Optical Properties of Germanium Doped Cubic GaN

Journal of Applied Physics

Gerlach

Shvarkov

et al. 2019

We present a study of germanium as an alternative to silicon for n-type doping of cubic GaN. We find that Ge is a well-suited donor impurity. Our layers were grown by plasma-assisted molecular beam epitaxy on 3C-SiC/Si (001) substrates. Germanium-doped layers were fabricated with donor concentrations ranging over several orders of magnitude up to 3.7 × 10 20 cm −3 . For comparison, silicon-doped layers with donor concentrations of up to 3.8 × 10 19 cm −3 were also grown. Incorporation of germanium into the cubic GaN layers was verified by time-of-flight secondary ion mass spectrometry. The crystalline quality of our layers was analyzed using high-resolution x-ray diffraction. Germanium-as well as silicon-doped layers with donor concentrations above 10 19 cm −3 exhibited an increase of the dislocation density with increasing dopant concentration. The surface topography of our layers was investigated by atomic force microscopy. Comparable values for the surface roughness were measured for germanium-as well as silicon-doped layers. Optical properties were investigated by photoluminescence spectroscopy at 13 K. Doping with silicon resulted in a spectrally slightly narrower luminescence than doping with germanium. Donor concentrations and carrier mobilities were determined by Hall effect measurements at room temperature and we observe 20% higher electron mobilities for Ge-doping compared to Si-doping in the case of high dopant concentrations.Published under license by AIP Publishing. https://doi.

Section: Introductionmentioning

confidence: 99%

Germanium doping of cubic GaN grown by molecular beam epitaxy

Journal of Applied Physics

Gerlach

Shvarkov

et al. 2019

“…Furthermore, the intensity of the (D 0 ,A 0 ) transition becomes more intense in relation to (D 0 ,X). While the energy of the (D 0 ,X) transition remains unchanged (indicated by the dashed line), the (D 0 ,A 0 ) peak shifts by 52 meV to 3.189 eV due to Coulomb interaction between donors and acceptors . The Coulomb interaction energy is given by

Δ E = \frac{e^{2}}{4 π ε_{0} ε_{normalr} r}

where ε r = 9.44 is the relative permittivity of c‐GaN and r the mean distance from acceptors to donors

r = \sqrt[3]{\frac{3}{4 π N_{Ge}}}

…”

Section: Resultsmentioning

confidence: 99%

“…Growing the metastable cubic zinc blende phase is one way to overcome this effect as these fields are not present here . The most common donor for cubic GaN (c‐GaN) is Si, but recently, we have introduced Ge as an alternative n‐type dopant for c‐GaN …”

Section: Introductionmentioning

confidence: 99%

Molecular Beam Epitaxy Growth and Characterization of Germanium‐Doped Cubic Al_xGa₁₋_xN

Physica Status Solidi (b)

Henksmeier

Gerlach

et al. 2019

Self Cite

In cubic (c‐)GaN Ge has emerged as a promising alternative to Si for n‐type doping, offering the advantage of slightly improved electrical properties. Herein, a study on Ge doping of the ternary alloy c‐AlxGa1−xN is presented. Ge‐doped c‐AlxGa1−xN layers are grown by plasma‐assisted molecular beam epitaxy. In two sample series, both the Al mole fraction x and the doping level are varied. The incorporation of Ge is verified by time‐of‐flight secondary ion mass spectrometry. Ge incorporation and donor concentrations rise exponentially with increasing Ge cell temperature. A maximum donor concentration of 1.4 × 1020 cm−3 is achieved. While the incorporation of Ge is almost independent of x, incorporation of O, which acts as an unintentional donor, increases for higher x. Dislocation densities start increasing when doping levels of around 3 × 1019 cm−3 are exceeded. Also photoluminescence intensities begin to drop at these high doping levels. Optical emission of layers with x > 0.25 is found to originate from a defect level 0.9 eV below the indirect bandgap, which is not related to Ge. In the investigated range 0 ≤ x ≤ 0.6, Ge is a suitable donor in c‐AlxGa1−xN up to the low 1019 cm−3 range.

“…One unintentionally doped sample is present for reference. A description of the different dopants in c-GaN can be found elsewhere [34][35][36]. Important properties of the samples like layer thicknesses, source TABLE I.…”

Section: Methodsmentioning

confidence: 99%

Influence of the free-electron concentration on the optical properties of zincblende GaN up to 1×1020cm−3

Baron

Goldhahn

et al. 2019

Phys. Rev. Materials

Self Cite

We analyze the optical properties of zincblende gallium-nitride in the infrared and ultraviolet spectral range (≈27 meV-6.5 eV) experimentally by spectroscopic ellipsometry and provide a quantitative description of these results by k • p perturbation theory. Free-electron concentrations above 10 20 cm −3 are achieved by introducing germanium as a donor. We determine the dielectric function as well as band filling effects like the Burstein-Moss shift and band gap renormalization. The Kane model for the band structure of semiconductors near the-point allows to calculate the effective electron mass and to determine the nonparabolicity of the conduction band. At the same time, these results can be used to derive the free-electron concentration all-optically. The combination of Kane's model, Burstein-Moss shift, and band-gap renormalization can be used to expertly describe the measured transition energies up to ≈3.7 eV dependent on the carrier concentration, yielding an averaged hole mass of ≈0.61 m e for the contributing valence bands.