M. Nouf-Allehiani

Spatial clustering of defect luminescence centers in Si-doped low resistivity Al0.82Ga0.18N

A series of Si-doped AlN-rich AlGaN layers with low resistivities was characterized by a combination of nanoscale imaging techniques. Utilizing the capability of scanning electron microscopy to reliably investigate the same sample area with different techniques, it was possible to determine the effect of doping concentration, defect distribution, and morphology on the luminescence properties of these layers. Cathodoluminescence shows that the dominant defect luminescence depends on the Si-doping concentration. For lower doped samples, the most intense peak was centered between 3.36 eV and 3.39 eV, while an additional, stronger peak appears at 3 eV for the highest doped sample. These peaks were attributed to the (VIII-ON)2− complex and the VIII3− vacancy, respectively. Multimode imaging using cathodoluminescence, secondary electrons, electron channeling contrast, and atomic force microscopy demonstrates that the luminescence intensity of these peaks is not homogeneously distributed but shows a strong dependence on the topography and on the distribution of screw dislocations.

High-Resolution Electron Backscatter Diffraction in III-Nitride Semiconductors

The large and increasing interest in III-nitrides semiconductors lies in the wide range of useful applications that can be achieved, from high electron mobility transistors (HEMTs) to light emitting LEDs and lasers. However, the III-nitride materials are usually epitaxially grown on foreign substrates, which lead to the formation of a large number of dislocations and significant strain variations in the epitaxial layers that seriously affect the performance of devices based upon them.

Non-destructive Imaging of Extend Defects in III-nitride Thin film Structures Using Electron Channelling Contrast Imaging

Irrespective of the substrates, the growth plane, or the growth conditions employed, extended defects such as threading dislocations, stacking faults, misfit dislocations and grain boundaries are generally observed in the as–grown III-nitride thin film structures. Often extended defects are electrically active and are problematic for minority carrier devices, such as AlGaN based ultraviolet light emitting diodes and high electron mobility transistors. This is why structural characterisation techniques which are simultaneously rapid to use, and structurally definitive on the nanoscale become a prerequisite. Electron channelling contrast imaging (ECCI) performed in a scanning electron microscope (SEM) is a quick and non-destructive structural characterisation technique for imaging, identifying and quantifying extended defects in nitride thin films [1, 2].