Plasma physics and high-power electronics division

Diamond Electronics Laboratory


The results of the first phase of the project:

A reactor to produce delta layer of boron-doped CVD diamond is designed, it will provide the epitaxial growth of both single-crystal diamond layers of electronic quality (low level of impurities) and controlled growth of delta layers doped with boron.
For obtaining of the epitaxial layers of electronic quality CVD diamond, the characteristics (quality of the crystal lattice defects and impurities) for diamond substrates produced by the high-pressure high-temperature technology were studied by methods of Raman spectroscopy and photoluminescence, optical, scanning electron and scanning probe microscopy, white light interferometry, SIMS (secondary ion mass spectrometry).
The analysis of the promising types of microwave devices, electronics, power electronic devices and Schottky diodes based on CVD diamond were made. Different versions of their designs were considered.
Different methods of fabrication of electronic devices based on single-crystal diamond - the formation of contacts, lithography, etching – were tested.

Publications on the project:

S.A. Bogdanov, A.L. Vikharev, A.M. Gorbachev, A.B. Muchnikov, D.B. Radishev, N.M. Ovechkin and V.V. Parshin, Growth rate enhancement of high quality low-loss CVD diamond disks grown for microwave windows application, Chemical Vapour Deposition, Volume 20, Issue 1-2-3,  pages 32–38, March 2014,

The results of the second phase of the project:

A microwave plasma CVD reactor for growing layers of boron delta-doped CVD diamond was built and tested. A separate microwave plasma CVD reactor operating at 2.45 GHz  was used for the epitaxial deposition of single crystal CVD diamond of high quality with nitrogen content in the sample of less than 100 ppb. Such level of nitrogen impurity corresponds to the electronic grade diamond.

Uniformly boron doped CVD diamond layers with a thickness of 2-2.5 um were also grown.  The concentration of boron in the grown diamond samples was in the range 1018 -1020 cm-3. A method for monitoring the level of doping during the growth process of CVD diamond using optical emission spectroscopy of the discharge was developed.

Methods of mechanical polishing of a single crystal HPHT diamond substrates for subsequent diamond homoepitaxial growth of CVD diamond was developed and tested. A series of substrates of (100) oriented HPHT diamond with size of (3,5x3,5x0,5 mm3), with roughness of less than 2? and misorientation angle of not more than 0,1o were prepared. An ICP-RIE etching process of single crystal substrates in an Ar/Cl2 plasma at low pressure (dry etching in an inductively coupled plasma combined with reactive ion etching) for removal of the surface layer of single-crystal diamond substrate damaged during polishing was studied in detail. Etching process of (100) diamond substrates was investigated.

The technology for growing of large-area composite CVD wafers (diameter up to 76 mm) containing more than 100 single-crystal CVD diamonds grown into polycrystalline diamond base was developed. The technology developed includes a junction of poly- and monocrystalline areas during the process of the CVD growth, the removal of mechanical stresses between areas by high-temperature annealing, and the growth of boron-doped epitaxial CVD layers on single-crystal areas of composite wafer. An application of this technology allows one to obtain a combined wafer suitable for creation of electronic devices based on semiconductor CVD diamond using existing manufacturing lines.

New design of a delta-doped conductive channel field-effect transistor based on the use of the new profile of boron concentration distribution in the channel having two closely placed (at a distance of about 3 nm) peaks was proposed and justified by calculations. It was shown that such a doping profile provides increase of mobility and hence increase of channel conductivity by 60% compared with a profile with a single peak.

The simulation of the field effect transistor in which the conducting channel is created using the hydrogen-rich surface layer was made. At the value of the surface charge of 1013 cm-2, the following characteristics of the transistor was obtained: slope of 250 mSim/mm, cut-off frequency 25-30 GHz, frequency of maximum power gain 90-100GHz. It was shown that the voltages and currents in the proposed variant of the transistor is almost an order of magnitude higher than the operating voltages and currents of HEMT transistor with the same geometry.

The simulation of a m-i-p structure Schottky diode was made. The technology of manufacturing of Schottky diodes on the base of semiconductor CVD diamond using the Pt contacts deposited by photolithography was developed. Experimental samples of Schottky diodes using the boron-doped layers of CVD diamond were manufactured and their current-voltage characteristics were examined. The current-voltage and capacitance-voltage characteristics of obtained structures were studied. It was shown that the capacitance-voltage measurements of semiconductor CVD diamond is characterized by a significant deviation from the principle of quasi-static measurement (independence on the test signal frequency). Basing on results of the capacitance-voltage measurements the concentration of main charge carriers (holes) at different temperatures was estimated.

Publications on the project:

A.B. Muchnikov, A.L. Vikharev, D.B. Radishev, V.A. Isaev, O.A. Ivanov, A.M. Gorbachev,  A wafer of combined single-crystalline and polycrystalline CVD diamond, Materials Letters, 2015, 139, pp.1-3;

Kukushkin V.A., Snider G.L., Bogdanov S.A., Chernov V.V., Delta layer doping profile in diamond providing high carrier mobility, physica status solidi RRL, Volume 8, Issue 10, pp 876-879,

Кукушкин В. А., Увеличение радиационного времени жизни экситонов Ванье−Мотта в полупроводниковых нанокластерах, Физика и техника полупроводников, Tом 49, вып.1,

S.P. Antipov, S.V. Baryshev, J.E. Butler, C. Jing, A.D. Kanareykin, P. Schoessow, M. Conde, W. Gai, J.G. Power, S. Stoupin, RF breakdown test of diamond-loaded resonator for high gradient wakefield accelerator applications, Diamond & Related Materials,

Bogatskiy A., James E. Butler, A Geometric Model of Growth for Cubic Crystals:  Diamond, Diamond and Related Materials, 53 (2015), 58-65,

Vikharev A.L., Muchnikov A.B., Radishev D,B., Isaev V.A., Ivanov O.A., Gorbachev A.M., Growth and characterization of combined single-crystalline and polycrystalline CVD diamond wafer, MRS Online Proceedings Library, 2014, v.1734, mrsf14-1734-r09-01,

Ivanov O.A., Muchnikov A.B., Chernov V.V., Bogdanov S.A., Vikharev A.L., Butler J.E., Experimental study of hydrogen plasma etching of (100) single crystal diamond in a MPACVD reactor, Material Letters,

The results of the third phase of the project:

Uniformly boron doped CVD diamond layer with a thickness of 2-2.5 um were produced, the concentration of boron was in the range 1018-1019 cm-3. It was shown that the control of the hydrogen flow through a solution of trimethylborate in ethanol, and adjusting the concentration of trimethylborate allows extending the range of boron doping level of diamond to 1016 to 1021 cm-3. Electrophysical characteristics of boron-doped CVD diamond layer have been investigated by X-ray topography and diffractometry, FT-IR spectroscopy, cathodoluminescence.

As a result of the measurement with a method of admittance spectroscopy the IV and CV characteristics of experimental samples of highly boron-doped diamond single-crystal layers were determined. The dependence of the activation energy of the boron impurities on the degree of doping was determined. A transition to the hopping conductivity type at high concentrations of boron was found.

The ICP-RIE etching process of single crystal substrates in Ar/Cl2 plasma at low pressure was studied in detail. It was shown that the ICP-RIE method is promising for homogeneous (over the entire area of the sample) removal of the surface layer of single-crystal diamond substrate which was damaged in the process of polishing. It was found that the method of etching does not deteriorate the surface roughness achieved during mechanical polishing. It is shown that during the epitaxial growth of single crystal CVD diamond on HPHT substrates structural defects may occur, which are induced by the process of grinding and/or polishing, but not with the characteristics of the deposition regime and/or presence of dislocations in the substrate. It was found that with the etching of substrates in the ICP-RIE plasma, the increase of the etching depth decreases the density of grinding defects up to their complete disappearance.

Homoepitaxial CVD diamond single crystal layers of high quality were grown. Single crystal diamond layers were obtained with a thickness of about 1 mm and higher quality than that of the HPHT diamond substrate.

A setup for study of the diamond by method of "micro-Raman" spectroscopy was made. The apparatus allows measuring Raman and photoluminescence spectra with high spatial resolution (spot size about 1 micron), and provides information about the crystalline perfection of the diamond phase (the width of the peak corresponding to the diamond), and the presence of non-diamond phases (graphite, amorphous carbon), defects and impurities, such as (NV)0, (NV)- and "silicon-vacancy" (Si-V) complexes.

An experimental set of samples with epitaxial layers of CVD diamond were studied by micro-Raman spectroscopy. It was found that the full width at half maximum of the Raman peak corresponding to the diamond is about 1.7 cm-1 on the entire surface of the sample, which indicates a high crystalline perfection of the samples. Measurements showed that the nitrogen content in the samples is only a few ppb.

A fundamentally new type of reactor for growth of boron-doped delta layer CVD diamond was created. For this reactor a special system for supplying gas was developed, providing simultaneous feeding of a gas mixture consisting of six different gases to the reactor and fast switching to another composition of the gas mixture, and having laminar flow of gases in the reaction chamber. Highly boron doped diamond delta-layers with thickness of 2-3 nm were produced in this reactor.

The design and modeling of different devices based on diamond was performed. Modeling of insulated gate p-i-p transistor at different thicknesses of heavily doped layer (200 nm and 50 nm) showed the possibility of obtaining the following characteristics of the device: characteristic slope of about 150-200mSim/mm, cut-off frequency of 20 GHz, frequency of maximum power gain of 80 GHz. This transistor, when compared to a HEMT transistor with the close geometrical sizes, features an order of magnitude higher voltages and currents.

The technology of micro-profiling of diamond substrate by RIPT (reactive ion plasma etching) was developed. It was shown that the method of forming the metal masks allows obtaining high selectivity of the diamond etching. Test mesa-structures with vertical walls and low defects were obtained.

Studies were made on developing the technology of applying Pt – as a metal, that the Pt-diamond structure forms a Schottky barrier with a highest value compared with the technologically available metals, such as: Ni, Ta, W, Ti, Al, V. Platinum was deposited by sputtering on the substrate without the epitaxial layers. It was shown that this technology allows forming a contact of Pt-C with necessary topology by lift-off method and ensures good adhesion of metal to the diamond.

A method for surface passivation of device structures using Al2O3 deposition was proposed to reduce surface leakage current in planar Schottky diodes. The technology of applying the protective insulating layer of Al2O3 (70 nm thick) by atomic layer deposition was developed. The study of obtained Al2O33 films by ellipsometry and electron microscopy showed their high quality and uniformity of deposition.

Contactless method for non-destructive measurements of the microwave characteristics of experimental samples of devices fabricated using delta-doped diamond layers was designed. The basis of this method is the measurement of S-parameters of developed measuring cell and the subsequent calculation of complex permittivity and permeability of the structure in accordance with Nicholson-Ross algorithm. Due to the close relation between the complex permittivity and conductivity of the delta-doped layer, concentration of charge carriers collected in the delta layer is estimated. The simulation of three different designs of the measuring cell was made, optimum cell design based on symmetric microstrip transmission line was selected and produced.

Publications on the project:

M.A. Lobaev, S.A. Bogdanov, D.B. Radishev, A.L. Vikharev, A.M. Gorbachev, Method of power density determination in microwave discharge, sustained in hydrogen-methane gas mixture, Diamond & Related Materials 66 (2016) 177-182, 

A.B. Muchnikov, D.B. Radishev, A.L. Vikharev, A.M. Gorbachev, A.V. Mitenkin, M.N. Drozdov, Yu.N. Drozdov, P.A. Yunin, Characterization of interfaces in mosaic CVD diamond crystal, Journal of Crystal Growth, 442 (2016) 62–67,

A. L. Vikharev, A. M. Gorbachev, M. A. Lobaev, A. B. Muchnikov, D. B. Radishev, V. A. Isaev, V. V. Chernov, S. A. Bogdanov, M. N. Drozdov, and J. E. Butler, Novel microwave plasma-assisted CVD reactor for diamond delta doping, Phys. Status Solidi RRL, 1–4 (2016),

V.A. Kukushkin, S.A. Bogdanov, Simulation of CVD diamond-based high speed near-infrared photodetectors, Diamond & Related Materials 60 (2015) 94–98,

V. I. Zubkov, O. V. Kucherova, S. A. Bogdanov, A. V. Zubkova, J. E. Butler, V. A. Ilyin, A. V. Afanas'ev, A. L. Vikharev, Temperature admittance spectroscopy of boron doped chemical vapor deposition diamond, Journal of Applied Physics 118, 145703 (2015);

O. A. Ivanov, A. M. Gorbachev, A. L. Vikharev, M. A. Lobaev, V. A. Isaev, V. V. Chernov, Electron emission amplification of cold cathode by two-layer diamond coating, Phys. Status Solidi A, 212: 1779–1784.

O.A.Ivanov, A.B.Muchnikov, V.V.Chernov, S.A.Bogdanov, A.L.Vikharev, J.E.Butler, Experimental study of hydrogen plasma etching of (100) single crystal diamond in a MPACVD reactor, Materials Letters, 151 (2015) 115–118,

A. B. Muchnikov, A. L. Vikharev, J. E. Butler, V. V. Chernov, V.A. Isaev, S.A. Bogdanov, A. I. Okhapkin, P. A. Yunin, and Y. N. Drozdov, Homoepitaxial growth of CVD diamond after ICP pretreatment, Phys. Status Solidi A, 212: 2572–2577.

О.И. Хрыкин, Ю.Н. Дроздов, М.Н. Дроздов, П.А. Юнин, В.И. Шашкин, С.А. Богданов, А.Б. Мучников, А.Л. Вихарев, Д.Б. Радищев, Монокристаллические слои GaN/AlN на CVD-алмазе, Письма в ЖТФ, 2015, том 41, вып. 19, c.8-15

М.А. Лобаев, О.А. Иванов, А.Л Вихарев, А.М. Горбачев, В.А. Исаев, Исследование взаимодействия пучка электронов с сильным высокочастотным полем в волноводном переключателе мощного СВЧ компрессора, Изв. Вузов. Радиофизика, т.58, №.11, c.913-922, (2015)

A.L.Vikharev, A.B.Muchnikov, D.B.Radishev, V.A.Isaev, O.A.Ivanov, A.M. Gorbachev, Growth and characterization of combined single-crystalline and polycrystalline CVD diamond wafer, Pittsburgh, PA, MRS Proceedings, V.1734, (2015),

Диагностика эффективности возбуждения поверхностных плазмон-поляритонов квантовыми точками с помощью поляризационных измерений выходного излучения, Кукушкин В.А., Физика и техника полупроводников, 2015, том 49, вып 6

O.A. Ivanov, A.L. Vikharev, A.M. Gorbachev, Experimental study of plasma decay in pulsed microwave discharges of H2, CH4 and their mixtures, Plasma sources, science and technology, v.25, N3, 2016

M.A. Lobaev, S.A. Bogdanov, D.B. Radishev, A.L. Vikharev, A.M. Gorbachev, Investigation of microwave discharge in cavity reactor excited in the TM013 mode, Proceedings of IX International workshop “Microwave discharges: fundamentals and applications”, September 7-11, 2015, Cordoba (Spain), pp.83-88

Зубков Василий Иванович, Панов Михаил Федорович, Афанасьев Алексей Валентинович, Ильин Владимир Алексеевич, Ламкин Иван Анатольевич, Батлер Джеймс Эхрич, Вихарев Анатолий Леонтьевич, Богданов Сергей Александрович, На пути к дельта-легированному полупроводниковому алмазу, Нано- и микросистемная техника, 2015, Декабрь, № 12 (185)

Витько Виталий Валерьевич, Кондрашов Александр Викторович, Никитин Андрей Александрович, Батлер Джеймс Эхрич, Измерительная ячейка для исследования СВЧ-свойств дельта-легированных алмазных образцов, Известия вузов России: Радиоэлектроника, 2015, 3

Вихарев А.Л., Лучинин В.В., CVD алмаз – материал для нового поколения электронных приборов: выращивание, характеристики и некоторые применения, Электроника и микроэлектроника СВЧ, 2015. Т. 1. № 1. С. 29-33.

С.А. Богданов, А.Л. Вихарев, М.Н. Дроздов, Исследование синтеза полупроводникового CVD алмаза при высокой степени легирования, Электроника и микроэлектроника СВЧ, 2016. Т. 1. № 1. С. 79-81.

The results of the 4th phase of the project:

The following results were obtained during the implementation of the fourth stage of project.
The conditions for obtaining of high-quality, high-purity single crystal epitaxial CVD diamond surrounding the delta-doped layer were studied. Quality of the diamond was determined depending on the methane content in the working gas mixture and the diamond substrate misorientation angle (angle between the normal to the surface of the diamond substrate and the crystallographic direction [001]). As a result the growth rate of epitaxial layers and the optimal misorientation angle to obtain high-quality layers were determined.
The efficiency of boron incorporation in the single crystal diamond depending on the CVD diamond deposition conditions was investigated. The optimum range of the substrate temperature and the concentration ratio of boron to carbon in the gas mixture at which incorporation of boron into the diamond lattice reaches maximum were determined.
Experimental samples of delta doped diamond layers were manufactured, delta layers with thickness as low as 1.4-2.5 nm and high concentration of boron (3-9)×1020 cm-3 were obtained.
Using the results of experimental samples measurements by the Van der Pauw method, value of the maximum hole mobility of 300 V2/cm×s was determined. In experiment the separation of holes and boron doping atoms is clearly manifested, so the hole mobility includes integrated value of different areas of the diamond - doped with low mobility and non-doped with high mobility. This is confirmed by the study of dependence of the mobility and the holes concentration on the temperature. Thus, for the first time the effect of increase of the holes mobility due to the holes separation from the doping boron atoms was observed in the epitaxial diamond delta-layers. This proves the high quality of manufactured structures - the sharpness of doping profile transitions, high-quality of undoped epitaxial layers and a high concentration of boron in the delta layer.
Using the methods of lithography and precision etching of diamond in oxygen plasma the test mesa structure with vertical current flow was formed for C-V measurement of the holes profile in the CVD diamond with delta-layers. Profile of the holes concentration was measured using test structure and its temperature dependence in the temperature range 260 - 400K was determined. For the investigated boron delta layer in the diamond the activation energy was defined to be about 60 meV, which is considerably less than the activation energy of boron in the diamond (370 meV) and corresponds to a high concentration of boron, which according to the SIMS exceeds 3×1020 cm-3.
Numerical modeling of structures with multiple delta-doped layers was made with consideration of quantum-mechanical effects. It was found that two or more layers in the delta-CVD-diamond structure can increase the concentration of impurities and therefore carriers in the channel of the FET. The optimization of delta-layers position can provide higher charge carrier mobility.
By method of numerical simulation the optimization of the position of boron-doped delta layer relative to the surface of the epitaxial layer to achieve the maximum performance characteristics of the FET was made.
Plasma etching of the diamond was studied in various gas mixtures containing chlorine, sulfur hexafluoride, oxygen with argon or helium as buffer gas. Regimes were defined in which there occurs no development of etched surface roughness, etching rate of various materials and their selectivity to the diamond were compared. Thus, technology of etching of epitaxial layers of CVD diamond to the ultra-low depth in order to open the windows to the delta-doped layer was tested.
The technology of producing of low-resistance ohmic contacts to the diamond films with p-type conductivity based of a layered composition of titanium – nickel was tested, it was qualitatively shown that the use of platinum and aluminum leads to the formation of Schottky junction.
FET structure was designed based on the delta-doped diamond layer, including Schottky contacts. Transistor model with delta-layer was developed, taking into account the different law of mobility change and incomplete ionization in different regions of the transistor structure. The influence of the depth of the delta layer on the IV and CV characteristics of the transistor was considered. The critical impact on the main transistor characteristics of the source and drain ohmic contacts quality was determined.
It was shown that the transistor on hydrogenated diamond has low stability and low process reproducibility. Experimental samples of transistor structures based on the delta-doped diamond, that are most technologically stable and reproducible compared to transistors based on hydrogenated diamond were fabricated.
Transistor effect (control of channel conductivity) was demonstrated on sample with delta-layer 1.4 nm thick.

Publications on the project:

O.A.Ivanov, A.L.Vikharev and A.M.Gorbachev, Experimental study of plasma decay in pulsed microwave discharges of H2, CH4 and their mixtures. Plasma Sources Sci. Technol., 25 (2016) 035017,

A.B.Muchnikov, D.B.Radishev, A.L.Vikharev, A.M.Gorbachev, A.V.Mitenkin, M.lN.Drozdov, Y.N.Drozdov, P.A.Yunin, Characterization of interfaces in mosaic CVD diamond crystal, Journal of Crystal Growth, 442 (2016) 62–67,

V.A. Kukushkin, Simulation of a perfect CVD diamond Schottky diode steep forward current–voltage characteristic, Physica B 498 (2016) 1–6,

A.V.Golubkov, A.S.Ivanov, V.A.Ilyin, V.V.Luchinin, S.A.Bogdanov, V.V.Chernov  and A.L.Vikharev, Stabilizing effect of diamond thin film on nanostructured silicon carbide field emission array, Journal of Vacuum Science & Technology B 34, 062202 (2016),

V.V. Chernov, A.M. Gorbachev, A.L. Vikharev, and M.A. Lobaev, Criterion for comparison of MPACVD reactors working at different microwave frequencies and diamond growth conditions, Phys. Status Solidi A, vol. 213, Issue 10, 2016, pp. 2564–2569,

A. Tumarkin, S. Razumov, A. Gagarin, A. Altynnikov, A. Mikhailov, R. Platonov, I. Kotelnikov, A. Kozyrev,  J. E. Butler, Ferroelectric Varactor on Diamond for Elevated Power Microwave Applications, IEEE Electron Device Letters, V.37, N.6, p. 762-765, June 2016,

J.E. Butler, A. Vikharev, A. Gorbachev, M. Lobaev, A. Muchnikov, D. Radischev, V. Isaev, V. Chernov, S. Bogdanov, M.l Drozdov, E. Demidov, E. Surovegina, V. Shashkin, A. Davidov, H. Tan, L. Meshi, A. C. Pakpour-Tabrizi, M.-L. Hicks, R. B. Jackman, Nanometric diamond delta doping with boron, Phys. Status Solidi RRL, 1–6 (2016),

Е.А. Суровегина, Е.В. Демидов, М.Н. Дроздов, А.В. Мурель, О.И. Хрыкин, В.И. Шашкин, М.А. Лобаев, А.М. Горбачев, А.Л. Вихарев, С.А. Богданов, В.А. Исаев, А.Б. Мучников, В.В. Чернов, Д.Б. Радищев, Д.Е. Батлер, Атомный состав и электрофизические характеристики эпитаксиальных слоев CVD алмаза, легированных бором, Физика и техника полупроводников, 2016, том 50, вып. 12, стр. 1595-1598