Specific Heat of Si and Ge

Kagaya, Hideaki; Soma, T.

doi:10.1002/pssb.2221270147

Cited by 12 publications

(2 citation statements)

References 11 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The limiting low temperature value of was obtained. For the bulk crystal, the calculated θ D ≈ 413 K. This is in reasonable agreement with, but somewhat higher (by ≈ 10%) compared to, the observed standard value of θ D for Ge, which is 374 K. − It was found that the θ D for the Ge NW is about a factor of 1.57 lower than that of the Ge bulk crystal. This is an important result showing significant softening of low-frequency long-wavelength acoustic phonons and the associated elastic constants.…”

Section: Discussionsupporting

confidence: 78%

Phonons and Thermal Properties of Ge Nanowires: A Raman Spectroscopy Investigation and Phonon Simulations

Aggarwal

Sett

et al. 2022

J. Phys. Chem. C

View full text Add to dashboard Cite

We have investigated phonon an harmonicity related thermal properties [e.g., coefficient of thermal expansion (α), Gruneisen parameter (γ), and phonon mean free path as limited by Umklapp scattering (Λ mfp )] for Ge nanowires (NWs) using temperature-dependent Raman spectroscopy as well as phonon dynamics simulations. The experiments were carried out in two types of NW ensembles. One type of NWs has only the native oxide layer on Ge, and the other type has relatively thicker GeO 2 on the surface forming a core−shell structure. The temperature-dependent shift of the LO/TO Raman line of Ge (300 cm −1 ) was used to determine the αγ product in the temperature range of 80−800 K. The αγ product is enhanced compared to that observed in the bulk crystalline Ge over the whole temperature range. The experimental work was complimented by phonon simulations with quasi-harmonic approximation using density functional perturbation theory. The simulation allowed us to determine the thermodynamic parameters like bulk modulus, specific heat capacity (C v ), α, and γ. We have determined the anharmonicity coefficients and phonon lifetimes in Ge NWs and also estimated the Λ mfp arising from phonon−phonon scattering (Umklapp process). Comparison of the computed thermal parameters with the experimental data allowed us to place a confidence limit on the calculated parameters, which was used to separate out the two parameters αandγ for the NWs from the observed αγ product. The enhancement of α, in particular, in the Ge NWs has been explained as arising from significant softening of θ D in the NWs as observed from the low temperature C v calculated from the phonon simulations. Comparison of the computed phonon density of states shows appearance of excess weights in the phonon spectrum, which contributes to enhancement of heat capacity in NWs compared to that in the bulk.

show abstract

Section: Discussionsupporting

confidence: 78%

Phonons and Thermal Properties of Ge Nanowires: A Raman Spectroscopy Investigation and Phonon Simulations

Aggarwal

Sett

et al. 2022

J. Phys. Chem. C

View full text Add to dashboard Cite

show abstract

“…The thermal coefficient α , is found to be ~7.2 × 10 −5 eV/K for the low energy transition peak and slightly increases to 8.9 × 10 −5 eV/K for the high energy transition peak. This value of α is larger by approximately one order of magnitude as compared to that of the bulk semiconductor 27 . It can be seen that the thermal coefficient of the fitted peaks are dependent on their respective emission energy.…”

Section: Resultsmentioning

confidence: 77%

Carrier trapping and confinement in Ge nanocrystals surrounded by Ge3N4

Park

Chan

Reid

et al. 2016

Sci Rep

View full text Add to dashboard Cite

We investigated the optical properties of Ge nanocrystals surrounded by Ge 3 N 4 . The broad emission ranging from infrared to blue is due to the dependence on the crystal size and preparation methods. Here, we report high resolution Photoluminescence (PL) attributed to emission from individual Ge nanocrystals (nc-Ge) spatially resolved using micro-photoluminescence and detailed using temperature and power-dependent photoluminescence studies. The measured peaks are shown to behave with excitonic characteristics and we argue that the spread of the nc-Ge peaks in the PL spectrum is due to different confinement energies arising from the variation in size of the nanocrystals.Semiconductor nanostructures are arguably the most promising technology for future optoelectronics and memory device applications due to the recent rapid advances in nanoscale science and technqiues [1][2][3] . Ge is an indirect gap semiconductor, with two main electronic transitions, the first at 0.67 eV (indirect) the second at 0.8 eV (direct) and Ge nanocrystals (nc-Ge) are one of the candidates for such applications due to their superior charge storage performance [1][2][3] . Several methods can be used to form nc-Ge such as Ge ion implantation 4 , N 2 + implantation 5 , SiGe oxidation 6 , thermal annealing of Ge thin films 7,8 , molecular beam epitaxy 9, and co-deposition of Ge with SiO 2 3,10,11 . Ge nanocrystals have been shown to emit photoluminescence (PL) covering a vast spectrum in both the visible, with wavelengths ranging from 460 nm to 515 nm and in the infrared at around 1600 nm 4,10-17 . PL previously reported for nc-Ge has been shown to give broad emission spectra in the visible range with a full width at half maximum (FWHM) of a few hundred meV. This broad spectrum indicates an ensemble effect of the nanocrystals 4,10-15 , individual nc-Ge emission has never been resolved. The origin of visible PL from nc-Ge has been discussed by Kanemitsu et al. who reported a change in the Ge crystalline structure at diameters below 4 nm, departing from the usual diamond structure. This new structure, beyond the 4 nm limit, is thought to allow for their observed visible luminescence with the character of a direct transition 11 . Contrary to Kanemitsu, Giri et al. reported observation of PL from Ge nanocrystals of a larger diameter, 4~13 nm embedded in SiO 2 4 . In addition, S. Takeoka et al. measured PL that was dependent on Ge nanocrystals with average diameters of 0.9~5.3 nm embedded in SiO 2 . The PL was found to range from the near infrared at a diameter of 5.3 nm to an energy slightly larger than the band gap of bulk Ge as the nanocrystal size decreased down to 0.9 nm 17 . The broadness of the emission can be atributed to the dependence of the PL energy on nanocrystal size, but the precise explanation of the origin of this emission remains unclear. Ensemble effects have obscured the finer details of the PL spectrum, contributing to the controversy as to the origin of the Ge nanocrystal luminescence.In this paper, Ge nanocrystals with a d...

show abstract

Temperature Dependence of the Linear Thermal Expansion Coefficient for Si and Ge

Kagaya

Soma

1985

Physica Status Solidi (b)

View full text Add to dashboard Cite

1985) lied Physics and Mathematics, Mining College, Akita University PP Recently, we /1/ reported the results for the specific heat of S i and G e calculated from first principles using our previous works /2, 3/ based on the pseudopotential formalism and the local Heine-Abarenkov model potential.We /3/ obtained good agreement of phonon dispersion curves and specific heat with experimental data. In the present note, we study the thermal expansion of S i and Ge using our previous treatment /1 to 3/.vibrational i-mode, the mode Griineisen parameter ri( $ ) is defined and given As a measure of the volume (V) dependence of the frequency vi(d) of theThe averaged Griineisen constant is temperature-dependent and given by Here C.( 4 ) is the contribution of the corresponding mode t o the heat capacity at constant volume Cv given by 1 Using the temperature-dependent Griineisen constant ;y , the linear expansion coefficient oc is theoretically obtained as 1 , 1 ) Akita 01 0, Japan.

show abstract

Specific Heat of Si and Ge

Abstract: The thermal properties such as specific heat, thermal expansion coefficient, etc. of tetrahedrally covalent crystals have been experimentally studied (for instance, see /1, 2/), and the negative thermal expansion at low temperature

Cited by 12 publications

References 11 publications

Phonons and Thermal Properties of Ge Nanowires: A Raman Spectroscopy Investigation and Phonon Simulations

Phonons and Thermal Properties of Ge Nanowires: A Raman Spectroscopy Investigation and Phonon Simulations

Carrier trapping and confinement in Ge nanocrystals surrounded by Ge3N4

Temperature Dependence of the Linear Thermal Expansion Coefficient for Si and Ge

Contact Info

Product

Resources

About