| 1. |
- 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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| 2. |
- 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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| 3. |
- Djurberg, Viktor, 1993-
(författare)
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Low Temperature Charge Transport in Diamond
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Diamond is a wide band semiconductor with fascinating electrical and physical properties. It has high thermal and electrical conductivity, high electrical breakdown field, high radiation hardness and is chemically inert. These properties make diamond an excellent material for high power electronics, high frequency electronics, particle detectors and for electronics in hazardous environments. Moreover, diamond has been suggested for applications in valleytronics.Valleytronics is a term for semiconductor technology that exploits minima in an energy band, so called valleys. In diamond there are six of these valleys in the conduction band and the conduction electrons resides in one of these six valleys at low temperatures. The valley an electron is in, its valley polarization, affects how it behaves in an electric field. The valley polarization along with an understanding of the electron-phonon scattering processes makes a good framework for understanding of electron transport in diamond. In this thesis, both of these topics have been explored, with the purpose of understanding low temperature electron transport in diamond. A detailed description of low temperature charge transport is relevant for several reasons. Firstly, it can help with understanding the charge transport in e.g. detectors. Secondly, it gives more degrees of freedom when designing new electronics. In this thesis, both experiments and simulations has been used investigate low temperature transport in diamond. The main experiment method used was time-of-flight were the drift current of valley polarized electrons measured between two contacts. These experiment could then be compared with Monte Carlo simulations. The simulations gave valuable insigne into the dynamics of the electrons. This self-written code for Monte Carlo simulations is described in greater detail in this thesis. Some highlighted results of this thesis are as follows: optical observations of valley polarized diffusion, electrical control of valley polarized currents and the estimations of the acoustic deformation potentials to Du = 18.5 eV and Dd = -5.7 eV. This thesis also includes a more general part about charge transport.
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| 4. |
- 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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| 5. |
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| 6. |
- Hinnemo, Malkolm, 1986-, et al.
(författare)
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On Monolayer Formation of Pyrenebutyric Acid on Graphene
- 2017
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 33:15, s. 3588-3593
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Tidskriftsartikel (refereegranskat)abstract
- As a two-dimensional material with high charge carrier mobility, graphene may offer ultrahigh sensitivity in biosensing. To realize this, the first step is to functionalize the graphene. This is commonly done by using 1-pyrenebutyric acid (PBA) as a linker for biornolecules. However, the adsorption of PBA on graphene remains poorly understood despite reports of successful biosensors functionalized via this route. Here, the PBA adsorption on graphene is characterized through a combination of Raman spectroscopy, ab initio calculations, and spectroscopic ellipsometry. The PBA molecules are found to form a self-assembled monolayer on graphene, the formation of which is self-limiting and Langmuirian. Intriguingly, in concentrated solutions, the PBA molecules are found to stand up and stack horizontally with their edges contacting the graphene surface. This morphology could facilitate a surface densely populated with carboxylic functional groups. Spectroscopic analyses show that the monolayer saturates at 5.3 PBA molecules per nm(2) and measures similar to 0.7 nm in thickness. The morphology study of this PBA monolayer sheds light on the pi-pi stacking of small-molecule systems on graphene and provides an excellent base for optimizing functionalization procedures.
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| 7. |
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| 8. |
- Konishi, Kazuki, et al.
(författare)
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Low-temperature mobility-lifetime product in synthetic diamond
- 2020
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 117:21
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Tidskriftsartikel (refereegranskat)abstract
- The mobility-lifetime (μτ) product is an important parameter that determines the performance of electronic and photonic devices. To overcome the previously reported difficulties in measuring the μτ product at cryogenic temperatures, we implement a time-resolved cyclotron resonance method to determine the carrier lifetime τ. After clarifying the difference between the AC and DC mobilities measured by cyclotron resonance and time-of-flight methods, respectively, we demonstrate an inverse temperature dependence of the μτ product. The highest recorded μτ product of 0.2 cm2/V, which is approximately 100 times the room-temperature value, was obtained at 2 K for chemical-vapor-deposition diamond of the highest currently available purity.
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| 9. |
- Majdi, Saman, 1977-, et al.
(författare)
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Carrier Scattering Mechanisms : Identification via the Scaling Properties of the Boltzmann Transport Equation
- 2021
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Ingår i: Advanced Theory and Simulations. - : John Wiley & Sons. - 2513-0390. ; 4:1
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Tidskriftsartikel (refereegranskat)abstract
- A method based on the scaling properties of the Boltzmann transport equation is proposed to identify the dominant scattering mechanisms that affect charge transport in a semiconductor. This method uses drift velocity data of mobile charges at different lattice temperatures and applied electric fields and takes into account the effect of carrier heating. By performing time‐of‐flight measurements on single‐crystalline diamond, hole and electron drift velocities are measured under low‐injection conditions within the temperature range 10–300 K. Evaluation of the data using the proposed method identifies acoustic phonon scattering as the dominant scattering mechanism across the measured temperature range. The exception is electrons at 100–200 K where conduction‐band valley repopulation has a prominent effect. At temperatures below ≈80 K, where valley polarization is observed for electrons, transport dominated by acoustic phonon scattering is observed in different valleys separately. The scaling model is additionally tested on data from highly resistive gallium arsenide samples to demonstrate the versatility of the method. In this case, impurity scattering can be ruled out as the dominant scattering mechanism in the samples for the temperature range 80–120 K.
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| 10. |
- Majdi, Saman, 1977-, et al.
(författare)
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Enhanced Hall mobility in graphene-on-electronic-grade diamond
- 2023
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 123:1
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Tidskriftsartikel (refereegranskat)abstract
- The outstanding electronic properties of graphene make this material a candidate for many applications, for instance, ultra-fast transistors. However, self-heating and especially the detrimental influence of available supporting substrates have impeded progress in this field. In this study, we fabricate graphene-diamond heterostructures by transferring graphene to an ultra-pure single-crystalline diamond substrate. Hall-effect measurements were conducted at 80 to 300 K on graphene Hall bars to investigate the charge transport properties in these devices. Enhanced hole mobility of 2750 cm(2) V-1 s(-1) could be observed at room-temperature when using diamond with reduced nitrogen (N-s(0)) impurity concentration. In addition, by electrostatically varying the carrier concentration, an upper limit for mobility is determined in the devices. The results are promising for enabling carbon-carbon (C-C) devices for room-temperature applications.
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