Effect of dislocations on thermal conductivity of GaN layers

Kotchetkov, D.; Zou, Jiao; Balandin, Alexander A.; Florescu, D. I.; Pollak, Fred H.

doi:10.1063/1.1427153

Cited by 129 publications

(80 citation statements)

References 14 publications

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“…These terms are shown in previous work to represent the dominant scattering mechanisms in III-nitride materials. 4,[26][27][28][29] It is important to note that the RTA is valid only for elastic and isotropic scattering. In particular, of the scattering mechanisms used in this work, polar optical phonon scattering violates this assumption.…”

Section: Electron Transport Modelmentioning

confidence: 99%

Calculated thermoelectric properties of InxGa1−xN, InxAl1−xN, and AlxGa1−xN

Sztein

Haberstroh

Bowers

et al. 2013

Journal of Applied Physics

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The thermoelectric properties of III-nitride materials are of interest due to their potential use for high temperature power generation applications and the increasing commercial importance of the material system; however, the very large parameter space of different alloy compositions, carrier densities, and range of operating temperatures makes a complete experimental exploration of this material system difficult. In order to predict thermoelectric performances and identify the most promising compositions and carrier densities, the thermoelectric properties of InxGa1−xN, InxAl1−xN, and AlxGa1−xN are modeled. The Boltzmann transport equation is used to calculate the Seebeck coefficient, electrical conductivity, and the electron component of thermal conductivity. Scattering mechanisms considered for electronic properties include ionized impurity, alloy potential, polar optical phonon, deformation potential, piezoelectric, and charged dislocation scattering. The Callaway model is used to calculate the phonon component of thermal conductivity with Normal, Umklapp, mass defect, and dislocation scattering mechanisms included. Thermal and electrical results are combined to calculate ZT values. InxGa1−xN is identified as the most promising of the three ternary alloys investigated, with a calculated ZT of 0.85 at 1200 K for In0.1Ga0.9N at an optimized carrier density. AlxGa1−xN is predicted to have a ZT of 0.57 at 1200 K under optimized composition and carrier density. InxAl1−xN is predicted to have a ZT of 0.33 at 1200 K at optimized composition and carrier density. Calculated Seebeck coefficients, electrical conductivities, thermal conductivities, and ZTs are compared with experimental data where such data are available.

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Section: Electron Transport Modelmentioning

confidence: 99%

Calculated thermoelectric properties of InxGa1−xN, InxAl1−xN, and AlxGa1−xN

Sztein

Haberstroh

Bowers

et al. 2013

Journal of Applied Physics

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“…We note, as in Mion et al, that earlier models for relaxation time tend to predict a lesser reduction in the thermal conductivity of GaN due to dislocations. 24,29,30 The TC Model with the additional s D term has been applied to our GaN film with a dislocation density of 1.2 Â 10 8 cm À2 . This dislocation density was measured using the KOH etchant method described earlier.…”

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confidence: 99%

Layer-by-layer thermal conductivities of the Group III nitride films in blue/green light emitting diodes

Huang

Liu

et al. 2012

Applied Physics Letters

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Thermal conductivities (k) of the individual layers of a GaN-based light emitting diode (LED) were measured along [0001] using the 3-omega method from 100-400 K. Base layers of AlN, GaN, and InGaN, grown by organometallic vapor phase epitaxy on SiC, have effective k much lower than bulk values. The 100 nm thick AlN layer has k ¼ 0.93 6 0.16 W/mK at 300 K, which is suppressed >100 times relative to bulk AlN. Transmission electron microscope images revealed high dislocation densities (4 Â 10 10 cm À2 ) within AlN and a severely defective AlN-SiC interface that cause additional phonon scattering. Resultant thermal resistances degrade LED performance and lifetime making layer-by-layer k, a critical design metric for LEDs. More than 20% of electricity in the United States is consumed by lighting. Solid-state light emitting diodes (LEDs) hold considerable potential to be more efficient and effective sources of artificial light than incandescent and fluorescent technologies. 1 Group III nitride-based blue and green LEDs are currently being developed for this purpose. Device architectures consist of light-emitting multiple quantum wells (MQWs) supported by base layers of aluminum nitride (AlN), gallium nitride (GaN), and indium gallium nitride (InGaN). The MQW itself is a periodic structure composed of alternating InGaN wells and GaN barriers.Heat generation and removal in the LED are complicated by multiple interfaces, causing high operating temperatures that degrade efficiency, shift the emission spectrum, and reduce the lifetime of LEDs. 2 Prior experimental investigations of bulk GaN and AlN have shown that thermal transport is phonon-dominated. [3][4][5][6] Previous thin film studies have been (i) based on ideal films with low defect concentrations that are unrepresentative of LED grade films 3,7 or (ii) focused on high electron mobility transistors (HEMTs), rather than LED architectures. [8][9][10] Neither submicron GaN films nor real nitride based LED devices have been investigated.Studies of Si and other thin films have demonstrated that thermal conductivity is greatly reduced when the thickness of the film or the defect spacing is less than the intrinsic mean free path of the phonons. 5,11,12 Nitride based LED structures are fabricated from multiple layers of thin films ranging from 3 nm to 100 nm in thickness; whereas, the spectrum-average phonon mean free path in GaN at 300 K is $100 nm, 13 and the longest phonon mean free paths in the spectrum are much greater. 14 To achieve economic viability, the nitride films are grown by organometallic vapor phase epitaxy (OMVPE) on foreign substrates, including SiC, sapphire, and Si. Mismatched lattice constants at the filmsubstrate interface create high densities of atomic and line defects, the latter of which that extend throughout the device as a source of phonon scattering. Given these considerations, this paper reports layer-by-layer experimental measurements of thermal conductivity in real nitride based LED architectures grown on [0001]-oriented SiC substrates. Th...

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“…This high In/N mass ratio also implies a high sensitivity of its thermal conductivity to In-related point defects [8]. The performance of InN devices is reliable but affected by the self-heating [9]. The cause of self-heating is poor removal of heat from the active region of the device.…”

Section: Introductionmentioning

confidence: 98%

Effect of built-in-polarization field on intrinsic and extrinsic thermal conductivity of InN

2015

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The effect of built-in-polarization field on intrinsic and extrinsic lattice thermal conductivity of InN has been investigated theoretically. The built-in-polarization field modifies elastic constant, phonon velocity and Debye temperature of InN. Using these modified parameters, the relaxation time of phonons in various scattering processes at room temperature has been computed as a function of phonon frequency for with and without built-in-polarization field. The result shows that built-in-polarization field enhances the relaxation time of phonons. This implies longer mean free path of phonons. The Callaway model of phonon thermal conductivity has been used to estimate the effect of built-in-polarization field on intrinsic and extrinsic thermal conductivity of InN. The theoretical analysis shows that up to a certain temperature, the polarization field acts as negative effect and reduces the intrinsic and extrinsic thermal conductivity. However, after this temperature, both thermal conductivity are significantly contributed by polarization field. This gives the idea of temperature dependence of polarization effect, which signifies pyro-electric character of InN. The intrinsic thermal conductivity of InN at room temperature including built-in-polarization field is found to be enhanced by 28 %. However, at room temperature, the extrinsic thermal conductivity with built-in-polarization mechanism is found to be enhanced by 15 %. The method, we have developed may be taken in the simulation of heat transport in optoelectronic nitride devices to minimize the self-heating processes and in polarization engineering strategies to optimize the thermoelectric performance of InN alloys.

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Effect of dislocations on thermal conductivity of GaN layers

Cited by 129 publications

References 14 publications

Calculated thermoelectric properties of InxGa1−xN, InxAl1−xN, and AlxGa1−xN

Calculated thermoelectric properties of InxGa1−xN, InxAl1−xN, and AlxGa1−xN

Layer-by-layer thermal conductivities of the Group III nitride films in blue/green light emitting diodes

Effect of built-in-polarization field on intrinsic and extrinsic thermal conductivity of InN

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