The structure of InAlGaN layers grown by metal organic vapour phase epitaxy: effects of threading dislocations and inversion domains from the GaN template

Abstract

SummaryDefects in quaternary InAlGaN barriers and their effects on crystalline quality and surface morphology have been studied. In addition to growth conditions, the quality of the GaN template may play an important role in the formation of defects in the barrier. Therefore, this work is focused on effects caused by threading dislocations (TDs) and inversion domains (IDs) originating from the underlying GaN. The effects are observed on the crystalline quality of the barrier and characteristic surface morphologies. Each type of TDs is shown to affect the surface morphology in a different way. Depending on the size of the corresponding hillock for a given pinhole, it was possible to determine the dislocation type. It is pointed out that the smallest pinholes are not connected to TDs whereas the large ones terminate either mixed type or edge type TDs. At sufficiently large layer thickness, the IDs originating from the GaN template lead to the formation of concentric trenches at the layer surface, and this is related to the change in growth kinetics on top and at the immediate surroundings of the ID.

The critical role of N-vacancy on chemical composition fluctuations and degradation of InAlN layer

“…Indeed, most of the layers are grown on top of GaN templates which are deposited on sapphire 16.17 , silicon 18 or SiC 19 and they contain high densities of crystallographic defects such as threading dislocations 20 , inversion domains 21 and stacking faults 22.23 . These defects are transmitted into the growing alloy and may generate typical crystallographic degradations 24 . Other authors have proposed that there could be a critical thickness beyond which the alloy undergoes strain relaxation through crystallographic degradation and generation of extended defects 10 .…”

The effect of N-vacancy and In aggregation on the properties of InAlN

“…In our current investigations and by carefully examining the results of the literature, we became convinced that probably the coalescence of growth hillocks is not the most predominant origin of the V-defects, as they start to form on the tops of hillock, and not between [14]. Moreover, each crystallographic defect can influence in a typical way the observed degradation of the InAlN/GaN layers [15] and it is not clear that even for the spontaneous degradation, a critical thickness can be accurately determined [16]. As reported more recently, this degradation may also be related to local indium segregation which has been shown to be favorable when relaxing the strain which is introduced in the system by N-vacancies [16].…”

“…This of course is due to the electronegativity difference between Al and N. 6 If now V N is introduced in the middle of the AlN bulk supercell, the 0.73 ELF isosurface allows to clearly visualize the asymmetry in the electron density around the vacancy. In this area, the ELF within the structure viewed along the [11][12][13][14][15][16][17][18][19][20] . The charge density is highest at the barycenter of these three Al atoms, and equally spread towards each of them.…”

“…ELF 0.73 isosurface for the structure viewed along[11][12][13][14][15][16][17][18][19][20], the yellow features mark the high electron densityareas and the V N position is shown by the black asterisk *, the Al atoms underlined with a yellow cross are those around the V N . As can be seen in figure 4, the 2D ELF contour of AlN underlines the location of the highest density as seen inside the (0001) plane around V N .…”

Effect of InGaN Channel on Radio‐Frequency Performance in High‐Electron‐Mobility Transistors with an InAlGaN Barrier

“…[6] The quaternary AlInGaN alloy barrier can enhance its miscibility [7] and provide an additional degree of freedom to individually regulate energy bandgaps and stress states through the addition of Ga, [8,9] which is also expected to minimize the gate-to-channel distance at high-saturation current density. [10,11] To work at higher frequencies, the gate length in the conventional AlGaN/GaN HEMTs should be significantly scaled down. [12] However, the thickness of the AlGaN barrier cannot be further reduced by decreasing the gate length, [6] otherwise significantly reducing the saturation drain current density of the device.…”