Investigation for the Formation of Polarization-Induced Two-Dimensional Electron Gas in AlGaN/GaN Heterostructure Field Effect Transistors

The formation of two-dimensinal electron gas (2DEG) in AlGaN/GaN heterostructure field effect transistors was investigated using synchrotron radiation photoemission spectroscopy and high-resolution X-ray diffraction. The surface band bending, interfacial strain and 2DEG density were evaluated as a function of AlGaN barrier thickness and composition. The 2DEG density increased with the thickness, but the surface Fermi level was independent of the thickness of AlGaN layer. This suggested that the polarization-induced 2DEG originated from the AlGaN barrier, which is unintentionally doped due to the nonstoichiometry of nitrogen deficiency and donor-like impurities.