研究目的
Investigating the effect of germanium as an n-type dopant on the electrical and optical properties of AlxGa1-xN layers, including structural impacts, carrier concentration, and donor activation rates.
研究成果
Ge doping in AlGaN does not cause structural degradation for x < 0.15 but leads to clustering and reduced carrier concentration at higher Al contents. The donor activation rate drops significantly, and optical properties are dominated by band-to-band emission with efficient screening of alloy disorder by free carriers. This suggests limitations for Ge as a dopant in high-Al-content AlGaN, necessitating alternative approaches for high conductivity.
研究不足
The study is limited to AlGaN layers with Al mole fractions up to 0.66; higher compositions may show different behaviors. Ge clustering occurs at high Al contents, reducing dopant effectiveness. Detection limits for Ge concentration are around 10^21 cm^-3 for PIXE and 5×10^18 to 10^19 cm^-3 for SIMS/APT, potentially missing lower concentrations. High-resistance samples hindered reliable Hall measurements for x=0.66.
1：Experimental Design and Method Selection:
The study involved growing Ge-doped AlxGa1-xN layers with varying Al and Ge concentrations using plasma-assisted molecular-beam epitaxy (PAMBE) to analyze electrical and optical properties. Theoretical models for donor activation and photoluminescence quenching were applied.
2：Sample Selection and Data Sources:
Samples were grown on AlN-on-sapphire templates with Al mole fractions from 0 to 0.66 and Ge concentrations from 10^19 to 10^21 cm^-3. Data were obtained from RBS, PIXE, SIMS, EDS, APT, XRD, Hall effect, and PL measurements.
3：66 and Ge concentrations from 10^19 to 10^21 cm^-Data were obtained from RBS, PIXE, SIMS, EDS, APT, XRD, Hall effect, and PL measurements. List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: Equipment included a PAMBE system, RBS with 1.8 MeV 4He+ ion beam, PIXE with 2 MeV proton beam, SEM with EDS detector, APT system (CAMECA Flextap), XRD (Rigaku SmartLab), Hall effect setup with Van der Paw configuration, and PL setup with 488 nm laser and monochromator. Materials included Al, Ga, Ge sources, and AlN templates.
4：8 MeV 4He+ ion beam, PIXE with 2 MeV proton beam, SEM with EDS detector, APT system (CAMECA Flextap), XRD (Rigaku SmartLab), Hall effect setup with Van der Paw configuration, and PL setup with 488 nm laser and monochromator. Materials included Al, Ga, Ge sources, and AlN templates. Experimental Procedures and Operational Workflow:
4. Experimental Procedures and Operational Workflow: Layers were grown under metal-rich conditions at 710-720°C. Ge cell temperatures were varied to control doping. Characterization involved RBS for composition, PIXE/EDS for elemental mapping, APT for atomic distribution, XRD for structural analysis, Hall effect for electrical properties, and PL for optical properties at low temperatures.
5：Data Analysis Methods:
Data were analyzed using NDF code for RBS, OMDAQ for PIXE, fitting equations for PL intensity and energy shifts, and standard models for carrier concentration and resistivity.
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energy dispersive x-ray spectroscopy detector
EDS
Bruker
Chemical analysis and mapping
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x-ray diffractometer
SmartLab
Rigaku
Structural quality analysis via XRD
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plasma-assisted molecular-beam epitaxy system
PAMBE
Growth of Ge-doped AlGaN layers
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Rutherford backscattering spectrometry system
RBS
Measurement of Al content and thickness in layers
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particle induced x-ray emission system
PIXE
Elemental mapping and Ge concentration analysis
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secondary ion mass spectrometry system
SIMS
Validation of Ge concentration
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atom probe tomography system
Flextap
CAMECA
Three-dimensional atomic distribution analysis
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Hall effect measurement system
Electrical property measurement
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photoluminescence setup
Jobin Yvon
Optical property measurement via PL
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