We present magnetotransport measurements on a high electron density AlGaN/GaN heterostructure with two subbands populated at T = 1.6 K. The transport scattering times, τtr, of each subband are first derived at low magnetic field by taking into account the magneto-intersubband scattering term. Then the quantum scattering times, τq, are extracted from independent Dingle plots, obtained at higher magnetic fields. All scattering times are studied as a function of the total electronic density, increased by the persistent photo-conductivity effect. A standard modelization, based on all common scattering mechanisms, reveals that the transport scattering time is governed by the short-range AlGaN/GaN interface roughness (IR) scattering, whereas the quantum scattering time is due to the smooth potential induced by remote ionized impurities (II) at the GaN surface. This intermediate situation of mixed disorder, where the τtr/τq ratio is greater than one, does not indicate that the mobility is limited by Coulomb scattering. It is due to the unusual condition, τtrII≫τtrIR≫τqII$ {\tau }_{\mathrm{t}r}^{\mathrm{II}}\gg {\tau }_{\mathrm{t}r}^{\mathrm{IR}}\gg {\tau }_{\mathrm{q}}^{\mathrm{II}}$.

AlxGa1- xN/GaN high electron mobility transistor (HEMT) structures grown by ammonia-source molecular beam epitaxy (MBE) are focused-ion-beam implanted with 300 keV Gd-ions at room temperature. The two-dimensional electron gas (2DEG) of these HEMT structures is located 27 nm underneath the sample surface. At 4.2 K, current-voltage characteristics across implanted rectangles show that the structures remain conducting up to a Gd-dose of 1×1012 cm-2. Anomalous Hall effect (AHE) is observed at T = 4.2 K for structures implanted with Gd, whose dose is 3×1011 cm-2. Measurements of AHE in the wide temperature range from 2.4 K to 300 K show that the magnetic ordering temperature of these structures is around 100 K. Therefore, these Gd-implanted HEMT structures containing the still conducting 2DEG, which is now embedded in a ferromagnetic semiconductor, open the possibility to polarize the electron spins.

We present an experimental study of asymmetric wafer deformation for 3C-SiC layers grown on deliberately misorientated silicon substrates. An asymmetric curvature has been observed both on (100) and (111) oriented layers. In this work we focus on the (100) oriented samples. The curvature of the wafers is studied as a function of wafer thickness and offcut angle. We look for the correlations between the observed asymmetric strain relaxation and the layer morphology and microstructure. We claim that different defect pattern, measured along [110] and [1-10] direction can be at the origin of almost complete relaxation of mismatch strain along the offcut direction.

During the last ten years, we have developed an efficient growth process of nitrides on silicon substrates by molecular beam epitaxy. In collaboration with partners AlGaN/GaN HEMTs on Si having promising performances have been fabricated. Focusing on the growth aspect and underlying some of the key issues, we present in this paper an overview of our contribution in the field of AlGaN/GaN HEMTs on Si substrates.

In this work, we study cubic SiC/Si (111) templates as an alternative for growing GaN on silicon. We first developed the epitaxial growth of 3C-SiC films on 50mm Si(111) substrates using chemical vapor deposition. Then, AlGaN/GaN high electron mobility transistors were grown by molecular beam epitaxy on these templates. Both the structural quality and the behavior of transistors realized on these structures show the feasibility of this approach.

A series of isothermal annealing experiments have been performed in the range 790–920°C under N2 flow in order to study the deuterium out-diffusion kinetics of Mg-doped GaN grown on sapphire under deuterated ammonia. The deuterium concentration was measured by SIMS analysis before and after each annealing step. The kinetics closely follow a first-order law. The activation energy related to the deuterium out-diffusion process is 3.1 eV. In addition, deuterium effusion measurements were performed measuring the molecular HD flux while the specimens were annealed in ultra high vacuum with a linear heating rate. In contrast to SIMS, this method detects the species that migrated out of the sample. Effusion peaks of the HD flux at 360 and 490°C are attributed to the fragmentation of adsorbed CHxDy complexes. The molecular HD flux starts increasing at 800°C which is the onset of the GaN decomposition and has its maximum at 920°C. This HD flux is accompanied by the desorption of H and D containing radicals and molecules desorbing above 900°C.

We have studied the influence of a deuterium diffusion on the electrical characteristics of the 2D gas present in AlGaN/GaN heterostructures. The deuterium diffusion is performed by exposing the structures to a rf remote deuterium plasma. We find that both the sheet carrier concentration and the electron mobility decrease and that these effects are partly reversible under thermal annealing. These results suggest that deuterium behave as acceptors in the 2D gas region. The negatively charged deuterium act as additional scattering centers for electrons.