研究目的
To characterize the structure of the valence band maximum and deep-level defects in Mg-ion implanted GaN samples using photothermal de?ection spectroscopy, and to discuss the effects of thermal annealing on Urbach energy, defect levels, and photoluminescence, with a focus on understanding the activation of p-type conduction.
研究成果
The research demonstrates that thermal annealing improves structural disorder (reducing Urbach energy) and reduces defect levels in Mg-implanted GaN, leading to enhanced photoluminescence and signs of p-type conduction at higher temperatures. The improvement of Urbach energy is identified as crucial for p-type activation, rather than just reducing defect densities. PDS is validated as a useful technique for evaluating ion-implanted III-V nitrides.
研究不足
The study is limited to Mg-implanted GaN with specific implantation conditions and annealing temperatures. The PDS method may not provide absolute defect densities or precise defect level positions due to differences in matrix elements and quantum efficiency. The samples are not fully activated for p-type conduction, and the correlation with other characterization methods requires further comprehensive discussion.
1：Experimental Design and Method Selection:
The study uses photothermal de?ection spectroscopy (PDS) to evaluate structural disorder and defect levels in Mg-implanted GaN films. PDS is chosen for its ability to detect defect levels regardless of charge state and Fermi level position, and it is compared with positron annihilation spectroscopy (PAS) results. Hard x-ray photoemission spectroscopy (HAXPES) and photoluminescence-excitation (PLE) are also employed for valence band analysis and luminescence studies.
2：Sample Selection and Data Sources:
Samples are 8-μm-thick undoped GaN films grown by metalorganic vapor phase epitaxy (MOVPE) on (0001) bulk GaN substrates with dislocation density of 10^6 cm^-2. Mg+ ions are implanted to achieve a box profile with concentration of 4 × 10^19 cm^-3 at 500 °C, followed by annealing at temperatures from 1000 to 1300 °C in N2 atmosphere. Reference samples include HVPE-GaN bulk and Mg-doped GaN with p-conduction.
3：Mg+ ions are implanted to achieve a box profile with concentration of 4 × 10^19 cm^-3 at 500 °C, followed by annealing at temperatures from 1000 to 1300 °C in N2 atmosphere. Reference samples include HVPE-GaN bulk and Mg-doped GaN with p-conduction.
List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: Equipment includes a PDS system with an ozone-less Xe lamp (350–800 nm) as pumping source, a semiconductor laser (660 nm) as probe, hexane for enhancing deflection, HAXPES apparatus at SPring-8 BL15XU beamline (5.95 keV X-rays), and PLE setup with a 450 W Xenon lamp. Materials include GaN films, AlN encapsulation caps, and hexane.
4：95 keV X-rays), and PLE setup with a 450 W Xenon lamp. Materials include GaN films, AlN encapsulation caps, and hexane.
Experimental Procedures and Operational Workflow:
4. Experimental Procedures and Operational Workflow: After ion implantation and AlN cap deposition, samples are annealed, caps are removed, and PDS measurements are conducted at room temperature with chopping frequency of 11 Hz. HAXPES measurements are performed at SPring-8 with specific energy and geometry settings. PLE spectra are measured using lock-in detection.
5：Data Analysis Methods:
Urbach energy is estimated from the slope of PDS spectra between 3.3 eV and 3.15 eV. Integrated PDS areas and S-W parameters from PAS are analyzed. Valence band spectra are referenced to Fermi level of gold, and PLE signals are correlated with defect levels.
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