Nitride Semiconductors Investigated at a Nanoscale
The present review deals with two important issues that inhibited a rapid development of III-nitrides devices. Namely; p-type doping of GaN and GaN quantum dots on dislocations free surfaces. The first issue was governed by an auto-compensation phenomenon that limited high p-type doping, while the second was affected by threading dislocations that would act as trap centers for carriers preventing an efficient electrical injection. In both cases, the overall electronic behavior is essentially governed both by the intrinsic structure, strain-state and chemistry of these nanoscopic objects, in addition to the nature of interfaces therein. Transmission electron microscopy (TEM) was extensively used to provide local atomic imaging, electron diffraction and spectroscopy with high spatial-resolution and energy-resolution offering therefore numerous possibilities for locally investigating and characterizing the electronic, optical, chemical, and structural properties. This review starts with a brief introduction to basic properties of III-nitride semiconductors, with a description of growth techniques used for the elaboration of studied samples and followed by a recall of electron microscopy and its associated techniques. Particular attention is then paid to detailed investigations regarding p-type doped GaN samples grown with metalorganic vapor phase deposition and GaN QDs grown using molecular beam epitaxy. These results are presented in two separate chapters. A conclusion summarizing main points and a look towards the future is made at the end.
KeywordsIII-nitrides GaN p-type quantum dots epitaxy HRTEM EELS dislocation strain-state nano-analysis
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