| Summary: | 碩士 === 長庚大學 === 光電工程研究所 === 94 === In recent years, In-rich InxGa1-xN layers have been widely studied for the application of solar cell, double-heterojunction bipolar transistor and laser diodes. The large difference in growth temperature of InN and GaN presents a great challenge to the epitaxy of In-rich InGaN. In addition, phase separation is another concern when the indium composition is higher than 6%. The background carrier concentration is high for the un-doped InxGa1-xN layers, making it difficult to dope Mg. Much less research is reported for the p-type In-rich InxGa1-xN. The high indium composition of p-type InxGa1-xN layers could enhance the hole concentration by reducing the acceptor activation energy. This would make easy the fabrication of p-type ohmic electrode.
In this work, two groups of Mg-doped In-rich InxGa1-xN layers were grown on sapphire by metal-organic vapor phase epitaxy (MOVPE). One group was grown at a constant temperature while the other one at changing temperatures. Both groups contained InxGa1-xN with x= 0, 0.2, 0.4, 0.6, 0.8 and 1.0. The SIMS result showed the Mg concentration varying between ~1×1019 and ~4×1019 cm-3. The samples were annealed around 600~700℃ in a nitrogen environment.
The material composition and the film quality were examined by X-ray diffraction, atomic force microscopy and scanning electron microscopy. The photoluminescence spectra showed the optical properties relating to Mg doping. The Hall measurement results showed the hole concentration (5~10×1018 cm-3) of in the Mg-doped In-rich In0.56Ga0.32N layers, higher than that the Mg-doped GaN layers (1×1017 cm-3). The mobility varied from 1 to 10 cm2/Vs. The hole concentration also increased with increasing indium composition in the InGaN grown. Our work has thus produced p-InGaN with the highest known In content. The root-mean-square of the surface roughness of the Mg-doped InxGa1-xN layers decreased with increasing gallium composition.
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