Microwave microscopy of diamond semiconductor structures A.N. Reznika, S.A. Korolyov, and M.N. Drozdov Institute for Physics of Microstructures of the Russian Academy of Sciences, GSP-105, Nizhniy Novgorod, 603950, Russia Scanning near-field microwave microscope (SNMM) was used to study resistance Rsh of a boron delta-doped epilayer of diamond grown on an HPHT substrate. Measurements were performed with a ~1.4 GHz working frequency, and ~85 μm space resolution microscope on samples with the lateral dimensions of 33 mm2. Some substrates featured a crystalline structure defect over which the epilayer resistance Rsh was seen to increase by more than an order for ~1 mm linear dimensions of the high-ohmic region. The SNMM measurements data revealed some substrates to have nonuniform conductivity, i.e., a high-ohmic area in the central part surrounded by a conducting edge region. In the latter case the SNMM method allowed determining a surface distribution of epilayer resistance Rsh, undistorted by the shunting influence of the substrate. Reliability of the SNMM results is confirmed by the local four-probe resistance measurements. At the same time, the alternative methods such as non-local van der Pauw method and secondary ion mass spectroscopy failed to detect nonuniformity of the structure conducting properties, established by SNMM. The obtained values for hole concentration Np ≈ 1.71020 cm-3 and mobility μН ≈ 15 cm2/(V s) are assumed to possibly pertain to the diamond delta-layer.
Introduction Present-day manufacturing technologies for devices and elements of semiconductor micro- and nanoelectronics involve characterization of samples in a variety of methods and techniques. Among the most widely used ones are secondary ion mass spectroscopy (SIMS), capacitance versus voltage C(V) measurements, Hall effect combined with four probe resistivity measurements (commonly named as van der Pauw (VDP) method), optical ellipsometry, electron microscopy, infrared Fourier spectroscopy, probe microscopy, X-ray structural analysis and many others. Simultaneous application of several probing techniques allows one to get more information on structures in question. Moreover, to upgrade the data reliability it is useful to employ tools that will ensure determination of similar parameters (for example, conducting or structural properties) through independent measurements. In this connection of great potential value are non-traditional methods that are currently under development and testing. Of these a very promising technique is scanning near-field microwave microscopy (SNMM) [1-3]. This method is characterized by a high resolving power that exceeds the working wavelength by many orders of magnitude. Modern microscopes in the centimeter and decimeter wave range are capable of nanometer resolution [4-7] down to the atomic scale [8]. Yet, a great amount of research so far has been done based on medium resolution (1-103 μm) devices [9-20]. The important advantages of SNMM rest on its capability for non-invasive nondestructive probing of objects not only on the surface, but also in depth. Another essential characteristic is high sensitivity of the microscope to the conducting properties of material. In the last 15-20 years considerable success has been achieved in quantitative SNMM diagnostics [9-11,20-25], making it possible to demonstrate the characterization potentialities for semiconductors of yet a fairly simple structure – bulk homogeneous or thin film ones [6,16,20,24,26]. These achievements give reason to believe that SNMM can find a wider application in semiconductor technologies. The key direction in the SNMM development over the recent years has been towards achieving extremely high (nanometer and subnanometer) spatial resolution, being called for by the corresponding size of today’s electronics components. It seems, there is an appropriate area of application for mediumresolution SNMM as well, in particular, in working-out manufacturing technologies for new semiconductor materials. One promising material under active investigation recently is semiconductor diamond [27]. It is expected that the predicted outstanding properties of diamond (large carrier mobility, high breakdown voltage, and exceptional thermal conductivity) will help improve the characteristics of semiconductor a
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devices for high power and high frequency electronics. Main problems of semiconductor diamond fabrication technology now include producing large-size (> 25 mm) single crystal diamond substrates, attaining high values of free-carriers concentration (> 5×1020 cm-3) and mobility (> 103 cm2/(V s)), forming ultra-thin conducting layers (< 2 nm) by delta-doping, realizing surface-homogeneous characteristics of structures. Today’s single-crystal diamond substrates are not more than 15 mm in size. Due to high cost of the substrates studies are usually conducted on samples of much smaller lateral dimensions (the standard size is 33 mm2), which is quite an obstacle for microwave diagnostics. Of widest use are the substrates grown by the temperature gradient method at high pressure and high temperature (HPHT) [28, 29]. The HPHT substrates, depending on the growth parameters, differ in their crystalline quality and impurity content; they may have growth sectors [30] and other structural defects. Substrate defects tell on the structural and electrical properties of epilayers that grow on them [31-33]. Therefore, epitaxial growth has to be controlled by local measurements. In this paper we show that a medium-resolution SNMM can serve as an effective tool for quantitative diagnostics of such structures. Samples and methods Diamond structures were grown on [100]-oriented HPHT substrates with a lateral size of ≈33 mm2. We studied samples with boron p-doped delta-layers of 2-4 nm thickness. Delta-doping of diamond proceeded during epitaxial growth in a microwave plasma-enhanced chemical vapor deposition (MPCVD) reactor with a rapid gas switching system [34]. A typical thickness of the epilayers was ~100 nm, although some samples had a 10-20 nm epilayer. Diborane (B2H6 gas) was used as a source of boron. Along with the SNMM we also used the standard techniques for characterization of semiconductor structures, such as SIMS and VDP method. The SIMS method was used for measuring a depth profile of boron atoms concentration NB(z) on a TOF.SIMS-5 setup. A series of test structures – diamond layers implanted with 50 keV boron ions 11В in a varying dose – were fabricated for boron sensitivity calibration. The VDP method [35, 36] yields holes concentration Np and mobility μH within the epitaxial film-substrate system. In this study we used two geometries of VDP measurements, specifically, the sample geometry (VDP-S) and the local lamella-type geometry (VDP-L). For VDP-S measurements four ohmic contacts were formed in the corners of a test sample. In the VDP-L technique five lamellar specimens were shaped on a sample surface as electrically isolated Hall crosses, i.e., outside the crosses the epilayer was removed. Each cross had four ohmic contacts formed in its corners (see inset in Fig. 5(a)). The overall size of a cross was 0.45×0.45 mm2, but the characterization target was a 0.15×0.15 mm2 area in the center of the cross. The crosses arrangement on a sample surface is shown in the insets in Figs 3(b), 5(a) and 5(b). Unlike the SNMM, the VDP-L method involves several technological operations to be performed during specimens fabrication, and the epitaxial film has to be etched off almost completely. Also note that VDP-S measurements caused destruction of the doped film in the region where conducting contacts were formed with linear dimensions of ~200-300 μm. The same is true for SIMS measurements whose by-effect on a sample is formation of a ~100 μm diameter crater on its surface. Our microwave microscope design is described in Ref. [20], where we also provide detailed information on the technique for determining resistance Rsh of a semiconductor film on a dielectric substrate. The microscope is essentially a 1.4 GHz coaxial λ/2 resonator with a probe in the form of a sharpened tip, connected to the end of the resonator central conductor. The informative parameters used to determine the value of Rsh, are a shift of resonance frequency f and a change in the Q-factor when the probe comes in contact with sample. Resistance Rsh is calculated within the model of an SNMM probe proposed in Ref. [20], which is basically a monopole antenna. The fitting parameters for the model are sought using a series of calibration etalons – dielectric quartz (EQ), sapphire (ES) and conductive silicon plates varying in a doping degree. For the studied diamond structures it was enough to use two highest-resistance Si plates with resistivity ρ = 6000, 52 Ω cm (etalons Е0, E1). The plates thicknesses were 0.4 - 0.7 mm. The microscope resolution power depends on diameter dt of the probe tip end; according to the micrography data dt ≈ 40 μm. The actual resolution was found from measurements of parameters f, Q by scanning a sample surface on which the metal and dielectric regions were divided by a sharp line. The obtained value for resolution d ≈ 85 μm proved to be poorer than expected from dt measurements. In study of diamond 2
samples the probe tip was scanned over sample surface {х, у} along axis х (at y = const) with a step Δх ~ d. In every point of the surface the tip was brought in a ‘soft’ contact with the sample and then moved off the surface to a fixed height Δz = 0.3 μm, as described in Ref. [20]. We measured the microscope resonance curve (frequency dependence of resonator reflectivity), upon which the probe was withdrawn to a certain height z, moved one step Δх along the surface, and the positioning/measuring procedure was repeated. According to the test measurements data from [20] and some additional studies, the error of Rsh measurements with our coaxial SNMM does not exceed 50% at Rsh > 1 kΩ/sq. Unlike in Ref. [20], we used the method developed therein to determine resistance Rsh of epilayer on a conducting substrate and to measure resistivity ρ of the substrate itself. Generalization of the method [20] to these situations does not cause any difficulties. It is suitable for testing planar structures of any complexity, with one parameter to be determined, Rsh or ρ. The complex permittivity and thickness of all other layers in the structure must be known. The SNMM model underlying this technique allows calculation of informative parameters f and Q (i.e., solution of the direct problem) for a structure with any finite number of layers. To determine the single unknown parameter of the structure (solution of the inverse problem) we have designed a special computer algorithm enabling partial automation of the measurement technique. It is obvious that our approach assumes homogeneity of the test structure on scale d, i.e., the characteristic scale of lateral inhomogeneity of parameters Rsh and ρ must be larger than d. As a first example of SNMM measurements, Fig.1 represents dependences of resonance frequency f and Q factor on coordinate x along scan lines 1-3 for sample De1. It is a structure with an epilayer of thickness 80 nm including five delta-layers varying in a peak concentration of boron atoms. A SIMS depth profile of concentration NB(z) is shown in Fig.4(a). Profiles f(x), Q(x) in Figs 1(a) and 1(b) characterize the inhomogeneity of structure De1. Higher values for f and Q correlate with higher resistance values. The inset in Fig.1(a) (as well as similar insets in Figs 3(a,b) and 5(a)) show the high-ohmic region schematically designated by dark ovals based on the SNMM scan data. The experimental data in Fig.1(c) are presented in variables ξ and η, where ξ = (fEQ - f)/fEQ, η = 0.5(1/Q – 1/QEQ) are the normalized resonance frequency and inverse value of the Q-factor; fEQ, QEQ are parameters f, Q at a contact of probe with etalon EQ. The values A1-A3 in Fig. 1(c) correspond to the three characteristic points on sample De1, indicated in Figs 1(a) and 1(b). The calibration curve ηс(ξ) is plotted from measurements on etalons EQ, ES, E0, E1. The data in Fig.1(c) provide the basis for realizing a method [20] of determining resistance Rsh. Moreover, based on this information we can quickly estimate lateral inhomogeneity of the sample under investigation. In particular, our experience in SNMM measurements prior to the Rsh calculation allows us to assert that sample De1 at points А1, А3 differs in the resistance value by about an order of magnitude. Besides, in the low-ohmic region of the epilayer (vicinity of point А3) we have Rsh > 10 kΩ. Point Ds0 in Fig. 1(c) is for the measurement taken on a dielectric substrate. The location of this point is determined by the real part of the diamond permittivity ε: ε' = Re(ε) = 5.7 (for quartz, sapphire and undoped silicon ε' = 4.5, 10, 11.7, respectively). Diamond substrates often contain macroscopic defects of a crystal structure. Some examples are substrates Ds1, Ds2 whose 3D surface image is shown in Fig.2. In contrast to structures De1, De2, De3 with an epilayer we marked the bare diamond substrates for corresponding samples as Ds1, Ds2, Ds3. The substrate images were taken with an Optical Surface Profiler Zygo NewView 7300. Prior to imaging the surface had been treated by H2/O2 plasma. In Fig. 2 one can see the defective areas of 0.5-1 mm on the substrates. The observed high resistance inhomogeneity in the epilayer of sample De1 (see insert in Fig.1(a)) is, in all probability, related with the structural defect on the substrate Ds1 surface. The latter’s image in Fig.2(а) coincides with the high-ohmic region in the epilayer as measured by SNMM. Results and discussion Based on the SNMM studies it has been established that many of the diamond substrates have a laterally inhomogeneous conductivity. Application of the method [20] to a bulk sample such as substrate, as mentioned above, yields resistivity ρ. Figures 3(a) and 3(b) give the ρ profiles of substrates Ds2 and Ds3. The nonuniform distributions of ρ(x,y) in Fig. 3 – a high-ohmic region with ρ ~10 kΩ cm in the central part, with resistance decreasing towards the edges down to ρ ~ 0.1-1 kΩ cm – are quite typical for 3
substrates under study. The high-ohmic area on substrate Ds2 roughly corresponds to the location of defect, as shown in Fig. 2(b), whereas no macro-defects were observed for Ds3. It should be noted that our VDP-S measurements also revealed appreciable conductivity in a number of substrates. For example, the conductivity of substrate Ds2, obtained by VDP-S technique was ρ = 0.8 kΩ cm. Comparison of this value with the SNMM data in Fig. 3(а) clearly shows that such value of ρ is characteristic only of a substrate edge region. This conclusion is fairly reasonable for objects with inhomogeneous conductivity, since by nonlocal VDP-S measurements a direct current is concentrated in low-resistance areas, which in our case corresponds to the near-edge region of substrate Ds2. In contrast, local SNMM measurements give a distribution ρ(х,у) in the surface plane of a test sample. The developed technique allowed us to obtain scan profiles of resistance Rsh of an epilayer that is grown, in particular, on an inhomogeneously conducting substrate. Distribution ρ(х,у) of the substrate was first measured by the SNMM method (for Ds2 and Ds3, see Fig.3). After growth of the delta-doped epilayer the film-substrate system was scanned by SNMM approximately along the same lines. The effect of the substrate conductivity was taken into account in calculations of the epilayer resistance Rsh by the method [20]. Figure 5 shows the Rsh profiles of the epitaxial film for samples De2 and De3. Scan lines 1 and 3 on sample De3 are interrupted due to the ohmic contacts that had been formed in the corners of the structure for VDP-S measurements. SIMS depth profiles of boron concentration NB(z) in samples De2 and De3 are shown in Figs 4(b) and 4(c), respectively. The effect of substrate conductivity is strongest on SNMM measurements of structures with a highohmic epilayer, such as in sample De3 (see Fig. 5(b)). The average over-all-points value of epilayer resistance is Rsh = 250 kΩ/sq, root-mean-square deviation σR = 100 kΩ/sq. Based on the measured profiles f(x) and Q(x) one could expect a much higher inhomogeneity of epilayer. Corresponding effect was found to be related with the inhomogeneous conductivity of substrate, given a lower resistance of the sample edge area. Indeed, a substrate with 0.3 mm thickness and resistivity ρ = 0.2-11 kΩ cm (see Fig.3(b)) has a dc resistance of 7–370 kΩ/sq. Unlike the dc case, an ac field does not penetrate the entire thickness of the substrate. The depth of a microwave field penetration is determined by a probe aperture size dt and, by our estimation, is about 100 μm. So, the effective shunting resistance of a substrate, arising at SNMM measurements of sample De3 proves to be 20–1000 kΩ/sq depending on a position of the measured point. Considering the above values of Rsh for the epilayer, the low-ohmic part of the substrate largely contributes in the SNMM measured dependences f(x,y), Q(x,y) for the edge area of sample De3. The developed SNMM method yields a resistance value for the epilayer, that is not distorted by substrate. According to the data in Fig.5(b), the epilayer of sample De3 is, apparently, sufficiently homogeneous, and the observed spread in values is most likely related with an error in the SNMM measurements of high-ohmic structures with Rsh > 100 kΩ/sq. By estimates, the limit of Rsh measurement for our SNMM is ~ 500 kΩ/sq, i.e., the Rsh values obtained for De3 are close to the limit. The above estimate of the cutoff value, obtained from the fluctuating sensitivity threshold of our SNMM with respect to parameters f and Q, is suitable for testing a conducting film deposited on any dielectric substrate. At Rsh > 500 kΩ/sq, parameters f and Q measured for the film-substrate system do not differ, within a fluctuation error, from similar parameters for a bare dielectric substrate. For a bulk homogeneous conducting sample, such as the substrates under study here, a similar estimation of cutoff resistivity yields ρс ≈ 15 kΩ cm. At ρ > ρc the SNMM perceives the substrate as a dielectric (point Ds0 in Fig. 1(c)). The limit of measurable characteristics can be increased through a more rigorous temperature/vibration stabilization and other improvements of SNMM. In particular, modern nanometer-resolution devices [6,7] have a higher sensitivity threshold, since they are designed to measure significantly smaller variations of the SNMM resonance curve than mid-resolution microscopes. Naturally, these devices are much more expensive and harder of operation. The measurement capabilities of our SNMM proved fairly adequate to serve the purpose of this work. The findings for sample De2 give evidence of the fact that defects of a substrate crystal structure influence the electrical properties of an epilayer. SNMM scanning results in Fig.5(а) show the inhomogeneity of epilayer resistance Rsh. The high-ohmic region of the layer coincides with the area of structural inhomogeneity on the substrate Ds2 (see inset in Fig.4(b)). Note that in this case the boron concentration profile NB(z), measured by SIMS in three points on the sample both in the defect region and beyond proved to be practically the same (Fig.4(b)). So, a substrate crystal structure defect does not affect 4
impurity content while reducing either a concentration, or mobility of charge carriers in the corresponding region of epilayer. The VDP-S measurement yields resistance Rsh = 8 kΩ/sq, which characterizes only the near-edge area of the epitaxial film and is in accord with the corresponding SNMM data in Fig.5(a), obtained for this region. Rather low resistance values obtained from the edge region of the epitaxial film in sample De2, Rsh ~7-8 kΩ/sq, can be related with a highly doped delta-layer. The fact that SNMM and VDP-S measurements yielded close Rsh results for this region means that the VDP-S data can be used for estimation of electrophysical parameters in it. Taking the delta-layer thickness t = 3.5 nm (see SIMS data in Fig. 4(b)), from the VDP-S data we found the following characteristics for the delta-layer: resistivity ρ = Rsht ≈ 2.510-3 Ω cm, hole concentration Np ≈ 1.71020 cm-3, mobility μH ≈ 15 cm2/(V s). With the peak boron concentration being NB ≈ 3·1020 cm-3 (see Fig. 4(b)), the dopant ionization was estimated at 57%. The obtained characteristics do not contradict the available literature data on conductivity of a delta-layer in diamond [37-43]. However, an unambiguous conclusion that these characteristics pertain to the delta-layer can be made only based on further research, as there may be other conductivity channels in the epilayers of diamond, for example, those arising through addition of electrically active hydrogen on interfaces [44-46]. Thus, SNMM measurements yielded information on epilayer, which is undistorted by the shunting effect and inhomogeneous conductivity of substrate. This allowed us to study electrophysical properties of the epilayer and delta-layer with a higher accuracy. We were also able to correctly use the data from measurements performed by alternative methods. In particular, comparing the photograph of substrate Ds2 in Fig.2(b) with the results of SNMM scanning of sample De2 in Fig.5(a) has led us to a conclusion that the high-ohmic region of epilayer is most likely due to a substrate defect. On the other hand, relating the VDPS measurements data with the low-ohmic near-edge region of sample De2, based on the SNMM results allowed us to a certain degree of reliability estimate the electrical parameters of the delta-layer. The SNMM results are confirmed by the VDP-L measurements. In Table 1 we provide the measured values for the layer resistance Rsh, mobility μH and sheet density Ns of free curriers in structure De3 and its substrate Ds3. The position of crosses I-V is shown in the insets in Figs. 3(b) and 5(b). The obtained values for structure De3 are determined by conductivity of both the epilayer and the substrate. To identify the contributions from either of these two conductivity channels, we measured the substrate resistance after the epitaxial layer had been fully removed. It should be noted that VDP-L measurements on structures with a conducting substrate yield approximate data. The use of the VDP technique requires that ohmic contacts be formed at the edges of a test structure, which was not the case in our VDP-L measurements of samples with a high conductive substrate. The VDP-L studies confirmed the inhomogeneity of conductivity in substrate Ds3. Its high-ohmic region is located in the vicinity of crosses III-V, where measurements failed due to a high resistance between the contacts of the cross. The results Rsh = 60-330 kΩ/sq for sample De3 with an epilayer, that were obtained on crosses III-V, are in agreement with the SNMM data (see Fig. 5(b)), i.e., they refer to the layer. Resistance Rsh = 4-17 kΩ/sq, as well as concentration Ns and mobility μH, measured on crosses I, II, characterize only the substrate that shunts a higher resistance of the epilayer. The same conclusion is made based on the SNMM data given in Figs 3(b) and 5(b). Knowing the substrate thickness and the sheet density Ns, measured using Hall crosses I и II, we can estimate a bulk concentration of free carriers in the substrate conducting area, which is N ~ 1013-1014 1/cm3. The VDP-S resistance measurement on sample De3 with an epilayer yields Rsh = 20 kΩ/sq, which is conditioned by the low-ohmic edge region of the substrate. So we see that non-local VDP studies of an epilayer in substrates with inhomogeneous conductivity may not be informative enough. SNMM measurements in the same conditions yield objective information on a layer resistance.
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TABLE 1. VDP-L measurements of electrical parameters for sample De3 and substrate Ds3. μH, cm2/(V s) Ns, 1/cm2 Number of cross Rsh, kΩ/sq (sample/substrate) (sample) (sample) I 17/17 1180 3.2×1011 II 5/4 680 1.5×1012 III 130/18 2.8×1012 IV 330/– – V 60/31 3.4×1012 Results of the VDP-L resistance measurements on sample De2 are presented in Table 2. The position of Hall crosses I-V is shown in the inset in Fig.5(а). The conclusions made from the SNMM studies were also found to be true for sample De2: maximum resistance is observed at crosses II, III over the defect region of substrate; outside this region (crosses I, IV) the epitaxial layer resistance is decreasing. The obtained SNMM and VDP-L values of Rsh show a mutually satisfactory agreement (compare Fig. 5(a) with the data in Table 2). The only exception is point III at which the difference in the measurement result by an order of magnitude is apparently connected with an error in the SNMM and VDP-L techniques when measuring high values of resistance Rsh. TABLE 2. VDP-L measurements of Rsh for sample De2. Number of cross Rsh, kΩ/sq I 54 II 310 III 4500 IV 47 V Cross damaged Conclusion In this paper it has been demonstrated that the developed SNMM technique is an effective tool for quantitative characterization of semiconductor doped structures. Major advantages of our mid-resolution SNMM include local and nondestructive non-contact diagnostics that show up most vividly in the process of developing the technologies for new materials fabrication. One example of such material is semiconductor diamond. We have studied boron delta-doped CVD diamond structures epitaxially grown on an HPHT substrate. Working out a technology for doping and characterization of diamond structures involves great difficulties related, in particular, with small sizes, macroscopic defects and laterally inhomogeneous conductivity of substrates. Thus, the VDP-S method proved to be least informative in the case when the substrate shunted the doped epilayer due to high conductivity in the edge region. VDP-L measurements allowed us to obtain local data only at some points in the central part of a sample surface, provided that the epilayer on the rest of the substrate surface had to be removed. The SIMS technique yielded high homogeneity of the doping impurity concentration, when the conducting properties of a structure were strongly inhomogeneous. In these conditions, when characterization of diamond samples proved to be rather complicated, the SNMM merits showed up most vividly. Our SNMM method enabled mapping of resistance Rsh of a delta-doped epilayer of diamond grown on a defective substrate with an inhomogeneous conductivity. One of the primary claims of this work is that the SNMM method enables spatially-resolved characterization of sheet resistance of an epilayer, when the supporting substrate has shunting and inhomogeneous conductivity. With the method [20] (when only one unknown parameter of a test structure is to be determined) such testing was possible only by independent scanning of a bare substrate and a substrate with the grown epilayer. However, the SNMM technique has a potential for solving more complicated inverse problems of testing structures with a few parameters being measured simultaneously. Diagnostics of multiparametric objects involves complex measurements, for example, over some frequency 6
ranges or using a number of probes differing in aperture size. A possibility of solving such problems with SNMM was demonstrated in Ref. [47] through computer modeling. Acknowledgments The authors are grateful to colleagues from laboratory of Prof. A.L.Vikharev (Institute of Applied Physics RAS, N.Novgorod, Russia) for fabricating the diamond structures, and to Prof. V.I. Shashkin (Institute for Physics of Microstructures RAS, N. Novgorod, Russia) for organization and technology provision of VDP-L measurements. We also thank the above-mentioned colleagues and Prof. D.E.Butler (Institute of Applied Physics RAS, N. Novgorod, Russia) for useful discussions. This work was supported by RFBR under Grant N 15-02-04081 and by the Program of the Department of Physical Sciences RAS. This research was based on the equipment of the Common Research Center “Physics and technology of micro- and nanostructures” at the Institute for Physics of Microstructures RAS.
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Figure captions Fig.1. (a) Resonance frequency f and (b) Q-factor obtained by SNMM scanning of sample De1 along lines 1-3. (c) Parameters f , Q in normalized variables ξ, η. А1-А3 – the values for ξ, η in points on the surface of sample De1, marked in Figs (a) and (b). Line is calibration curve с(), calculated from measurements on etalons EQ, ES, E0, E1. Point Ds0 – measurement on dielectric diamond substrate. The inset in Fig. (a) shows scanning lines 1-3 and approximate location of high-ohmic region (dark ovals). Fig.2. Surface image of substrates (a) Ds1 and (b) Ds2. 1-3 – SNMM scan lines, ovals – the high-ohmic region. Arrow indicates the defect location. Fig.3. Resistivity profiles for substrates (a) Ds2 and (b) Ds3, scanned along lines 1-3. The insets show scanning lines 1-3 and approximate location of high-ohmic regions (dark ovals). The inset in Fig. (b) also shows the position of Hall crosses. Fig.4. Depth profiles of boron atoms concentration NB(z) for samples (a) De1, (b) De2 and (c) De3. The inset in Fig. (b) shows points 1-3 on the surface of sample De2, at which we obtained profiles NB(z). Fig.5. Scan profiles of the epilayer resistance for samples (а) De2 and (b) De3. Right-hand insets of Figs (a) and (b) show scanning lines 1-3 and position of crosses I-V under VDP-L measurements. In the right-hand inset of Fig. (a) the dark oval indicates a high-ohmic region. The left-hand inset of Fig. (a) shows a Hall cross structure.
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