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| 2. |
- Asad, M., et al.
(författare)
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Graphene FET on Diamond for High-Frequency Electronics
- 2022
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Ingår i: IEEE Electron Device Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 0741-3106 .- 1558-0563. ; 43:2, s. 300-303
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Tidskriftsartikel (refereegranskat)abstract
- 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 ultra-fast 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 fmax 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.
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| 3. |
- Balmer, Richard S., et al.
(författare)
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Transport behavior of holes in boron delta-doped diamond structures
- 2013
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 113:3, s. 033702-
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Tidskriftsartikel (refereegranskat)abstract
- Boron delta-doped diamond structures have been synthesized using microwave plasma chemical vapor deposition and fabricated into FET and gated Hall bar devices for assessment of the electrical characteristics. A detailed study of variable temperature Hall, conductivity, and field-effect mobility measurements was completed. This was supported by Schrodinger-Poisson and relaxation time calculations based upon application of Fermi's golden rule. A two carrier-type model was developed with an activation energy of similar to 0.2 eV between the delta layer lowest subband with mobility similar to 1 cm(2)/Vs and the bulk valence band with high mobility. This new understanding of the transport of holes in such boron delta-doped structures has shown that although Hall mobility as high as 900 cm(2)/Vs was measured at room temperature, this dramatically overstates the actual useful performance of the device.
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| 4. |
- Djurberg, Viktor, et al.
(författare)
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Determination of the acoustic phonon deformation potentials in diamond
- 2022
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 106:4
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Tidskriftsartikel (refereegranskat)abstract
- The interaction between acoustic phonons and electrons in diamond has been investigated by comparing state-of-the-art time-of-flight drift velocity measurements with Monte Carlo simulations. We use a multivariable anisotropic description of acoustic deformation potential scattering. The phonon-electron interaction is the limiting factor for the carrier mobility in ultrapure single crystal diamond. Hence, having a correct description is necessary for both device simulations and for predicting the maximum device performance. The experiments were performed at low temperature and using ultrapure diamond to minimize the influence of other scattering sources. The electronic valley polarization in diamond at low temperatures enables determination of both uniaxial and dilatation deformation potentials in the same experiment. The uniaxial and dilatation deformation potentials are found to be 18.5±0.2 and −5.7±0.3 eV, respectively.
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| 5. |
- Djurberg, Viktor, et al.
(författare)
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Investigation of Photoexcitation Energy Impact on Electron Mobility in Single Crystalline CdTe
- 2021
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Ingår i: Materials. - : MDPI. - 1996-1944. ; 14:15
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Tidskriftsartikel (refereegranskat)abstract
- The exceptional electronic properties of cadmium telluride (CdTe) allow the material to be used in a wide range of high energy radiation detection applications. Understanding the mechanisms of local carrier scattering is of fundamental importance to understand the charge transport in the material. Here, we investigate the effect of photoexcitation on electron transport properties in chlorine doped single crystalline cadmium telluride (SC-CdTe:Cl). For this purpose time of flight measurements were performed on SC-CdTe:Cl in order to study the electron drift mobility in the low injection regime. Measurements were made at the temperature intervals of 80 to 300 K, for an applied electric field between 270 and 1600 V/cm and for wavelengths of 532, 355 and 213 nm. We have found that the electron drift mobility was affected by the excitation energy for temperatures below 200 K. In addition, the measurements revealed that it is possible to determine impurity and shallow trap concentration by this method. The method proves to be extremely sensitive in measuring very low impurity levels and in identifying dominant scattering mechanisms.
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| 6. |
- Djurberg, Viktor, et al.
(författare)
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Optical detection of valley-polarized electron diffusion in diamond
- 2023
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Ingår i: Materials for Quantum Technology. - : Institute of Physics Publishing (IOPP). - 2633-4356. ; 3:2
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Tidskriftsartikel (refereegranskat)abstract
- Using the state of valley-polarization of electrons in solids is a promising new paradigm for information storage and processing. The central challenge in utilizing valley-polarization for this purpose is to develop methods for manipulating and reading out the final valley state. Here, we demonstrate optical detection of valley-polarized electrons in diamond. It is achieved by capturing images of electroluminescence from nitrogen-vacancy centers at the surface of a diamond sample that are excited by electrons drifting and diffusing through the sample. Monte Carlo simulations are performed to interpret the resulting experimental diffusion patterns. Our results give insight into the drift-diffusion of valley-polarized electrons in diamond and yield a way of analyzing the valley-polarization of ensembles of electrons.
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| 7. |
- Gabrysch, Markus, et al.
(författare)
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Compensation in boron-doped CVD diamond
- 2008
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Ingår i: Physica status solidi. A, Applications and Materials Science. - : Wiley. - 1862-6300. ; 205:9, s. 2190-2194
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Tidskriftsartikel (refereegranskat)abstract
- 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 (N-D) and acceptor concentrations (N-A) show that in certain samples very low compensation ratios (N-D/N-A 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.
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| 8. |
- Gabrysch, Markus, 1978-, et al.
(författare)
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Electron and hole drift velocity in chemical vapor deposition diamond
- 2011
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 109:6, s. 063719-
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 9. |
- Hammersberg, Johan, et al.
(författare)
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Stability of polarized states for diamond valleytronics
- 2014
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 104:23, s. 232105-
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 10. |
- Isberg, Jan, et al.
(författare)
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A lateral time-of-flight system for charge transport studies
- 2009
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Ingår i: Diamond and related materials. - Langford Lane, Kidlington, Oxford, OX5 1GB, United Kingdom : Elsevier Ltd. - 0925-9635 .- 1879-0062. ; 18:9, s. 1163-1166
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Tidskriftsartikel (refereegranskat)abstract
- A measurement system for lateral ToF charge carrier transport studies in intrinsic diamond is described. In 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 213nm 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 860cm2/Vs across a contact spacing of 0.3mm.
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