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Low Temperature Hole Transport in Single Crystal Synthetic Diamond
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
2012 (English)In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795Article in journal (Refereed) Published
Abstract [en]

Hole transport properties of boron-doped single-crystalline (SC) CVD diamond, growth in the<100> crystallographic direction, has been investigated. The measurement was carried out in thetemperature range 10  T  80 K. A Time-of-Flight (ToF) measurement, using a 213 nm, pulsedultraviolet laser for excitation was performed on high-purity SC diamonds to study hole driftmobility in the low-injection regime and the scattering mechanisms involved in the process. Asaturation of the hole mobility was observed. This indicates that impurity scattering is thedominating scattering process at these low temperatures.

Place, publisher, year, edition, pages
2012.
Keyword [en]
ToF, time-of-flight, scattering, drift velocity, CVD diamond, single crystal diamond
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-173598OAI: oai:DiVA.org:uu-173598DiVA: diva2:524558
Available from: 2012-05-02 Created: 2012-05-01 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Experimental Studies of Charge Transport in Single Crystal Diamond Devices
Open this publication in new window or tab >>Experimental Studies of Charge Transport in Single Crystal Diamond Devices
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Diamond is a promising material for high-power, high-frequency and high- temperature electronics applications, where its outstanding physical properties can be fully exploited. It exhibits an extremely high bandgap, very high carrier mobilities, high breakdown field strength, and the highest thermal conductivity of any wide bandgap material. It is therefore an outstanding candidate for the fastest switching, the highest power density, and the most efficient electronic devices obtainable, with applications in the RF power, automotive and aerospace industries. Lightweight diamond devices, capable of high temperature operation in harsh environments, could also be used in radiation detectors and particle physics applications where no other semiconductor devices would survive.

The high defect and impurity concentration in natural diamond or high-pressure-high-temperature (HPHT) diamond substrates has made it difficult to obtain reliable results when studying the electronic properties of diamond. However, progress in the growth of high purity Single Crystal Chemical Vapor Deposited (SC-CVD) diamond has opened the perspective of applications under such extreme conditions based on this type of synthetic diamond.

Despite the improvements, there are still many open questions. This work will focus on the electrical characterization of SC-CVD diamond by different measurement techniques such as internal photo-emission, I-V, C-V, Hall measurements and in particular, Time-of-Flight (ToF) carrier drift velocity measurements. With these mentioned techniques, some important properties of diamond such as drift mobilities, lateral carrier transit velocities, compensation ratio and Schottky barrier heights have been investigated. Low compensation ratios (ND/NA) < 10-4 have been achieved in boron-doped diamond and a drift mobility of about 860 cm2/Vs for the hole transit near the surface in a lateral ToF configuration could be measured. The carrier drift velocity was studied for electrons and holes at the temperature interval of 80-460 K. The study is performed in the low-injection regime and includes low-field drift mobilities. The hole mobility was further investigated at low temperatures (10-80 K) and as expected a very high mobility was observed.

In the case of electrons, a negative differential mobility was seen in the temperature interval of 100-150K. An explanation for this phenomenon is given by the intervally scattering and the relation between hot and cold conduction band valleys. This was observed in direct bandgap semiconductors with non-equivalent valleys such as GaAs but has not been seen in diamond before.

Furthermore, first steps have been taken to utilize diamond for infrared (IR) radiation detection. To understand the fundamentals of the thermal response of diamond, Temperature Coefficient of Resistance (TCR) measurements were performed on diamond Schottky diodes which are a candidate for high temperature sensors. As a result, very high TCR values in combination with a low noise constant (K1/f) was observed.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. 67 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 944
Keyword
Single crystal diamond, carrier transport, CVD diamond, time-of-flight, mobility, IR detector, compensation, diamond diode, drift velocity, thermal detector
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-173599 (URN)978-91-554-8391-3 (ISBN)
Public defence
2012-06-05, Häggsalen, Lägerhyddsvägen 1, Ångströmlaboratoriet, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2012-05-15 Created: 2012-05-01 Last updated: 2013-01-07Bibliographically approved
2. Diamond Based Electronics and Valleytronics: An experimental study
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. 61 p.
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

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