研究目的
Investigating the doping of Gallium nitride (GaN) with elemental Germanium (Ge) grown by ammonia molecular beam epitaxy to achieve high n++ doping for contact layers and tunnel junctions in devices.
研究成果
The study successfully demonstrated high n++ doping of GaN films with Ge using ammonia molecular beam epitaxy, achieving carrier concentrations greater than 2x1020 cm-3 and resistivities below 3x10-4 Ω?cm. The optimal growth temperature was found to be 740 °C, with higher temperatures leading to compensation effects. Despite morphological degradation at high doping levels, thin layers of highly doped films are promising for applications in tunnel junctions and ohmic contact layers.
研究不足
The study is limited by the onset of morphological degradation and the formation of compensating defects at high doping concentrations, which affect the electrical and optical properties of the films. Additionally, the optimal growth conditions are narrow, requiring precise control over the substrate temperature and Ge flux.
1：Experimental Design and Method Selection:
The study involved growing GaN films doped with Ge using ammonia molecular beam epitaxy, varying parameters such as GaN growth rate, substrate growth temperature, and Ge flux.
2：Sample Selection and Data Sources:
Homoepitaxial growth was performed on commercially purchased 2-inch, Fe-doped, semi-insulating GaN templates nucleated on sapphire by MOCVD.
3：List of Experimental Equipment and Materials:
A Veeco 930 MBE system with a custom ammonia shower head injector for NH3-MBE growth was used. The Ga flux was provided with a dual zone standard effusion cell, while the Ge flux was provided with a single zone dopant effusion cell.
4：Experimental Procedures and Operational Workflow:
The substrate temperature was monitored by optical pyrometry calibrated to 500 nm of Titanium (Ti) deposited on the backside of the samples. Secondary Ion Mass Spectroscopy (SIMS), transmission electron microscopy (TEM), photo-luminescence (PL) measurements, and Hall effect measurements were conducted.
5：Data Analysis Methods:
The data was analyzed to understand the incorporation dependencies of Ge in GaN films and their electrical and optical properties.
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