SXRCT.Enlarged contrast of screw and edge types of threading dislocations (TDs) on X-ray topographs after homoepitaxial growth is observed and likely due to interaction with point defects. X-ray topographs reveal ion implantation does not change the distribution of dislocations in the wafer. Strain and tilt maps derived from X-ray rocking curve topographs also show that annealing leads to an improvement in lattice bending levels. These results will be discussed with their implications for further processing into devices.

Microstructure Analysis of GaN Epitaxial Layers During Ion Implantation Using Synchrotron X-Ray Topography

A study on characterization of microstructures in ammonothermal grown GaN wafers at different stages of device fabrication is conducted using synchrotron monochromatic beam X-ray topography (SMBXT), synchrotron X-ray rocking curve topography (SXRCT) as well as high resolution X-ray diffraction (HRXRD). Synchrotron monochromatic beam X-ray topographs reveal the various dislocation types and their distribution in the GaN wafer at different processing stages remains the same except that the contrast of threading dislocations is enlarged or darkened. HRXRD spectra of the ion implanted wafer reveals satellite peak and fringes from lattice damage. Rocking Curve Analysis by Dynamical Simulation (RADS) that fits the spectra gives a depth profile of strain correlated well to the designed implantation profile. This damage is completely healed after annealing process at 1225 ℃. Strain and tilt maps generated from SXRCT show an improvement in lattice bending level during annealing.

Characterization of Dislocations in 6H-SiC Wafer Through X-Ray Topography and Ray-Tracing Simulations

Silicon carbide (SiC) is an important semiconductor material for a variety of electronic and optoelectronic applications owing to the unique combination of its superior electronic and physical properties. In order to continuously improve the crystal quality and improve device performance, obtaining a clear understanding of the defect types and their distribution and potential influence on device operation is of great importance. In this study, 6H-SiC crystals grown by physical vapor transport (PVT) have been characterized by synchrotron monochromatic beam x-ray topography (SMBXT). By recording six different $$11{\bar{2}},12$$ grazing incidence reflections and analyzing the contrast patterns of threading screw dislocations (TSDs), threading edge dislocations (TEDs), threading mixed dislocations (TMDs), and basal plane dislocations (BPDs) observed in conjunction with ray-tracing simulation, the Burgers vectors of these dislocations have been determined. This successfully demonstrated a direct Burgers vector determination approach for each type of dislocation. Understanding these dislocation types and their distributions in 6H-SiC wafers can provide crucial feedback for pursuing crystal quality enhancement during growth process. High-resolution x-ray diffraction (HRXRD) has been performed on the wafer to carry out the rocking curve analysis of areas with different degrees of lattice distortion.

Characterization of Dislocations in 4H-SiC Single Crystals at the Initial Growth Stage by Synchrotron X-ray Topography

In recent years, 4H-SiC has become a widely acknowledged material applied in high power electronics. 4H-SiC-based devices are able to operate at high voltage, high current and high temperature due to its superior physical properties. However, they have yet to reached to the requirements for mass production, due to the fact of SiC’s relatively inferior crystal quality. Over the past few decades, the effect of various dislocations existing in the crystals such as threading screw/mixed dislocations (TSD/TMDs), threading edge dislocations (TEDs) and basal plane dislocations (BPDs) has been studied and revealed to be main source for degrading the reliability of SiC power devices[1-2]. Recently, studies on the early stages of physical vapor transport (PVT) growth of SiC have been reported by several groups regarding to the investigation of the step morphology and lattice plane bending [3-5]. However, dislocation propagation behavior and their formation mechanism at the early growth stages are yet to be studied in detail.This paper describes the investigation of dislocation behavior during the early stages of PVT-grown 6-inch 4H-SiC crystals by synchrotron monochromatic beam x-ray topography (SMBXT) technique. Ray tracing simulation was applied to simulate the dislocation images. Our studies show that most of the TSDs/TMDs are replicated into the newly grown crystal while most TEDs are generated by either nucleation in pairs at the seed/crystal interface or by redirection of BPDs in the seed crystal. Most BPDs in the newly grown layer are of screw type with 1/3[11-20] and this has been verified by comparison with ray tracing simulated images. TEDs with the same and opposite sign of Burgers vector are found to be deflected on to same basal plane by the overgrowth of macro-steps and start to glide in the same and opposite directions respectively. TMDs deflected on to the basal plane by macro-steps get dissociated into c and a components, with the a segment undergoing glide to form V-shaped configurations.[1] St.G. Muller, J.J. Sumakeris, M.F. Brady, R.C. Glass, H.M. Hobgood, J.R. Jenny, R. Leonard, D.P. Malta, M.J. Paisley, A.R. Powell, V.F. Tsvetkov, S.T. Allen, M.K. Das, J.W. Palmour, and C.H. Carter. Jr., Eur. Phys. J. Appl. Phys. 27, 29 (2004).[2] R. Singh and M. Pecht, IEEE Ind Electron M 2, 19 (2008).[3] E.K. Sanchez, J.Q. Lin, M.De. Graef, M. Skowronski, W.M. Vetter, M. Dudley, J. Appl. Phys. 91 (3) (2002) 1143.[4] C. Ohshige, T. Takahashi, N. Ohtani, M. Katsuno, T. Fujimoto, S. Sato, H. Tsuge, T. Yano, H. Matsuhata, M. Kitabatake, J. Cryst. Growth 1-6, 408 (2014).[5] N. Ohtani, C. Ohshige, M. Katsuno, T. Fujimoto, S. Sato, H. Tsuge, W. Ohashi, T. Yano, H. Matsuhata, M. Kitabatake, J. Cryst. Growth 9-15, 386 (2014). Figure 1

Synchrotron X-ray Topography Characterization of Commercial GaN Substrates for Power Electronic Applications

As one of the most important wide bandgap semiconductors, Gallium Nitride (GaN) has many applications in power electronic devices such as inverters and switches, as well as optoelectronic devices like light emitting diodes.[1] However, high-quality bulk GaN growth is still limited by the availability of growth techniques. Two most popular growth method for GaN are hydride vapor phase epitaxy (HVPE) [2, 3] and ammonothermal [4, 5] method. HVPE method uses foreign substrates, such as sapphire, gallium arsenide or silicon carbide, which gives a large dislocation density due to significant lattice mismatch and difference in coefficients of thermal expansion. However, in ammonothermal method, native seeds were used to minimize the effects of lattice mismatch and a retrograde direction of GaN transport inside the growth system was utilized to exclude most of the contamination and undesirable phases. So, ammonothermal method gives a much better quality.In this study, GaN substrates of both HVPE (Figure 1) and ammonothermal (Figure 2) methods have been characterized by synchrotron monochromatic beam X-ray topography (SMBXT)[6]. The distribution of threading screw/mixed dislocations (TSDs/TMDs), threading edge dislocations (TEDs) and basal plane dislocations (BPDs) is characterized. Ray tracing simulations are adopted to confirm the types of dislocations. The comparison of defect distribution between HVPE and ammonothermal samples has been conducted by both SWBXT and High-resolution X-ray Diffraction (HRXRD).

Analysis of Dislocations in PVT-Grown 6H-SiC through Grazing-Incidence X-Ray Topographic Images and Ray-Tracing Simulation

The superior electronic and physical properties of silicon carbide (SiC) enabled successful applications in electronic and optoelectronic applications. Therefore, understanding the nature and behavior of different dislocations is of great significance towards crystal quality enhancement and device degradation prevention. In this study, synchrotron monochromatic beam X-ray topography (SMBXT) analysis was carried out on a PVT-grown 6H-SiC wafer for recording its grazing-incidence images of all six different 1 1 2‾12 reflections. The distribution of TSDs, TEDs, TMDs and BPDs has been observed on topographic images, and characterized through correlation with ray-tracing simulation. The conjunction of topographic and simulated images in this study has successfully accomplished a direct Burgers vectors determination approach for each type of dislocations, which can provide crucial information for quality improvement of crystal.

Characterization of Dislocations in 4H-SiC Single Crystals at the Initial Growth Stage by Synchrotron X-ray Topography

This paper describes the investigation of dislocation behavior during the early stages of PVT-grown 6-inch 4H-SiC crystals by synchrotron monochromatic beam x-ray topography technique. Ray tracing simulation is applied to simulate the dislocation images. Our studies show that most TSDs/TMDs are replicated into the newly grown crystal while most TEDs are generated by either nucleation in pairs at the seed/crystal interface or by redirection of BPDs in the seed crystal. Most BPDs in the newly grown crystal are of screw type with 1/3 [112‾0], which is verified by comparison with the simulated images. TEDs with the same and opposite sign of Burgers vector are found to be deflected onto the same basal plane by the overgrowth of macro-steps and glide towards to the same or opposite directions respectively. TMDs deflected onto the basal plane get dissociated into a and c components, with the a segment undergoing glide to form V-shaped configurations.

Synchrotron X-Ray Topography Study on the Relationship between Local Basal Plane Bending and Basal Plane Dislocations in PVT-Grown 4H-SiC Substrate Wafers

Synchrotron monochromatic beam X-ray topography (SMBXT) in grazing incidence geometry shows black and white contrast for basal plane dislocations (BPDs) with Burgers vectors of opposite signs as demonstrated using ray tracing simulations. The inhomogeneous distribution of these dislocations is associated with the concave/convex shape of the basal plane. Therefore, the distribution of these two BPD types were examined for several 6-inch diameter 4H-SiC substrates and the net BPD density distribution was used for evaluating the nature and magnitude of basal plane bending in these wafers. Results show different bending behaviors along the two radial directions - [110] and [100] directions, indicating the existence of non-isotropic bending. Linear mapping of the peak shift of the 0008 reflection along the two directions was carried out using HRXRD to correlate with the results from the SMBXT measurements. Basal-plane-tilt angle calculated using the net BPD density derived from SMBXT shows a good correlation with those obtained from HRXRD measurements, which further confirmed that bending in basal plane is caused by the non-uniform distribution of BPDs. Regions of severe bending were found to be associated with both large tilt angles (95% black contrast BPDs to 5% white contrast BPDs) and abrupt changes in a and c lattice parameters i.e. local strain.

Investigation of Dislocation Behavior at the Early Stage of PVT-Grown 4H-SiC Crystals

Dislocation behavior during the early stages of physical vapor transport (PVT) growth of 6-inch diameter 4H-SiC crystals has been investigated by synchrotron monochromatic beam X-ray topography (SMBXT) in conjunction with ray tracing simulations of dislocation images. Our studies reveal that most of the TSDs/TMDs are replicated into the newly grown layer while most TEDs are generated by either nucleation in pairs at the growth interface or by redirection of BPDs in the seed crystal. Most BPDs in the newly grown layer are of screw type with and this has been verified by comparison with ray tracing simulated images. TEDs with same and opposite sign of Burgers vector are found to be deflected on to the same basal plane by the overgrowth of macro-steps and they glide in the same and opposite directions respectively. TMDs deflected on to the basal plane by macro-steps get dissociated into c and a components, with the a segment undergoing glide to form V-shaped configurations.

X-ray topography characterization of gallium nitride substrates for power device development

Gallium nitride substrates grown by the hydride vapor phase epitaxy (HVPE) method using a patterned growth process have been characterized by synchrotron monochromatic beam X-ray topography in the grazing incidence geometry. Images reveal a starkly heterogeneous distribution of dislocations with areas as large as 0.3 mm2 containing threading dislocation densities below 103 cm−2 in between a grid of strain centers with higher threading dislocation densities (>104 cm−2). Basal plane dislocation densities in these areas are as low as 104 cm−2. By comparing the recorded images of dislocations with ray tracing simulations of expected dislocations in GaN, the Burgers vectors of the dislocations have been determined. The distribution of threading screw/mixed dislocations (TSDs/TMDs), threading edge dislocations (TEDs) and basal plane dislocations (BPDs) is discussed with implications for fabrication of power devices.

Relationship Between Basal Plane Dislocation Distribution and Local Basal Plane Bending in PVT-Grown 4H-SiC Crystals

The inhomogeneous distributions of basal plane dislocations (BPDs) in PVT-grown 4H-SiC crystal boule due to internal stresses cause lattice plane bending, which strongly affect SiC-based device fabrication. The relationship between BPDs and local basal plane bending in 6-inch 4H-SiC substrates has been investigated. Synchrotron monochromatic beam x-ray topography (SMBXT) imaging shows black and white contrast of BPDs with Burgers vectors of opposite signs based on the principle of ray tracing. We have evaluated the net difference of BPDs with black and white contrast along both [11$$ \bar{2}$$0] and [1$$ \bar{1}$$00] radial directions on the Si face across multiple 6-inch diameter 4H-SiC substrates sliced from the same and different boules and predicted the nature (concave/convex) and amount of bending of the basal plane in these wafers. Line scans of 0008 reflection using high resolution x-ray diffractometry (HRXRD) has been carried out along the two directions to verify the nature of bending in these wafers. Results show quite different bending behavior along [11$$ \bar{2} $$0] and [1$$ \bar{1}$$00] directions, indicating that the Si face of 6-inch substrates creates non-isotropic bending on the basal plane. These observations are correlated quite well with net BPD density analysis. The physical shapes of the wafers were also measured to be not flat due to the surface effect. Quantitative analysis of the degree of basal plane bending based on the SMBXT data was carried out and found to be correlating well with the measured tilt angle from HRXRD. Existence of a high stress center was observed in one of the 6-inch wafers resulting in severe bending which is associated with both large bending angles and abrupt changes in lattice constants a and c.

Relationship between Basal Plane Dislocation and Local Basal Plane Bending in PVT-Grown 4H-SiC Crystals

Efforts to improve the quality and size of 4H-SiC wafers have resulted in size of 6” and dislocation densities of the order of 103 cm-2. The presence of significant quantities of crystallographic defects in bulk 4H-SiC crystals continues to be a major obstacle for achieving high-quality 4H-SiC substrates. Of particular note is the nucleation and distribution of basal plane dislocations (BPDs). BPDs are deformation-induced and are mostly generated during post-crystal growth cooling or high temperature annealing processes. BPDs have been associated with the formation of Shockley stacking fault leading to an increase in forward voltage degradation and are undesirable. Depending on the PVT growth conditions, internal stresses due to non-uniformity of temperature field cause lattice plane bending. During cooldown, this bending is accommodated by the inhomogeneous distribution of BPDs in a PVT grown 4H-SiC boule and persists in wafers sliced from the boule. Crystal bending affects subsequent wafer processing especially polishing and device fabrication. Therefore, analysis of the BPD distribution (sign and density) enables us to better understand basal plane bending, which provides insight into further improvement of the crystal growth process. Synchrotron Monochromatic Beam X-ray Topography (SMBXT) studies in grazing incidence geometry reveal the appearance of black and white contrast of BPDs which are associated with opposite sign of Burgers vectors. Based on the principle of ray tracing, black contrast BPDs are generated by focusing of diffracted X-rays when the extra half plane is extending away from the imaged surface, while defocusing of X-rays contribute to the generation of white contrast BPDs due to the extra half plane extending towards the surface [1]. The inhomogeneous distribution of the two types of BPD contrast will thus result in concave/convex shape of the basal planes. In our study, we have evaluated the ratio of the black/white contrast of BPDs along 11-20 direction across multiple 6-inch diameter 4H-SiC substrates sliced from the same and different boules and predicted how the lattice is tilted in different substrate wafers. High resolution X-ray diffraction measurements are currently underway to investigate the variation of rocking curve peak shift along 11-20 direction and thus to further verify our result.

Relationship between Basal Plane Dislocation and Local Basal Plane Bending in PVT-Grown 4H-SiC Crystals

Synchrotron monochromatic beam x-ray topography (SMBXT) shows black and white contrast of BPDs for Burgers vectors of opposite signs based on the principle of ray tracing. We have evaluated the ratio of black and white contrast of BPDs along both [1120] and [1100] directions across multiple 4-inch and 6-inch diameter 4H-SiC substrates. Results show the predominance of white contrast BPDs along both radial directions indicating that the basal planes on Si face are bent in a convex manner. Line scans of 0004 reflection using HRXRD was carried out which further confirmed the nature of basal plane bending in these wafers. Detailed analysis on the subsequent wafers across the crystal boule reveals the inheritance of basal plane bending behavior in these wafers. The radius of curvature in 6-inch wafers was found to be larger than the 4-inch wafers. Additional studies on the effect of low angle grain boundaries were also discussed.

High Quality AlN Single Crystal Substrates for AlGaN-Based Devices

Aluminum nitride (AlN) single crystal boules were grown by physical vapor transport (PVT). Diameter expansion during boule growth, without the introduction of low angle grain boundaries (LAGB) around the boule periphery, was confirmed by crossed polarizer imaging, synchrotron white beam x-ray topography (SWBXT), and synchrotron monochromatic beam x-ray topography (SMBXT). The densities of basal plane dislocations (BPD) and threading edge dislocations (TED) averaged from high-magnification topographs of five regions of a high-quality substrate were 0 cm-2 and 992 cm-2, respectively. Substrates fabricated from AlN boules possessed excellent surface finishes suitable for epitaxy.

Observation of Threading Dislocations in Ammonothermal Gallium Nitride Single Crystal Using Synchrotron X-ray Topography

Synchrotron monochromatic-beam x-ray topography observation has been performed on high-quality ammonothermal gallium nitride single crystal to evaluate threading dislocations (TD) in a nondestructive manner. Asymmetric diffractions with six equivalent g-vectors of 11–26, in addition to a symmetric diffraction with g = 0008, were applied to determine the Burgers vectors (b) of dislocations. It was found that pure edge-type TDs with \( {\varvec b} = \left\langle {11 - 20} \right\rangle /3 \) did not exist in the sample. A dominant proportion of TDs were of mixed type with \( {\varvec b} = \left\langle {11 - 20} \right\rangle /3 + \left\langle {0001} \right\rangle \), i.e., so-called c + a dislocations. Pure 1c screw dislocations with \( {\varvec b} = \left\langle {0001} \right\rangle \) and TDs with c-component larger than 1c were also observed.