Theoretical study of high-density phases of covalent semiconductors. I.<i>Ab initio</i>treatment

Crain, Jason; Clark, S. J.; Ackland, Graeme J.; Payne, Michael; Milman, Victor; Hatton, P. D.; Reid, Benoit

doi:10.1103/physrevb.49.5329

Cited by 76 publications

(38 citation statements)

References 33 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Here ∆ǫ = −87 meV/at and ∆γ = +59 meV/at are the volume and surface contributions to the energy difference ∆E(N ), respectively. The value of ∆ǫ is smaller than the calculated energy difference between solid DIA and ST12 (for the bulk energy difference we find 130 meV/atom, in good agreement with previous calculations [28,29]). As indicated by the value of ∆γ = +59 meV/at, surface energy is smaller for ST12 clusters and its sign is opposite to that of the volume contribution to ∆E(N ).…”

supporting

confidence: 91%

Structure and stability of germanium nanoparticles

et al. 2001

View full text Add to dashboard Cite

In order to control and tailor the properties of nanodots, it is essential to separate the effects of quantum confinement from those due to the surface, and to gain insight into the influence of preparation conditions on the dot physical properties. We address these issues for the case of small Ge clusters (1-3 nm), using a combination of empirical and first-principles molecular dynamics techniques. Our results show that over a wide temperature range the diamond structure is more stable than tetragonal, ST12-like structures for clusters containing more than 50 atoms; however, the magnitude of the energy difference between the two geometries is strongly dependent on the surface properties. Based on our structural data, we propose a mechanism which may be responsible for the formation of metastable ST12 clusters in vapor deposition experiments, by cold quenching of amorphous nanoparticles with unsaturated, reconstructed surfaces.In semiconductor nanoparticles quantum confinement leads to an increase of the optical gap compared to the bulk value and thus opens new possibilities for controlling photoluminescence effects, with narrow emission spectra tunable over a wide range of wavelengths [1,2]. These properties make semiconductor dots attractive for many applications including photovoltaics, lasers and infrared dyes. Furthermore, their brightness, low toxicity and the ability to use a single excitation wavelength make them good alternatives to organic dyes for biological labelling, but their low water solubility has limited biological applications. However, recent experiments have shown that using specific coatings, the surface of selected semiconductor nanodots can be tailored to enhance the chemical interaction with a biological sample and the water solubility [3,4].Understanding the influence of surface reconstruction and passivation on the ground state properties of semiconductor nanodots is a key prerequisite not only in designing biological applications, but also for controlling deposition of nanoparticles on surfaces and aggregation of multiple dots into new structures. In order to tailor the properties of nanodots, it is important to separate the effects of quantum confinement from those due to the surface, and to gain insight into the mechanism by which preparation conditions can influence the dot atomic structure and thus its optical properties.Here we address these issues for the case of small Ge dots (1-3 nm), whose atomic structure is the most controversial amongst those of group IV and II-VI semiconductors. While some preparation techniques, including chemical methods [5][6][7][8][9], yield diamond-like Ge dots irrespective of size, several experiments [10-12] suggest a structural transition, as the dot diameter becomes smaller than 4-5 nm. In particular, some experiments [13,14] using vapor deposition techniques indicate a change from a cubic diamond (DIA) to a tetragonal structure, possibly ST12, in contrast to the behavior found for Si [15][16][17] and other II-VI dots [18,19]. In the bulk, the ST...

show abstract

supporting

confidence: 91%

Structure and stability of germanium nanoparticles

et al. 2001

View full text Add to dashboard Cite

show abstract

“…The stability of BC8 relative to diamond is apparently enhanced at high temperature, possibly as a result of additional degrees of freedom in bonding angle configurations (as geometrically described in ref. 38).…”

Section: Discussionmentioning

confidence: 99%

Carbon under extreme conditions: Phase boundaries and electronic properties from first-principles theory

Correa

Bonev

Galli

2006

Proc. Natl. Acad. Sci. U.S.A.

215

122

View full text Add to dashboard Cite

At high pressure and temperature, the phase diagram of elemental carbon is poorly known. We present predictions of diamond and BC8 melting lines and their phase boundary in the solid phase, as obtained from first-principles calculations. Maxima are found in both melting lines, with a triple point located at Ϸ850 GPa and Ϸ7,400 K. Our results show that hot, compressed diamond is a semiconductor that undergoes metalization upon melting. In contrast, in the stability range of BC8, an insulator to metal transition is likely to occur in the solid phase. Close to the diamond͞liquid and BC8͞liquid boundaries, molten carbon is a low-coordinated metal retaining some covalent character in its bonding up to extreme pressures. Our results provide constraints on the carbon equation of state, which is of critical importance for devising models of Neptune, Uranus, and white dwarf stars, as well as of extrasolar carbon-rich planets.phase transitions ͉ melting ͉ high pressure ͉ molecular dynamics ͉ metalization E lemental carbon has been known since prehistory, and diamond is thought to have been first mined in India Ͼ2,000 years ago, although recent archaeological discoveries point at the possible existence of utensils made of diamond in China as early as 4,000 before Christ (1). Therefore, the properties of diamond and its practical and technological applications have been extensively investigated for many centuries. In the last few decades, after the seminal work of Bundy and coworkers (2) in the 1950s and '60s, widespread attention has been devoted to studying diamond under pressure (3). For example, the properties of diamond and, in general, of carbon under extreme pressure and temperature conditions are needed to devise models of outer planet interiors (e.g., Neptune and Uranus) (4-6), white dwarfs (7, 8) and extrasolar carbon planets (9).Nevertheless, under extreme conditions the phase boundaries and melting properties of elemental carbon are poorly known, and its electronic properties are not well understood. Experimental data are scarce because of difficulties in reaching megabar (1 bar ϭ 100 kPa) pressures and thousands of Kelvin regimes in the laboratory. Theoretically, sophisticated and accurate models of chemical bonding transformations under pressure are needed to describe phase boundaries. In most cases, such models cannot be simply derived from fits to existing experimental data, and one needs to resort to first-principles calculations, which may be very demanding from a computational standpoint.It has long been known that diamond is the stable phase of carbon at pressures above several gigapascal (2). Total energy calculations (10, 11) based on Density Functional Theory (DFT) predict a transition to another fourfold coordinated phase with the BC8 symmetry ¶ at Ϸ1,100 GPa and 0 K, followed by a transition to a simple cubic phase at pressures Ͼ3,000 GPa. These transitions have not yet been investigated experimentally, because the maximum pressure reached so far in diamond anvil cell experiments on carbon is 140 GP...

show abstract

“…In particular, the ST12 structure is found as metastable phase [9] of Ge upon pressure release from the high pressure β-tin phase. It has not been found in Si, probably due to the large bond-angle deviations from the ideal tetrahedral angle in the diamond phase [10,11].…”

Section: Computational Detailsmentioning

confidence: 98%

Mn doping in model amorphous Si and Ge: A theoretical investigation

Continenza

Profeta

2010

J. Phys.: Conf. Ser.

View full text Add to dashboard Cite

The magnetic properties of (Cr, V)-doped ZnGeN 2 J Rufinus -An ab initio study of transition metals doped with WSe2 for long-range room temperature ferromagnetism in twodimensional transition metal dichalcogenide Carmen J Gil, Anh Pham, Aibing Yu et al. Abstract. We present a theoretical study on the structural, electronic and magnetic properties of Mn-doping in amorphous group IV-semiconductors. In order to understand the effect of local disorder on the properties of the system, we consider the ST12 structure, a 12-atom unit cell which is known to locally reproduce the coordination of amorphous semiconductors. Based on ab-initio calculations we predict enhanced magnetic properties and higher solubility of Mn ions in model amorphous systems suggesting that amorphous semiconductors can represent an alternative route for spintronic applications. IntroductionMn-doping in technologically relevant semiconductors is still catching the scientific community interest due to possible spintronic applications. The attention has so far been devoted mainly to III-V compounds achieving ferromagnetic temperatures up to 170K in GaAs [1]. Mn-doping in group IV semiconductors has also been experimentally achieved with more puzzling results. Low temperature MBE-growth of Mn-diluted Ge showed two different ferromagnetic transitions at 12K and 112K[2] compatible with an inhomogeneous distribution of dopants and the formation of bound magnetic polarons [3]. Solid solution methods [4] lead to Curie temperatures as high as 285K in partial agreement with co-deposition of Mn and Co in Ge which gave a transition temperature of 270K [5]. In all these reports the samples, doped with Mn-concentrations of the order of a few percent, are insulators with rather low carrier densities (mainly holes) while GaMnAs shows metallic behavior. Although most of the experiments are performed on crystalline samples, several experimental techniques used to achieve Mn-dilution within the semiconductor matrix cause a loss of short-range order making the structure locally more similar to an amorphous rather than to a perfect crystalline material. This is established by several structural studies performed, for example, on ion-implanted samples [6] showing their disordered short-range nature depending on the implantation temperature, the ion dose and subsequent annealing treatments. In addition, Mn-and Cr-cosputtering has been realized for both Ge [7] and Si[8] revealing interesting magnetic properties of samples at quite large impurity concentrations (up to 22 %) still preserving the dilution limit and avoiding precipitation of impurity-rich compounds. In fact, large impurity concentrations are expected to enhance the magnetic properties of such materials: however, rather poor ferromagnetism was revealed and indeed paramagnetic behavior has been reported for Mn-doped amorphous Si. This behavior was ascribed to a large number of dangling bonds that trap carriers locally generated by dopants.

show abstract

Theoretical study of high-density phases of covalent semiconductors. I.Ab initiotreatment

Cited by 76 publications

References 33 publications

Structure and stability of germanium nanoparticles

Structure and stability of germanium nanoparticles

Carbon under extreme conditions: Phase boundaries and electronic properties from first-principles theory

Mn doping in model amorphous Si and Ge: A theoretical investigation

Contact Info

Product

Resources

About