Phone þ33 2 31 45 26 63, Fax: þ33 2 31 45 25 57In this work, we have investigated the non-intentional incorporation of gallium in InAlN layers grown by metal organic vapor phase epitaxy (MOVPE) using two reactors. Atomic force microscopy (AFM) and electron dispersive X-ray spectroscopy (EDS) have been used to characterize the surface morphology and the atomic composition of InAl(Ga) N/GaN structures. The horizontal chamber systematical produces pure ternary layers whereas the close coupled shower head vertical chamber can lead to quaternary alloys. Cleaning the latter significantly reduces the amount of gallium to 1% in the epilayers. Moreover, we show an alternative way to reduce the amount gallium: the use of an intermediate growth pressure typically around 80 Torr drops the inclusion of gallium to 6%. In the presence of such amount of Ga, the growth process appears to be modified and there is a competition between In and Ga for their incorporation, and the Al composition is systematically reduced. The morphology of the layers is also observed to suffer, with the formation of large and closed trenches toward a possible three dimensional growth mode when the layer thickness is increased.

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.

Abstract:We report on the electron transport properties of two-dimensional electron gas confined in a quaternary barrier InAlGaN/AlN/GaN heterostructure down to cryogenic temperatures for the first time. A state-of-the-art electron mobility of 7340 cm 2¨V´1¨s´1 combined with a sheet carrier density of 1.93ˆ10 13 cm´2 leading to a remarkably low sheet resistance of 44 Ω/˝are measured at 4 K. A strong improvement of Direct current (DC) and Radio frequency (RF) characteristics is observed at low temperatures. The excellent current and power gain cutoff frequencies (f T /f max ) of 65/180 GHz and 95/265 GHz at room temperature and 77 K, respectively, using a 0.12 µm technology confirmed the outstanding 2DEG properties.

In this work, local electrical properties of the crystallographic defects including V‐defects and trenches in ternary alloy AlGaN and quaternary alloys Al(Ga,In)N with different indium concentration are studied by light‐assisted Kelvin probe force microscopy. This surface sensitive technique is used to reveal the role of these defects as deep level electron traps. The evolution of topography of the layers from AlGaN to indium‐containing alloys is also investigated; it highlights the transformation of step‐flow to three‐dimensional growth mode. It is also shown that at the coalescence boundaries of growth hillocks, defects are generated which act as electrically active electron traps.