Some Papers by Jan Isberg
Transistors operating at high frequencies are the basic building blocks of millimeter-wave commun... more Transistors operating at high frequencies are the basic building blocks of millimeter-wave communication and sensor systems. The high charge-carrier mobility and saturation velocity in graphene can open way for ultrafast field-effect transistors with a performance even better than what can be achieved with III-V-based semiconductors. However, the progress of high-speed graphene transistors has been hampered by fabrication issues, influence of adjacent materials, and self-heating effects. Here, we report on the improved performance of graphene field-effect transistors (GFETs) obtained by using a diamond substrate. An extrinsic maximum frequency of oscillation f max of up to 54 GHz was obtained for a gate length of 500 nm. Furthermore, the high thermal conductivity of diamond provides an efficient heat-sink, and the relatively high optical phonon energy of diamond contributes to an increased charge-carrier saturation velocity in the graphene channel. Moreover, we show that GFETs on diamond exhibit excellent scaling behavior for different gate lengths. These results promise that the GFET-on-diamond technology has the potential of reaching sub-terahertz frequency performance.
Nature Materials, Jul 14, 2013
Standard electronic devices encode bits of information by controlling the amount of electric char... more Standard electronic devices encode bits of information by controlling the amount of electric charge in the circuits. Alternatively, it is possible to make devices that rely on other properties of electrons than their charge. For example, spintronic devices make use of the electron spin angular momentum as a carrier of information. A novel concept is valleytronics in which information is encoded by the valley quantum number of the electron. The analogy between the valley and spin degrees of freedom also implies the possibility of valley-based quantum computing. Utilizing the valley degree of freedom requires that the material has two or more conduction band valleys with the same energy minima but located at different positions in momentum space. In this article we demonstrate for the first time generation, transport (across macroscopic distances) and detection of valley polarized electrons in bulk diamond with a relaxation time of 300 ns at 77 K. We anticipate that these results will form the basis for the development of integrated valleytronic devices.
Science, 2002
most susceptible to the impact of pollution aerosols on their albedo (27). However, the findings ... more most susceptible to the impact of pollution aerosols on their albedo (27). However, the findings here suggest that this susceptibility does not translate into large sensitivity to anthropogenic land-based aerosols as currently believed, for two reasons: (i) Aerosols in a cloudy marine boundary layer are deposited quickly by cloud processes; and (ii) when pollution aerosols manage to interact with clouds over the sea, the sea salt reduces the supersaturation and hence the droplet concentrations and cloud albedo. These are likely causes for the larger cloud drop r eff for the same aerosol index over the ocean as compared to land (28), recently observed by satellite, which has been unexplained until now.
Applied Physics Letters, 2014
The stability of valley polarized electron states is crucial for the development of valleytronics... more 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.
Investigating the effects of local scattering mechanisms is of great importance to understand cha... more Investigating the effects of local scattering mechanisms is of great importance to understand charge transport in semiconductors. This article reports measurements of the hole transport properties of boron-doped (100) single-crystalline chemical vapor deposited diamond. A Timeof-Flight measurement using a 213 nm, pulsed UV laser for excitation, was performed on high-purity single-crystalline diamonds to measure the hole drift velocity in the low-injection regime. The measurements were carried out in the temperature range 10-80 K. The results obtained are directly applicable to low-temperature detector applications. By comparing our data to Monte-Carlo simulations, a detailed understanding of the dominating hole scattering mechanisms is obtained. V C 2013 AIP Publishing LLC [http://dx.
Journal of Applied Physics, 2011
The time-of-flight technique has been used to measure the drift velocities for electrons and hole... more The time-of-flight technique has been used to measure the drift velocities for electrons and holes in high-purity single-crystalline CVD diamond. Measurements were made in the temperature interval 83≤T≤460 K and for electric fields between 90 and 4×103 V/cm, applied in the ⟨100⟩ crystallographic direction. The study includes low-field drift mobilities and is performed in the low-injection regime to perturb the applied electric field only minimally.
Physica Status Solidi (a), 2008
Hall-effect measurements on single crystal boron-doped CVD diamond in the temperature interval 80... more Hall-effect measurements on single crystal boron-doped CVD diamond in the temperature interval 80–450 K are presented together with SIMS measurements of the dopant concentration. Capacitance–voltage measurements on rectifying Schottky junctions manufactured on the boron-doped structures are also presented in this context. Evaluation of the compensating donor (ND) and acceptor concentrations (NA) show that in certain samples very low compensation ratios (ND/NA below 10–4) have been achieved. The influence of compensating donors on majority carrier transport and the significance for diamond device performance are briefly discussed. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Advances in Science and Technology, 2006
Diamond exhibits the highest breakdown field and the highest carrier mobilities of any wide band ... more Diamond exhibits the highest breakdown field and the highest carrier mobilities of any wide band gap semiconductor. Because of these and other outstanding material properties, diamond potentially enables the development of high-voltage and high frequency electronic devices with superior performance. The high field electrical transport properties, in particular the breakdown field strength, ultimately determine the upper voltage limit for high voltage devices. Similarly, the high-field transport properties determine the upper cut-off frequency in high-frequency field effect transistors. In this paper we present preliminary measurements of the multiplication factor due to impact ionization in single crystal CVD diamond. The measurements were performed by alpha particle charge injection into Schottky diode structures biased at high voltage. The structures consist of a ~300 µm heavily boron doped layer together with a thinner low-doped layer in which the high field is concentrated.
International Journal of Engineering Science, 2005
In this article we present numerical studies of waves interacting with a cylindrical point absorb... more In this article we present numerical studies of waves interacting with a cylindrical point absorber that is directly driving a seabed based linear generator. For waves useful for power conversion, the wave/point absorber interaction can be modelled, using potential theory assuming an inviscid irrotational incompressible fluid. The generator is modelled as a viscous damper. This paper pays special attention to the case when the converter is in resonance with the wave. The power capture capability of the system has been studied both for a harmonic wave and for real ocean waves.
Diamond and Related Materials, 2003
There is significant academic and industrial interest in developing electronic devices for high-f... more There is significant academic and industrial interest in developing electronic devices for high-frequency, high-power and hightemperature applications. This interest has generated considerable research efforts in wide-bandgap semiconductors. Of these materials diamond has by far the most interesting and extreme properties, i.e. mechanical, optical, thermal as well as electronic. Diamond exhibits the highest breakdown field and thermal conductivity of any material and has the highest carrier mobilities of any wide-bandgap semiconductor, thereby enabling the development of electronic devices with superior performance with regards to power efficiency, power density, high-frequency properties, power loss and cooling. Nevertheless, the breakthrough of diamondbased electronics has not yet happened, largely due to the difficulty of synthesising high-quality single crystal diamond. Recent advances in growing intrinsic and boron-doped single crystal diamond intended for electronic applications have resulted in films with exceptionally low defect densities. In the intrinsic material we have reported measured room temperature drift mobilities of 4500 cm yV s for electrons and 3800 cm yV s for holes (Science 297 (2002) 1670). These mobility values were determined by 2 2
Proceedings of the 17 International Symposium on Power Semiconductor Devices & IC's May 23-26, 2005 Santa Barbara, CA, May 23, 2005
We present our findings on the numerical and
experimental analysis of diamond Schottky Barrier
... more We present our findings on the numerical and
experimental analysis of diamond Schottky Barrier
diodes (SBDs) comprising of intrinsic single crystal (SC)
chemical vapour deposited (CVD) diamond layers
grown on highly boron doped substrates also grown by
CVD. Good correlation with experimental results has
been achieved through numerical modelling that has
incorporated previously reported data on transport
physics and carrier activation. With our numerical model,
we are able to match to within 12 to 15% of the
measured forward characteristics of fabricated diamond
SBDs up to 2 V in excess of the turn on voltage, for two
different Schottky metals.
IEEE Transactions on Electron Devices, 2004
A high-voltage transmission line pulse transformer has been constructed based on modem cable tech... more A high-voltage transmission line pulse transformer has been constructed based on modem cable technology. The transformer has been successfully tested for secondary voltages up to 85 kV. The high-voltage cable is equipped with a resistive layer (semicon) on the inner conductor and on the inside of the outer conductor. Semicon cables are commonly used in high-voltage transmission of electrical power.
IEEE Transactions on Electron Devices, 2008
High-quality electronic-grade intrinsic chemicalvapor-deposited (CVD) single-crystal diamond laye... more High-quality electronic-grade intrinsic chemicalvapor-deposited (CVD) single-crystal diamond layers having exceptionally high carrier mobilities have been reported by Isberg et al. This makes the realization of novel electronic devices in diamond, particularly for high-voltage and high-temperature applications, a viable proposition. As such, material models which can capture the particular features of diamond as a semiconductor are required to analyze, optimize, and quantitatively design new devices. For example, the incomplete ionization of boron in diamond and the transition to metallic conduction in heavily boron-doped layers require accurate carrier freeze-out models to be included in the simulation of diamond devices. Models describing these phenomena are proposed in this paper and include numerical approximation of intrinsic diamond which is necessary to formulate doping-and temperature-dependent mobility models. They enable a concise numerical description of single-crystal diamond which agrees with data obtained from material characterization. The models are verified by application to new Schottky m-i-p + diode structures in diamond. Simulated forward characteristics show excellent correlation with experimental measurements. In spite of the lack of impact ionization data for single-crystal diamond, approximation of avalanche coefficient parameters from other wide-bandgap semiconductors has also enabled the reverse blocking characteristics of diamond diodes to be simulated. Acceptable agreement with breakdown voltage from experimental devices made with presently available single-crystal CVD diamond is obtained.
Diamond and Related Materials, 2006
The modelling of Schottky m-i-p + (SMIP) diodes fabricated on chemical vapour deposited (CVD) sin... more The modelling of Schottky m-i-p + (SMIP) diodes fabricated on chemical vapour deposited (CVD) single crystal (SC) diamond intrinsic layers grown on highly boron doped CVD diamond substrates is reported. Variations in intrinsic layer thickness, Schottky metal type and operating temperature have been included in the analysis. Numerical models that take into account the activation of dopants, concentration and temperature dependant mobility and avalanche coefficients have been derived to successfully simulate experimental diamond devices. D
Physica Status Solidi (a), 2005
Hole transport properties in high-purity single crystal CVD diamond samples were studied using th... more Hole transport properties in high-purity single crystal CVD diamond samples were studied using the time of flight technique with optical excitation of the carriers. The measurements were taken at different temperatures in the interval 80–470 K. By varying the intensity of the optical excitation over several orders of magnitude, measurements at different carrier concentrations have been performed. In this way, measurements have been made both in the space charge limited and non space charge limited regimes, with consistent results. The temperature dependence of the low-field hole drift mobility shows a Tα dependence with α ≈ –1.5, below 350 K. This indicates that acoustic phonon scattering is the dominant scattering mechanism and a very low concentration of ionized impurities in this material. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Diamond and Related Materials, 2001
In this paper we report an experimental study of photocurrent mobility = lifetime products and fr... more In this paper we report an experimental study of photocurrent mobility = lifetime products and free carrier lifetimes in CVD grown polycrystalline diamond of various qualities. The investigated samples are low impurity samples, nitrogen content ; 10 15 cm y3 , with an average grain size ranging from 25 m up to 110 m. This large difference in average grain size makes it possible to distinguish effects due to lifetime limiting trapping and recombination defect centers inside the grains from effects caused by defect centers at grain boundaries. At low carrier densities, -10 13 cm y3 , the effective free carrier lifetime is in the sub-nanosecond to nanosecond range in all samples due to intra-grain trapping and recombination centers. At high carrier densities, ) 10 13 cm y3 , the intra-grain centers becomes saturated and the effective lifetime becomes predominately given by carrier diffusion to and recombination at the defects related to the grain boundaries. Hence, the effective lifetime at high carrier densities is strongly related to the average grain size and increases up to several tens of nanoseconds, in samples with a large average grain size, whereas it remains in the nanosecond range for samples with small average grain size. In addition, we observe a lower mobility = lifetime product and decay constant with increasing nitrogen content, clearly showing the negative influence of nitrogen and nitrogen-related defects on these important material parameters. ᮊ
Carbon, 2005
Semiconducting boron doped single-crystal CVD diamond has been patterned using aluminum masks and... more Semiconducting boron doped single-crystal CVD diamond has been patterned using aluminum masks and an inductively coupled plasma (ICP) etch system. For comparison insulating HPHT diamond samples were also patterned using the same process. Diamond etch rates above 200 nm/min were obtained with an O 2 /Ar discharge for a gas pressure of 2.5 mTorr using 600 W RF power. We have accomplished the fabrication of structures with a minimum feature size of 1 lm with vertical sidewalls in both CVD and HPHT diamond. The ICP etching produced smooth surfaces with a typical root-mean-square surface roughness of 3 nm. The dependence of etch rate on bias voltage was somewhat different for the two types of diamond. However, for all samples both the etch rate and anisotropy were found to improve with increasing bias voltage.
Renewable Energy, 2006
Motions in nature, for example ocean waves, can play a significant role in tomorrow's electricity... more Motions in nature, for example ocean waves, can play a significant role in tomorrow's electricity production, but the constructions require adaptations to its media. Engineers planning hydropower plants have always taken natural conditions, such as fall height, speed of flow, and geometry, as basic design parameters and constraints in the design. The present paper describes a novel approach for electric power conversion of the vast ocean wave energy. The suggested linear electric energy converter is adapted to the natural wave motion using straightforward technology. Extensive simulations of the wave energy concept are presented, along with results from the experimental setup of a multisided permanent magnet linear generator. The prototype is designed through systematic electromagnetic field calculations. The experimental results are used for the verification of measurements in the design process of future full-scale direct wave energy converters. The present paper, describes the energy conversion concept from a system perspective, and also discusses the economical and some environmental considerations for the project. q
IEEE Transactions on Energy Conversion, 2005
The possibility to use three-phase permanent magnet linear generators to convert sea wave energy ... more The possibility to use three-phase permanent magnet linear generators to convert sea wave energy into electric energy is investigated by multiphysics simulations. The results show a possibility, which needs to be further verified by experimental tests, for a future step toward a sustainable electric power production from ocean waves by using direct conversion. The results suggest that wave energy can have an impact on tomorrow's new sustainable electricity production, not only for large units, but also for units ranging down to 10 kW. This gives wave power a larger economical potential than previously estimated. The study demonstrates the feasibility of computer simulations to give a broad, and in several aspects a detailed, understanding of the energy conversion. The simulation results also give a useful starting point for future experimental work.
IEEE Journal of Oceanic Engineering, 2006
In this paper, we compare simulated forces and accelerations for a moored floating buoy with full... more In this paper, we compare simulated forces and accelerations for a moored floating buoy with full-scale experimental results in real ocean waves. The buoy is moored with a wire connected by springs to a concrete foundation situated at the seafloor. This study aims to develop a computer model using potential theory with a linearized free-surface boundary condition to describe the motion of such a system. The intention is to use the model for future study of wave-energy absorption and design of converters. Another objective is to see how complex a model is required to get accurate results. The method used is computationally fast and makes it possible to couple linear buoy wave interaction with nonlinear generator models, so that different loads and latching can be studied. A computationally fast method is required to model farms of wave-energy converters.
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Some Papers by Jan Isberg
experimental analysis of diamond Schottky Barrier
diodes (SBDs) comprising of intrinsic single crystal (SC)
chemical vapour deposited (CVD) diamond layers
grown on highly boron doped substrates also grown by
CVD. Good correlation with experimental results has
been achieved through numerical modelling that has
incorporated previously reported data on transport
physics and carrier activation. With our numerical model,
we are able to match to within 12 to 15% of the
measured forward characteristics of fabricated diamond
SBDs up to 2 V in excess of the turn on voltage, for two
different Schottky metals.
experimental analysis of diamond Schottky Barrier
diodes (SBDs) comprising of intrinsic single crystal (SC)
chemical vapour deposited (CVD) diamond layers
grown on highly boron doped substrates also grown by
CVD. Good correlation with experimental results has
been achieved through numerical modelling that has
incorporated previously reported data on transport
physics and carrier activation. With our numerical model,
we are able to match to within 12 to 15% of the
measured forward characteristics of fabricated diamond
SBDs up to 2 V in excess of the turn on voltage, for two
different Schottky metals.
the lateral ToF geometry, carriers travel close to the sample surface and the system is therefore particularly
suited for studies of thin layers as well as the influence of different surface conditions on transport dynamics.
A 213 nm pulsed UV laser is used to create electron–hole pairs along a line focus between two parallel metal
electrodes on one surface. The use of reflective UV-optics with short focal length allows for a narrow focal
line and also for imaging the sample in UV or visible light without any dispersion. A clear hole transit was
observed in one homoepitaxial single crystalline diamond film for which the substrate was treated by a Ar/Cl
plasma etch prior to deposition. The hole transit signal was sufficiently clear to measure the near-surface hole
drift mobility of about 860 cm2/Vs across a contact spacing of 0.3 mm.
and synthetic diamond has been studied by secondary ion mass spectrometry. Ion implantation of
300 keV, 11B-ions to a dose of 2×10^14 cm-2 has been performed. The samples are subsequently
annealed at temperatures ranging from 800 to 1650 °C for 5 minutes up to 8 hours. In silicon and
silicon carbide, the boron diffusion is attributed to a transient process and the level of out-diffusion
is correlated to intrinsic carrier concentration. No transient, out-diffused, boron tail is revealed in
diamond at these temperatures.
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.