Ge doping of GaN beyond the Mott transition

Ajay, Akhil; Schörmann, Jörg; Jimenez-Rodriguez, M.; Lim, C. B.; Walther, Felix; Rohnke, Marcus; Mouton, Isabelle; Amichi, Lynda; Bougerol, Catherine; Hertog, Martien I. den; Eickhoff, Martin; Monroy, E.

doi:10.1088/0022-3727/49/44/445301

Cited by 43 publications

(48 citation statements)

References 36 publications

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“…Despite the high free-electron concentration achieved by these techniques, the minimum resistivity of the GaN films remains high (0.3-0.4 mΩ cm) at electron concentrations of ∼2 × 10 20 cm 3 , 2,3 and the resistivity increases with increasing dopant concentration. 3,5 This behavior is likely caused by a decrease in the electron mobility due to diminished doping efficiency and/or by a degradation in material quality; in either case, this behavior prevents us from understanding the intrinsic electron transport properties of degenerate GaN. Hence, the development of a growth technique that offers high electron mobility as well as high carrier density should be highly sought after.…”

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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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confidence: 99%

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

et al. 2017

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“…The strain that remains after growth is around εxx = 0.12±0.04% (see ref. [1] for a statistical analysis) and increases with the Al mole fraction of the layers, as illustrated in Fig. 2(a To gain further insight on the nature of such Ge-rich areas, EDS/SEM studies of the samples with the highest Ge concentration have been performed.…”

Section: Resultsmentioning

confidence: 99%

“…Although silicon has long been the preferred n-type dopant for AlGaN, germanium is currently under consideration, particularly in those applications that require dopant concentrations around or higher than 10 19 cm −3 [1][2][3][4]. In the case of AlGaN planar layers, high Si doping levels contribute to edge-type dislocation climb and induce tensile stress [4][5][6][7], which leads to a degradation of the surface morphology and favors crack propagation.…”

Section: Introductionmentioning

confidence: 99%

Electrical and optical properties of heavily Ge-doped AlGaN

Blasco¹,

Ajay²,

Robin³

et al. 2019

J. Phys. D: Appl. Phys.

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We report the effect of germanium as n-type dopant on the electrical and optical properties of AlxGa1-xN layers grown by plasma-assisted molecular-beam epitaxy. The Al content has been varied from x = 0 to 0.66, confirmed by Rutherford backscattering spectrometry, and the Ge concentration was increased up to [Ge] = 1×10 21 cm −3 . Even at these high doping levels (> 1% atomic fraction) Ge does not induce any structural degradation in AlxGa1-xN layers with x < 0.15. However, for higher Al compositions, clustering of Ge forming crystallites were observed. Hall effect measurements show a gradual decrease of the carrier concentration when increasing the Al mole fraction, which is already noticeable in samples with x = 0.24. Samples with x = 0.64-0.66 remain conductive (σ = 0.8-0.3 Ω −1 cm −1 ), but the donor activation rate drops to around 0.1% (carrier concentration around 1×10 18 cm −3 for [Ge] ≈ 1×10 21 cm −3 ). From the optical point of view, the low temperature photoluminescence is dominated by the band-to-band

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“…This result was attributed to the replacement of Si doping by Ge [11]. In planar layers, Ge has demonstrated the possibility of obtaining high dopant concentrations, above the Mott density (10 À19 cm À3 ), without surface roughening or crack propagation [12][13][14].…”

Section: The Three-dimensional Confinement Of Carriers In Nwmentioning

confidence: 99%

“…This result was attributed to the replacement of Si doping by Ge . In planar layers, Ge has demonstrated the possibility of obtaining high dopant concentrations, above the Mott density (10 −19 cm −3 ), without surface roughening or crack propagation . Recently the conductivity studies in NWs , and observation of screening of the internal electric fields due to Ge incorporation in NW heterostructures have been demonstrated .…”

Section: Introductionmentioning

confidence: 99%