Temperature dependence of Raman scattering in single crystal GaN films

Liu, Ming S.; Bursill, L. A.; Prawer, Steven; Nugent, K. W.; Tong, Yuzhen; Zhang, G. Y.

doi:10.1063/1.124083

Cited by 155 publications

(110 citation statements)

References 16 publications

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“…The temperature dependent Raman linewidths and shifts can be interpreted in the terms of anharmonic processes which results in a better understanding of electronic properties of (AlGa) 2 O 3 at different temperature. 16 Moreover, it has been demonstrated that the anharmonic constant which was extracted by analyzing anharmonic processes is very important for the MgZnO-based light emission device applications. 15 In this work, we reported on the temperature-dependence Raman scattering of β-(AlGa) 2 O 3 thin films with different Al content (0-0.72) in the temperature range from 77 to 300 K. In combination with detailed theoretical modellings for the frequency downshift and linewidths broadening, we can clearly illustrate the temperature effect on the Raman shift and linewidths in the β-(AlGa) 2 O 3 thin films, which provides an experimental basis for realization of (AlGa) 2 O 3 -based optoelectronic device applications.…”

Section: Introductionmentioning

confidence: 99%

Temperature dependence of Raman scattering in β-(AlGa)2O3 thin films

et al. 2016

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We report a detailed investigation on temperature-dependent Raman scattering of β-(AlGa)2O3 thin films with different Al content (0-0.72) under the temperature range of 77-300 K. The temperature-dependent Raman shifts and linewidths of the phonon modes were obtained by employing Lorentz fitting. The linewidths broadening of phonon modes with the temperature can be well explained by a model involving the effects of thermal expansion, lattice-mismatch-induced strain, and decay of optical phonon into two and three phonons. It is clearly demonstrated dependence of the linewidths and decay process on the Al content in β-(AlGa)2O3 thin films, which can provide an experimental basis for realization of (AlGa)2O3-based optoelectronic device applications.

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Section: Introductionmentioning

confidence: 99%

Temperature dependence of Raman scattering in β-(AlGa)2O3 thin films

et al. 2016

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“…In the Miller-Bravais index system (ℎ ℓ) [25], the -axis of the hexagonal crystal structure is chosen to be the [11][12][13][14][15][16][17][18][19][20] direction, and the -axis set equal to the -axis or [0001] direction [26]- [27]. In order to form a mutually orthogonal, right-handed coordinate system, the -axis is then chosen to be the [-1100] direction.…”

Section: Fig 1 (A)mentioning

confidence: 99%

“…where ( ) is the Stokes line position, is the absolute temperature, 0 is the Stokes line position at absolute zero temperature, and and are fitting constants determined by calibration [11], [30].…”

Section: Micro-raman Thermometry In Gan Hemtsmentioning

confidence: 99%

“…The earliest reports of micro-Raman thermography in GaN HEMTs utilized an empirical formula fitted to experimental data to relate the Stokes line position to the GaN temperature [2], [11]. Over time, it has been recognized that the inverse piezoelectric (IPE) and thermoelastic effects may also change the Stokes line position when a GaN HEMT is biased in the ON state, which needs to be accounted for in order to accurately measure the device temperature [4], [7]- [9], [12].…”

Section: Introductionmentioning

confidence: 99%

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Contributed Review: Experimental characterization of inverse piezoelectric strain in GaN HEMTs via micro-Raman spectroscopy

Bagnall

Wang

2016

Review of Scientific Instruments

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Micro-Raman thermography is one of the most popular techniques for measuring local temperature rise in gallium nitride (GaN) high electron mobility transistors (HEMTs) with high spatial and temporal resolution. However, accurate temperature measurements based on changes in the Stokes peak positions of the GaN epitaxial layers requires properly accounting for the stress and/or strain induced by the inverse piezoelectric effect. It is common practice to use the pinched OFF state as the unpowered reference for temperature measurements because the vertical electric field in the GaN buffer that induces inverse piezoelectric stress/strain is relatively independent of the gate bias. Although this approach has yielded temperature measurements that agree with those derived from the Stokes/anti-Stokes ratio and thermal models, there has been significant difficulty in quantifying the mechanical state of the GaN buffer in the pinched OFF state from changes in the Raman spectra. In this paper, we review the experimental technique of micro-Raman thermography and derive expressions for the detailed dependence of the Raman peak positions on strain, stress, and electric field components in wurtzite GaN. We also use a combination of semiconductor device modeling and electro-mechanical modeling to predict the stress and strain induced by the inverse piezoelectric effect. Based on the insights gained from our electromechanical model and the best values of material properties in the literature, we analyze changes in the E2 high and A1 (LO) Raman peaks and demonstrate that there are major quantitative discrepancies between measured and modeled values of inverse piezoelectric stress and strain. We examine many of the hypotheses offered in the literature for these discrepancies but conclude that 2 none of them satisfactorily resolves these discrepancies. Further research is needed to determine whether the electric field along the -axis could be affecting the phonon frequencies apart from the inverse piezoelectric effect in wurtzite GaN, which has been predicted theoretically in zinc blende gallium arsenide (GaAs).

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“…On the other hand, from the quantum mechanical point of view, the temperature-induced relative Raman redshift can be fitted to a negative Bose-Einstein population, 36,37 or equivalently: 38 -40 …”

Section: Temperature-induced Raman Redshiftmentioning

confidence: 99%

Atomistic origin and temperature dependence of Raman optical redshift in nanostructures: a broken bond rule

Pan

Tay

et al. 2007

J Raman Spectroscopy

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Consistent insight is presented into the atomistic origin and temperature (T) dependence of the redshift of Raman optical modes in nanostructures from INTRODUCTIONThe vibration of under-coordinated atoms at a surface and in a nanosolid is of great importance because the behavior of surface phonons influences directly the electrical, optical, and dielectric properties in semiconductor materials and devices, such as electron-phonon coupling, photoabsorption, and photoemission, as well as phonon scattering in the transport dynamics of electrons, phonons, and photons in devices. 1 -5 With miniaturization of a solid down to nanometer scales, the optical Raman modes shift toward lower wavenumbers. 6 On the other hand, when the temperature is increased, the Raman peaks also shift down to low wavenumbers monotonically yet nonlinearly at low temperatures. 7 -9 It is expected that the magnitude of vibration for a surface atom is always greater than that in the bulk. 10,11 However, the underlying mechanisms behind the size-and temperatureinduced Raman redshift of the optical modes remain ambiguous.Ł Correspondence to: Chang Q. Sun, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798, Singapore. E-mail: ecqsun@ntu.edu.sg Size-induced Raman redshiftThe size-induced redshift of Raman optical modes has usually been suggested to be activated by surface disorder, 12 surface stress, 13 -15 quantum confinement, 16 -19 local heating effects, 20 -22 or surface chemical passivation. The Raman shifts of TiO 2 particles are attributed to the effects of decreasing particle size on the force constants and the amplitudes of vibration of the nearest atomic neighbors. 23 However, the effect of stress can usually be ignored for hydrogenated silicon, 24,25 in which hydrogen atoms terminate the surface dangling bonds, which reduce the bond strains and hence the residual stress. The phonon quantum confinement argument 16 attributes the redshift of the asymmetric Raman line to the relaxation of the q-vector selection rule for the excitation of the Raman active phonons due to their localization. The relaxation of the momentum conservation rule arises from the finite crystalline size and the distribution of the diameters of the nanosolid in the films. When the size is decreased, the rule of momentum conservation will be relaxed and the Raman active modes will not be limited to the center of the Brillouin zone. 13 However, Alim et al. 21,22 who have measured resonant and nonresonant Raman scattering spectra for ZnO nanocrystals with an average diameter of 20 nm, proposed that the observed phonon redshift can be attributed to the local heating effects instead of phonon Atomistic origin and temperature dependence of Raman redshift in nanostructures 781 confinement effects. A Gaussian-type phonon confinement model 17 that has been used to fit the experimental data indicates that strong phonon damping is present, whereas calculations 26 using the correlation functions of the local dielectric constant...

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Temperature dependence of Raman scattering in single crystal GaN films

Cited by 155 publications

References 16 publications

Temperature dependence of Raman scattering in β-(AlGa)2O3 thin films

Temperature dependence of Raman scattering in β-(AlGa)2O3 thin films

Contributed Review: Experimental characterization of inverse piezoelectric strain in GaN HEMTs via micro-Raman spectroscopy

Atomistic origin and temperature dependence of Raman optical redshift in nanostructures: a broken bond rule

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