Anisotropy of effective electron masses in highly doped nonpolar GaN

Feneberg, Martin; Lange, Karsten; Lidig, Christian; Wieneke, Matthias; Witte, Hartmut; Bläsing, J.; Dadgar, A.; Krost, A.; Goldhahn, R.

doi:10.1063/1.4840055

Cited by 33 publications

(26 citation statements)

References 14 publications

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“…50 An isotropic electron effective mass of m e = 0.23m o was used, where m o is the free electron mass. 51 The electron-acoustic phonon deformation potential was taken as E 1 = 9.1 eV. 52 To test the model and the fitting procedure we first analyze the thermal conductivity data reported by Slack et al 7 using the steady-state heat flow method for an undoped free-standing GaN sample grown by HVPE.…”

Section: Resultsmentioning

confidence: 99%

Effect of Si doping on the thermal conductivity of bulk GaN at elevated temperatures – theory and experiment

et al. 2017

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The effect of Si doping on the thermal conductivity of bulk GaN was studied both theoretically and experimentally. The thermal conductivity of samples grown by Hydride Phase Vapor Epitaxy (HVPE) with Si concentration ranging from 1.6×1016 to 7×1018 cm-3 was measured at room temperature and above using the 3ω method. The room temperature thermal conductivity was found to decrease with increasing Si concentration. The highest value of 245±5 W/m.K measured for the undoped sample was consistent with the previously reported data for free-standing HVPE grown GaN. In all samples, the thermal conductivity decreased with increasing temperature. In our previous study, we found that the slope of the temperature dependence of the thermal conductivity gradually decreased with increasing Si doping. Additionally, at temperatures above 350 K the thermal conductivity in the highest doped sample (7×1018 cm-3) was higher than that of lower doped samples. In this work, a modified Callaway model adopted for n-type GaN at high temperatures was developed in order to explain such unusual behavior. The experimental data was analyzed with examination of the contributions of all relevant phonon scattering processes. A reasonable match between the measured and theoretically predicted thermal conductivity was obtained. It was found that in n-type GaN with low dislocation densities the phonon-free-electron scattering becomes an important resistive process at higher temperatures. At the highest free electron concentrations, the electronic thermal conductivity was suggested to play a role in addition to the lattice thermal conductivity and compete with the effect of the phonon-point-defect and phonon-free-electron scattering.

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Section: Resultsmentioning

confidence: 99%

Effect of Si doping on the thermal conductivity of bulk GaN at elevated temperatures – theory and experiment

et al. 2017

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“…Recent experimental reports have also revealed that the effective mass of degenerate wurtzite GaN can be expressed by a parabolic conduction band (α = 0) with an electron concentration as high as 1.2 × 10 20 cm 3 . 17 To improve the electron transport model of degenerate GaN with n(RT) > 1 × 10 20 cm 3 , we carefully performed temperature-dependent Hall-effect measurements. Figure 3(a) shows the temperature dependence of electron mobility for the Si-doped sample with n(RT) = 3.3 × 10 20 cm 3 .…”

Section: -mentioning

confidence: 99%

Electron transport properties of degenerate n-type GaN prepared by pulsed sputtering

et al. 2017

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We report a systematic investigation of the transport properties of highly degenerate electrons in Ge-doped and Si-doped GaN epilayers prepared using the pulsed sputtering deposition (PSD) technique. Secondary-ion mass spectrometry and Hall-effect measurements revealed that the doping efficiency of PSD n-type GaN is close to unity at electron concentrations as high as 5.1 × 1020 cm−3. A record low resistivity for n-type GaN of 0.16 mΩ cm was achieved with an electron mobility of 100 cm2 V−1 s−1 at a carrier concentration of 3.9 × 1020 cm−3. We explain this unusually high electron mobility of PSD n-type GaN within the framework of conventional scattering theory by modifying a parameter related to nonparabolicity of the conduction band. The Ge-doped GaN films show a slightly lower electron mobility compared with Si-doped films with the same carrier concentrations, which is likely a consequence of the formation of a small number of compensation centers. The excellent electrical properties presented in this letter clearly demonstrate the striking advantages of the low-temperature PSD technique for growing high-quality and highly conductive n-type GaN.

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“…a) and (b) describe the variation of carrier concentration and resistivity with temperature in samples with doping levels up to the density of the Mott transition (~1-1.5×1019 cm -3 in GaN at room temperature)[28,29]. The activation energies Ea extracted from figure 5(a) decrease from 19.5 meV for the lowest doped sample A, to 12.4 meV for sample B, and 9.7 meV for sample C, in accordance with the decrease in average distance between the impurity atoms[30].…”

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Ge doping of GaN beyond the Mott transition

Ajay¹,

Schörmann²,

Jimenez-Rodriguez³

et al. 2016

J. Phys. D: Appl. Phys.

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We present a study of germanium as n-type dopant in wurtzite GaN films grown by plasma-assisted molecular-beam epitaxy, reaching carrier concentrations of up to 6.7×10 20 cm -3 at 300 K, well beyond the Mott density. The Ge concentration and free carrier density were found to scale linearly with the Ge flux in the studied range. All the GaN:Ge layers present smooth surface morphology with atomic terraces, without trace of pits or cracks, and the mosaicity of the samples has no noticeable dependence on the Ge concentration. The variation of the GaN:Ge band gap with the carrier concentration is consistent with theoretical calculations of the band gap renormalization due to electronelectron and electron-ion interaction, and Burstein-Moss effect.

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Anisotropy of effective electron masses in highly doped nonpolar GaN

Cited by 33 publications

References 14 publications

Effect of Si doping on the thermal conductivity of bulk GaN at elevated temperatures – theory and experiment

Effect of Si doping on the thermal conductivity of bulk GaN at elevated temperatures – theory and experiment

Electron transport properties of degenerate n-type GaN prepared by pulsed sputtering

Ge doping of GaN beyond the Mott transition

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