D.B. Radishev, A.L. Vikharev, A.M. Gorbachev, A.B. Muchnikov, P.A. Yunin, V.N. Amosov, N.B. Rodionov 1 Institute of Applied Physics of the Russian Academy of Sciences, Nizhny Novgorod, Russia 2 Institute for Physics of Microstructures of the Russian Academy of Sciences, Nizhny Novgorod, Russia 3 Russian State Research Center, Troitsk Institute for Innovation and Fusion Research, Troitsk, Moscow, Russia

Обсуждаются способы экспериментальной диагностики и управления величиной отклонения плоскости поверхности монокристаллических алмазных HPHT (High Pressure High Temperature) пластин относительно кристаллографических плоскостей (001). Такие пластины (подложки) используются для гомоэпитаксиального выращивания как легированных, так и нелегированных пленок CVD алмаза. При травлении HPHT подложек в плазме СВЧ разряда в чистом водороде либо в водород-кислородной смеси наблюдается формирование сингулярных террас с ориентацией поверхности (001). Это явление может быть использовано как для экспресс-анализа ориентации подложки и повышения точности контроля угла отклонения при шлифовке подложек, так и для получения макроскопических сингулярных (001) участков монокристаллических алмазных подложек.

Detailed description of a way to accrete diamond single crystals in one plate using the CVD method is presented. It was found that each region of the mosaic CVD diamond crystal grown over a certain seed substrate “inherits” the crystallographic orientation of its substrate. No correlation was found between the value of misorientation of the accreted crystals and entrance of hydrogen to the boundary. It is shown that successful accretion of single crystal diamond plates in a single mosaic crystal occurs even in the case of great misorientation of crystals. The mechanical stresses appear during the fabrication of the mosaic CVD diamond crystal. Stresses accumulate during accretion of the regions, which grow over substrates with different orientations, in a common structure.

Приведены результаты анализа атомного состава, уровня легирования и подвижности дырок в эпитаксиальных слоях CVD (chemical vapor deposition) алмаза при легировании бором. Показаны возможности однородного легирования бором в диапазоне от 5·1017 до ~1020 ат/см3 и delta-легирования с поверхностной концентрацией (0.3-5)·1013 ат/см2. Определены режимы прецизионного ионного травления структур, сформированы барьерные и омические контакты к слоям.

We report on building a novel chemical vapor deposition (CVD) reactor for diamond delta-doping. The main features of our reactor are: a) the use of rapid gas switching system, (b) the reactor design providing the laminar gas flow. These features provide the creation of ultra-sharp interfaces between doped and undoped material and minimize the prolonged "tails" formation in the doping profile. It is proved by optical emission spectroscopy that gas switching time is not more than 10 seconds. Using the novel reactor we have grown the nanometer-thin layers of boron doped diamond. The FWHM of boron concentration profile is about 2 nm which is proved by SIMS. It is shown that the both single delta-layer and multiple delta-layers could be grown using the novel CVD reactor. In principle, the reactor could be used for diamond delta doping with other dopants, like nitrogen, phosphorus etc. (C) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Methods of the experimental diagnostics and control of the misorientation angle for single-crystal HPHT (High Pressure High Temperature) diamond substrates are discussed. Such substrates are used for the homoepitaxial growth of doped and undoped CVD diamond layers. The formation of singular (001) terraces on the surface of HPHT diamond after microwave-discharge-plasma etching in pure hydrogen or a hydrogen–oxygen mixture is observed. This phenomenon can be used for rapid determination of the substrate misorientation and to improve the control precision of the deviation angle during substrate polishing, or for obtaining large singular (001) areas of single-crystal diamond substrates.

The name of the last author should read J. E. Batler.

Diamond is desired for active semiconducting device because of it high carrier mobility, high voltage breakdown resistance, and high thermal diffusivity. Exploiting diamond as a semiconductor is hampered by the lack of shallow dopants to create sufficient electronic carriers at room temperature. In this work, nanometer thick, heavily boron doped epitaxial diamond ‘delta doped’ layers have been grown on ultra smooth diamond surfaces which demonstrate p type conduction with enhanced Hall mobilities of up to 120 cm2/Vs and sheet carrier concentrations to 6 × 1013 cm–2, thus enabling a new class of active diamond electronic devices. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)

The study of combined single-crystalline and polycrystalline chemical vapor deposited (CVD) diamond wafers is reported. Combined CVD diamond wafers up to 75 mm in diameter were grown, which consist of great number of single-crystalline diamond sections grafted in a polycrystalline diamond matrix. The grown combined CVD wafers were characterized by the Raman spectroscopy. It was shown that in the grafting process, the single- and polycrystalline areas of the combined wafer undergo insignificant stresses, which can be released during the thermal annealing process. Fabricated combined CVD diamond can be used in various applications that employ unique properties of diamond and potentially suitable for industrial use.

Original approach to fabricating a GaN/AlN/nanocrystalline diamond structure has been suggested and implemented. The stages of deposition of a structure of this kind include the following: (a) growth of nanocrystalline CVD-diamond on single-crystal AlN (preliminarily grown on a silicon substrate), (b) etch removal of the silicon substrate, and (c) growth of single-crystal GaN on the surface of single-crystal AlN. Single-crystal gallium nitride with a width of the X-ray rocking curve for the (0002) reflection of 0.35° was obtained on a nanocrystalline-diamond substrate.

The surface morphology of vicinal (100) single‐crystal diamond surfaces homoepitaxially grown in a microwave plasma‐assisted chemical vapor deposition (MPACVD) reactor is studied. High‐pressure and high‐temperature (HPHT) single‐crystal diamond substrates produced by different vendors are used as substrates. Prior to the CVD growth, substrates were mechanically polished and etched in a separate inductively coupled plasma/reactive ion etching (ICP/RIE) tool using an Ar/Cl2 gas mixture. The impact of (a) ICP etching regime of the HPHT substrate, (b) substrate polishing, and (c) the HPHT substrate misorientation (off‐axis) vicinal angle on the surface morphology is examined. It was found that the ICP etching removes polishing‐induced defects in the bulk and also removes diamond particles which are left on the surface of single‐crystalline diamond after polishing. The morphology of the surface of the homoepitaxial CVD diamond grown on a substrate, which is free of polishing defects, depends not only on the parameters of the growth process (substrate temperature, composition of the gas mixture, pressure, etc.), but also on the value and direction of the off‐axis angle.

Hydrogen plasma etching of (1 0 0) surfaces of single crystal diamonds were investigated. Etching rates, surface morphology of the etched diamond samples and shape of etch-pits were analyzed. These experiments demonstrated that the etching rate increases exponentially with increasing substrate temperature, strongly depends on crystal surface orientation and increases with an increasing vicinal angle. The activation energy for the etching process on (1 0 0) diamond was determined (Ea=45.4±4.5 kcal/mol). Hydrogen plasma etching could be used for revealing substrate defects and preparing substrate surface prior to CVD growth.

The effect of nitrogen addition on the growth rate, quality, and properties of polycrystalline diamond grown by microwave plasma assisted (MPA)CVD is investigated. Two series of experiments are performed at two different microwave power densities (40 and 110W cm(-3)) using a 2.45 GHz cylindrical microwave reactor. The results show that the beneficial effect of nitrogen is more distinct at higher microwave power densities. To investigate the properties of polycrystalline diamond grown with nitrogen addition, a thick diamond disk of 50mm diameter is grown with an addition of 50ppm nitrogen using a 2.45 GHz ellipsoidal microwave reactor. The grown diamond disk has a thermal conductivity of 17.3W cm(-1) K-1 and dielectric loss tangent of 3.7x10(-5) at a frequency of 170 GHz, and its parameters are suitable for application in microwave windows (e.g., gyrotron windows). Our results indicate that it is possible to achieve the increased (by a factor of 2.5) growth rates by nitrogen addition without significant degradation of diamond quality, and properties such as thermal conductivity and dielectric loss tangent.The effect of nitrogen addition on the MPACVD synthesis of polycrystalline diamond is investigated with the aim of growth-rate enhancement of high-quality, low-loss CVD-produced diamond disks. Experiments are performed at microwave power densities of 40 and 110 W cm(-3) using a 2.45 GHz microwave reactor. The amount of added nitrogen needed to grow CVD disks of high quality (suitable for application in microwave windows) 2.5 times faster compared with the nitrogen-free synthesis, is determined.

The study of combined single-crystalline and polycrystalline chemical vapor deposited (CVD) diamond wafers is reported. Combined CVD diamond wafers up to 75mm in diameter were grown, which consist of great number of single-crystalline diamond sections grafted in a polycrystalline diamond matrix. We used the thermal annealing process to release insignificant stresses which originate during the grafting process between the single- and polycrystalline areas of the combined wafer. Fabricated combined CVD diamond can be used in various applications that employ unique properties of diamond and potentially suitable for industrial use.

The fabrication of diamond substrates in which single-crystalline and polycrystalline CVD diamond form a single wafer, and the epitaxial growth of diamond films on such combined substrates containing polycrystalline and (100) single-crystalline CVD diamond regions are studied.

The parameters of a pulsed microwave discharge in a 2.45 GHz chemical vapour deposition (CVD) reactor used for diamond growth are studied. It is shown that the use of the pulsed-wave mode allows one to increase the growth rate of polycrystalline diamond films by 2–3 times without deterioration of their quality for a fixed mean microwave power and a specified deposition area. An optimal pulse repetition rate is found, at which both the growth rate and the diamond film quality are higher than at the other repetition rates (for an equal mean power). We explain this effect by the increase in the near-surface atomic hydrogen density. The optimal pulse repetition rate value depends on the growth parameters (reactor geometry, gas pressure and power density), and on the growth substrate size. For the substrates 20–40 mm in diameter (and the CVD reactor used in the study), the optimal pulse repetition rate is 250 Hz. The method of graphite sample etching in hydrogen plasmas was used to measure the atomic hydrogen near-surface density. This method can be applied to the optimization of diamond film growth in CVD reactors of different types. Additionally, it can be used to compare different CVD reactors by determining the yield of atomic hydrogen. It is shown that at an equal mean power absorbed in the discharge, the maximum gas temperature during the microwave pulse increases, as the pulse repetition rate decreases. This behaviour of gas temperature can explain the similar dependence of the period-averaged intensity of the C2 radical optical emission (516.5 nm) on the pulse repetition rate.

The homoepitaxial single crystal diamond growth by microwave plasma assisted CVD at high microwave power density 200W/cm3 in a 2.45GHz MPACVD reactor using natural diamond seeds (type IIa) was investigated. The semiconductor CVD diamond of p-type was obtained by doping technique of ion implantation. Boron ions were implanted at the acceleration energy of 80keV with two cases of dose: 5·1014 and 3·1015cm−2. To recover the damage layer and activate dopants in CVD diamond the rapid annealing at nitrogen atmosphere at 1380°C was used. B-implanted diamond layer showing the mobility of 1150cm2/Vs at 300K which is the highest for ion-implanted diamond was obtained.

The results of studies of single-crystal diamond layers with orientation (100) grown on substrates of IIa-type natural diamond by chemical-vapor deposition and of semiconductor diamond obtained subsequently by doping by implantation of boron ions are reported. Optimal conditions of postimplantation annealing of diamond that provide the hole mobility of 1150 cm 2 V −1 s −1 (the highest mobility obtained so far for semiconductor diamond after ion implantation) are given.

Homoepitaxial growth of single crystal diamond by microwave plasma chemical vapor deposition in pulsed regime of a 2.45 GHz MPACVD reactor operation at pulse repetition rates of 150 and 250 Hz was investigated. The high quality CVD diamond layers were deposited in the H-2-CH4 gas mixture containing 4% and 8% of methane, gas pressures of 250 and 260 Torr and substrate temperature of 900 degrees C without any nitrogen addition. The (100) HPHT single crystal diamond seeds 2.5 x 2.5 x 0.3 mm (type Ib) were used as substrates. At pulse repetition rate 150 Hz the high quality single crystal diamond was grown with growth rate of 22 mu m/h. The comparison of the single crystal diamond growth rates in CW and pulsed wave regimes of MPACVD reactor operation at microwave power density 200 W/cm(3) was made. It was found that at equal power density, the growth rate in pulsed wave regime was higher than in CW regime. Differences in single crystal diamond growth for two sets of experiments (with continuous and pulsed wave regimes) were explained. (C) 2011 Elsevier B.V. All rights reserved.

Homoepitaxial growth of single crystal diamond by microwave plasma chemical vapor deposition in a 2.45GHz reactor was investigated at high microwave power density varied from 80W/cm3 to 200W/cm3. Two methods of achieving high microwave power densities were used (1) working at relatively high gas pressures without local increase of electric field and (2) using local increase of electric field by changing the reactor geometry (substrate holder configuration) at moderate gas pressures. The CVD diamond layers with thickness of 100–300µm were deposited in H2–CH4 gas mixture varying methane concentration, gas pressure and substrate temperature. The (100) HPHT single crystal diamond seeds 2.5×2.5×0.3mm (type Ib) were used as substrates. The high microwave power density conditions allowed the achievement of the growth rate of high quality single crystal diamond up to 20µm/h. Differences in single crystal diamond growth at the same microwave power density 200W/cm3 for two process conditions—gas pressure 210Torr (flat holder) and 145Torr (trapezoid holder)—were studied. For understanding of growth process measurements of the gas temperature and the concentration of atomic hydrogen in plasma were made.