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Kumar Kovi, Kiran
Alternative names
Publications (10 of 17) Show all publications
Majdi, S., Gabrysch, M., Kumar Kovi, K., Suntornwipat, N., Friel, I. & Isberg, J. (2016). Low temperature conduction-band transport in diamond. Applied Physics Letters, 109(16), Article ID 162106.
Open this publication in new window or tab >>Low temperature conduction-band transport in diamond
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2016 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 109, no 16, article id 162106Article in journal (Refereed) Published
Abstract [en]

By performing Time-of-Flight measurements on high-purity single-crystalline chemical vapor deposited diamond, we are able to extract the electron drift velocity of valley-polarized electrons in the low-injection regime. The aim of this study is to improve the understanding of the mechanisms involved in the conduction-band transport of valley-polarized electrons. The measurements were carried out within the temperature range of 10-80 K, and the experimental results are systematically compared with Monte Carlo charge transport simulations. We observe a rapid enhancement of the electron mobility with decreasing temperature, which reveals that inelastic effects in electron-phonon scattering become important below similar to 40 K. In addition, we obtain the momentum relaxation rate for electrons with different valley polarizations.

National Category
Condensed Matter Physics Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-310010 (URN)10.1063/1.4964720 (DOI)000386933200020 ()
Funder
Swedish Research Council, 621-2014-6026ÅForsk (Ångpanneföreningen's Foundation for Research and Development), 15-288Carl Tryggers foundation , 14:151 15:225Swedish National Infrastructure for Computing (SNIC), SNIC2014-3-65
Available from: 2016-12-12 Created: 2016-12-09 Last updated: 2018-04-15Bibliographically approved
Kovi, K. K., Vallin, Ö., Majdi, S. & Isberg, J. (2015). Inversion in Metal–Oxide–Semiconductor Capacitors on Boron-Doped Diamond. IEEE Electron Device Letters, 36(6), 603-605
Open this publication in new window or tab >>Inversion in Metal–Oxide–Semiconductor Capacitors on Boron-Doped Diamond
2015 (English)In: IEEE Electron Device Letters, ISSN 0741-3106, E-ISSN 1558-0563, Vol. 36, no 6, p. 603-605Article in journal (Refereed) Published
Abstract [en]

For the advancement of diamond-based electronic devices, the fabrication of metal-oxide-semiconductor field-effect transistors (MOSFETs) is crucial, as this device finds applications in numerous fields of power electronics and high-frequency systems. The MOS capacitor forms the basic building block of the MOSFET. In this letter, we describe planar MOS capacitor structures fabricated with atomic layer deposited aluminum oxide as the dielectric on oxygen-terminated boron-doped diamond substrates with different doping levels. Using capacitance-voltage measurements, we have, for the first time, observed inversion behavior in MOS structures on boron-doped diamond, with a doping concentration of 4.1 × 1019/cm3.

National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Electronics; Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-253954 (URN)10.1109/LED.2015.2423971 (DOI)000355252300025 ()
Available from: 2015-06-04 Created: 2015-06-04 Last updated: 2017-12-04Bibliographically approved
Kovi, K. K., Majdi, S., Gabrysch, M., Suntornwipat, N. & Isberg, J. (2015). (Invited) Surface Passivation of High-k Dielectric Materials on Diamond Thin Films. Paper presented at 228th ECS Meeting, Phoenix, October 11-15, 2015. ECS Transactions, 69, 61-65
Open this publication in new window or tab >>(Invited) Surface Passivation of High-k Dielectric Materials on Diamond Thin Films
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2015 (English)In: ECS Transactions, ISSN 1938-5862, E-ISSN 1938-6737, Vol. 69, p. 61-65Article in journal (Refereed) Published
Abstract [en]

Single-crystalline CVD diamond films have excellent electrical and material properties with potential in high power, high voltage and high frequency applications that are out of reach for conventional semiconductor materials. For realization of efficient devices (e.g. MOSFET), finding a suitable dielectric is essential to improve the reliability and electrical performance of devices. In the current study, we present results from surface passivation studies by high-k dielectric materials such as aluminum oxide and hafnium oxide deposited by ALD on intrinsic and boron doped diamond substrates. The hole transport properties in the intrinsic diamond films were evaluated and compared to unpassivated films using the lateral time-of-flight technique. The MOS capacitor structure, which forms the basic building block of the MOSFET, is discussed.

Keywords
Diamond, High Mobility Channel
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-268460 (URN)10.1149/06905.0061ecst (DOI)
Conference
228th ECS Meeting, Phoenix, October 11-15, 2015
Funder
Swedish Research Council
Available from: 2015-12-04 Created: 2015-12-04 Last updated: 2017-12-01
Kovi, K. K., Balmer, R. S. & Isberg, J. (2015). Semi-isotropic surface etching of diamond using a Faraday cage. Diamond and related materials, 58, 185-189
Open this publication in new window or tab >>Semi-isotropic surface etching of diamond using a Faraday cage
2015 (English)In: Diamond and related materials, ISSN 0925-9635, E-ISSN 1879-0062, Vol. 58, p. 185-189Article in journal (Refereed) Published
Abstract [en]

Etching of diamond is one of the most important process steps to realize diamond based devices. Isotropic etching in diamond yielding a high etch rate is challenging owing to its material properties. In the current study, single-crystalline diamond is etched using a Faraday cage that acts as the mask to attain semi-isotropic etching. An oxygen/chlorine plasma discharge with a pressure of 10 mTorr is used. The etching process is optimized by varying the applied plasma power, and the substrate bias together with varying parameters such as the thickness of the mask, the mask-to-diamond surface distance and the diameter of the holes in the mask. After optimization, semi-isotropic etched surface profiles up to a depth of 5 μm with an etch rate of 80 nm/min and surface roughness close to that of the unetched surface are achieved.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-259787 (URN)10.1016/j.diamond.2015.07.011. (DOI)000362137100027 ()
Available from: 2015-08-11 Created: 2015-08-11 Last updated: 2017-12-04Bibliographically approved
Kovi, K. K., Majdi, S., Gabrysch, M. & Isberg, J. (2014). A charge transport study in diamond, surface passivated by high-k dielectric oxides. Applied Physics Letters, 105(20), 202102
Open this publication in new window or tab >>A charge transport study in diamond, surface passivated by high-k dielectric oxides
2014 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 105, no 20, p. 202102-Article in journal (Refereed) Published
Abstract [en]

The recent progress in the growth of high-quality single-crystalline diamond films has sparked interest in the realization of efficient diamond power electronic devices. However, finding a suitable passivation is essential to improve the reliability and electrical performance of devices. In the current work, high-k dielectric materials such as aluminum oxide and hafnium oxide were deposited by atomic layer deposition on intrinsic diamond as a surface passivation layer. The hole transport properties in the diamond films were evaluated and compared to unpassivated films using the lateral time-of-flight technique. An enhancement of the near surface hole mobility in diamond films of up to 27% is observed when using aluminum oxide passivation.

National Category
Physical Sciences Engineering and Technology
Research subject
Engineering Science with specialization in Electronics
Identifiers
urn:nbn:se:uu:diva-229768 (URN)10.1063/1.4901961 (DOI)000345513300030 ()
Available from: 2014-08-13 Created: 2014-08-13 Last updated: 2017-12-05Bibliographically approved
Kovi, K. K., Suntornwipat, N., Majdi, S., Gabrysch, M., Hammersberg, J. & Isberg, J. (2014). Charge Transport Phenomena Unique to Diamond. MRS Online Proceedings Library, 1591, null-null
Open this publication in new window or tab >>Charge Transport Phenomena Unique to Diamond
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2014 (English)In: MRS Online Proceedings Library, Vol. 1591, p. null-nullArticle in journal (Refereed) Published
Abstract [en]

ABSTRACT Diamond is a unique material in many respects. One of the most well-known extreme properties of diamond is its ultrahardness. This property of diamond actually turns out to have interesting consequences for charge transport, in particular at low temperatures. In fact, the strong covalent bonds that give rise to the ultrahardness results in a lack of short wavelength lattice vibrations which has a strong impact on both electron and hole scattering. In some sense diamond behaves more like a vacuum than other semiconductor materials. In this paper we describe some interesting charge transport properties of diamond and discuss possible novel electronic applications.

Place, publisher, year, edition, pages
Cambridge Journals Online, 2014
Keywords
diamond, electrical properties, electron-phonon interactions
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-237485 (URN)10.1557/opl.2014.295 (DOI)null (ISBN)
Available from: 2014-12-03 Created: 2014-12-03 Last updated: 2018-04-15
Kovi, K. K. (2014). Diamond Based Electronics and Valleytronics: An experimental study. (Doctoral dissertation). Uppsala: Acta Universitatis Upsaliensis
Open this publication in new window or tab >>Diamond Based Electronics and Valleytronics: An experimental study
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Diamond is a promising semiconductor material for high power, high voltage, high temperature and high frequency applications due to its remarkable material properties: it has the highest thermal conductivity, it is the hardest material, chemically inert, radiation hard and has the widest transparency in the electromagnetic spectrum. It also exhibits excellent electrical properties like high breakdown field, high mobilities and a wide bandgap.  Hence, it may find applications in extreme conditions out of reach for conventional semiconductor materials, e.g. in high power density systems, high temperature conditions, automotive and aerospace industries, and space applications. 

 

With the recent progress in the growth of high purity single-crystalline CVD diamond, the realization of electronic devices is now possible. Natural and HPHT diamonds inevitably have too high a concentration of impurities and defects for electrical applications. To develop efficient electronic devices based on diamond, it is crucial to understand charge transport properties. Time-of-flight is one of the most powerful methods used to study charge transport properties like mobility, drift velocity and charge collection efficiency in highly resistive semiconductors, such as diamond. For commercial diamond devices to become a reality, it is necessary to have an effective surface passivation since the passivation determines the ability of a device to withstand high surface electric fields. Surface passivation studies on intrinsic SC-CVD diamond using materials like silicon oxide, silicon nitride and high-k materials have been conducted and observations reveal an increase in measured hole mobilities. Planar MOS capacitor structures form the basic building block of MOSFETs. Consequently, the understanding of MOS structures is crucial to make MOSFETs based on diamond. Planar MOS structures with aluminum oxide as gate dielectric were fabricated on boron doped diamond. The phenomenon of inversion was observed for the first time in diamond. In addition, low temperature hole transport in the range of 10-80 K has been investigated and the results are used to identify the type of scattering mechanisms affecting hole transport at these temperatures.

To utilize the potential of diamonds properties and with diamond being the hardest and most chemically inert material, new processing technologies are needed to produce devices for electrical, optical or mechanical applications. Etching of diamond is one of the important processing steps required to make devices. Achieving an isotropic etch with a high etch rate is a challenge. Semi-isotropic etch profiles with smooth surfaces were obtained by using anisotropic etching technique by placing diamond samples in a Faraday cage and etch rates of approximately 80 nm/min were achieved.

Valleytronics, which is a novel concept to encode information based on the valley quantum number of electrons has been investigated for the first time in diamond. Valley-polarized electrons with the longest relaxation time ever recorded in any material (300 ns) were observed. This is a first step towards demonstrating valleytronic devices.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2014. p. 61
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1163
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-229948 (URN)978-91-554-8999-1 (ISBN)
Public defence
2014-09-29, Polhemsalen, Ångström laboratory, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2014-09-05 Created: 2014-08-18 Last updated: 2014-12-02
Kovi, K. K., Majdi, S., Gabrysch, M. & Isberg, J. (2014). Silicon Oxide Passivation of Single-Crystalline CVD Diamond Evaluated by the Time-of-Flight Technique. ECS SOLID STATE LETT, 3(5), P65-P68
Open this publication in new window or tab >>Silicon Oxide Passivation of Single-Crystalline CVD Diamond Evaluated by the Time-of-Flight Technique
2014 (English)In: ECS SOLID STATE LETT, ISSN 2162-8742, Vol. 3, no 5, p. P65-P68Article in journal (Refereed) Published
Abstract [en]

The excellent material properties of diamond make it highly desirable for many extreme electronic applications that are out of reach of conventional electronic materials. For commercial diamond devices to become a reality, it is necessary to have an effective surface passivation since the passivation determines the ability of the device to withstand high surface electric fields. In this paper we present data from lateral Time-of-Flight studies on SiO2-passivated intrinsic single-crystalline CVD diamond. The SiO2 films were deposited using three different techniques. The influence of the passivation on hole transport was studied, which resulted in the increase of hole mobilities. The results from the three different passivations are compared. (C) 2014 The Electrochemical Society. All rights reserved.

National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-224497 (URN)10.1149/2.004405ssl (DOI)000333803500006 ()
Available from: 2014-05-14 Created: 2014-05-13 Last updated: 2014-09-08Bibliographically approved
Majdi, S., Kolahdouz, M., Moeen, M., Kovi, K. K., Balmer, R. S., Radamson, H. H. & Isberg, J. (2014). Single crystal diamond for infrared sensing applications. Applied Physics Letters, 105(16), 163510
Open this publication in new window or tab >>Single crystal diamond for infrared sensing applications
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2014 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 105, no 16, p. 163510-Article in journal (Refereed) Published
Abstract [en]

The synthesis of new materials for thermal infrared (IR) detection has been an intensive research area in recent years. Among new semiconductor materials, synthetic diamond has the ability to function even under very high temperature and high radiation conditions. In the present work, diamond Schottky diodes with boron concentrations in the range of 1014 < B < 1017 cm−3 are presented as candidates for IR thermal sensors with an excellent temperature coefficient of resistance (−8.42%/K) and very low noise levels around 6.6 × 10−15 V2/Hz. This enables huge performance enhancements for a wide variety of systems, e.g., automotive and space applications.

Keywords
Schottky diodes, diamond, infrared detectors
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-237486 (URN)10.1063/1.4899278 (DOI)000344363000092 ()
Available from: 2014-12-03 Created: 2014-12-03 Last updated: 2017-12-05Bibliographically approved
Hammersberg, J., Majdi, S., Kovi, K. K., Suntornwipat, N., Gabrysch, M., Twitchen, D. J. & Isberg, J. (2014). Stability of polarized states for diamond valleytronics. Applied Physics Letters, 104(23), 232105
Open this publication in new window or tab >>Stability of polarized states for diamond valleytronics
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2014 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 104, no 23, p. 232105-Article in journal (Refereed) Published
Abstract [en]

The stability of valley polarized electron states is crucial for the development of valleytronics. A long relaxation time of the valley polarization is required to enable operations to be performed on the polarized states. Here, we investigate the stability of valley polarized states in diamond, expressed as relaxation time. We have found that the stability of the states can be extremely long when we consider the electron-phonon scattering processes allowed by symmetry considerations. We determine electron-phonon coupling constants by Time-of-Flight measurements and Monte Carlo simulations and use these data to map out the relaxation time temperature dependency. The relaxation time for diamond can be microseconds or longer below 100 K and 100 V/cm due to the strong covalent bond, which is highly encouraging for future use in valleytronic applications. (C) 2014 AIP Publishing LLC.

National Category
Engineering and Technology Physical Sciences
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-229299 (URN)10.1063/1.4882649 (DOI)000337891200043 ()
Available from: 2014-08-06 Created: 2014-08-05 Last updated: 2018-04-15Bibliographically approved
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