BOUGRIOUA , Z.

The microstructure of (11‐20) GaN films grown on (1‐102) sapphire substrates is studied by transmission electron microscopy. The predominant defects emerging at the surface of a 1‐2 μm thick layers are basal stacking faults of I1 type (1/6<20‐23> displacement vector). These defects are either terminated in the films by partial dislocations with...

AlGaN/GaN high-electron mobility transistors (HEMTs) structures regrown by metalorganic vapour phase epitaxy (MOVPE) on semi-insulating (SI) GaN templates, after exposure to air, results in the presence of parasitic conducting channels at regrowth interface. Air contamination of the SI GaN templates generates this parallel conduction. The...

Strategies for maintaining a low threading dislocation density in highly resistive GaN layers grown by MOVPE on sapphire or SiC substrates using Fe modulation doping are presented. Sheet resistances as high as 1E+8 Ω□ for dislocation densities lower than 8E+8 /cm² have been obtained. 2DEGs created at the AlGaN/GaN:Fe interface have good...

In order to get semi‐insulating GaN layers with a low dislocation density on sapphire, two kinds of Fe doping were explored by low pressure metalorganic vapour phase epitaxy (LP‐MOVPE): the modulation doping (MD) and the continuous doping (CD). The high crystalline quality and the semi‐insulating character are obtained in the case of the Fe‐MD...

The relaxation mechanisms in metal-organic vapor phase epitaxy grown (Al,Ga)N∕GaN heterostructures are studied. The first stage of the relaxation process is a two-dimensional–three-dimensional growth transition with the formation of mesalike islands separated by V-shaped trenches. The tensile stress relief is obtained by an elastic relaxation...

The microstructure of nonpolar heteroepitaxial wurtzite films (GaN and ZnO-based) is dominated by the presence of planar basal stacking faults (BSFs). In this paper, transmission electron microscopy studies of both GaN and ZnO nonpolar films oriented either (11–20) or (1–100) and grown on sapphire substrates, permit to propose and evaluate...

GaN has been grown using Si/N treatment growth by MOVPE on sapphire (0001) in a home-made vertical reactor. The growth was monitored by in situ laser reflectometry. The morphological, electrical and optical properties of GaN are investigated at all the growth stages. To this aim, the growth was interrupted at different stages. The obtained...

Nonpolar (11-20) (Ga,In)N multi-quantum wells have been studied by polarized, temperature dependent photoluminescence (PL). A non monotonic temperature dependence of the difference in PL peak energies recorded for E parallel to c or E perpendicular to c, and of the polarization ratio is observed. We interpret these effects by first an...

The in-plane polarities of GaN and ZnO non-polar films deposited on r - and m-sapphire are compared. The polarity is unique on r-sapphire and mixed on m-sapphire because the direction on the substrate surface parallel to the wurztite c-direction is polar in the first case and nonpolar in the second case. Furthermore, on r-sapphire where GaN and...

Strain relaxation mechanisms in metal-organic vapour phase epitaxy grown (Al,Ga)N/GaN heterostructures are presented. Relaxation first occurs through a 2D–3D transition. For pure AlN, misfit a-type dislocations are introduced at the coalescence front of growth islands. For (Al,Ga)N (Al concentration≤70%), the second relaxation step is cracking....

The characteristics of surface acoustic waves (SAWs) in GaN layers grown on c-plane sapphire are investigated. Besides Rayleigh mode, Sezawa and Love modes, which are confined in the nitride layers, arise because of the slow sound propagation in GaN compared with the substrate. In addition, pseudo-SAWs leaking into the bulk are observed. The...

The transport and quantum lifetimes were respectively deduced from low-temperature mobility and Shubnikov-de Haas measurements as a function of carrier density in metal organic vapor phase epitaxy-grown AlGaN/GaN/sapphire heterostructures. We show experimentally that the lifetime ratio varies as a bell curve, qualitatively confirming a recent...

Highly resistive GaN (>1E+8 Ω#) is grown by MOVPE on sapphire with dislocation density in the range 1E+8 to 8E+8 /cm², using Fe modulation doping. High mobility 2DEGs are created at AlGaN/GaN:Fe interface for moderate Al composition: 2200 cm²/V/s at n_s∼7.6E+12 /cm². Good DC and RF small signal behaviour could be obtained in HEMTs processed on...

New conditions for one‐step ELO were implemented to grow coalesced (11equation image0) non‐polar and (11equation image2) semi‐polar GaN layers starting, respectively, from R ‐ and M ‐plane sapphire. A great part of the stacking faults (SFs) and dislocations are filtrated resulting in GaN material with better structural and optical properties....

The effect of Fe and Si doping in GaN grown epitaxially on Al2O3 is studied using Extended X-ray Absorption Fine Structure (EXAFS) and Raman spectroscopies. The EXAFS analysis shows that in GaN samples grown by Molecular Beam Epitaxy (MBE) at 750 °C the Ga–Ga distance is about 0.19% longer than the corresponding distance in samples grown by...

Al, Au, Ti/Al and Ti/Au contacts were prepared on n-GaN and annealed up to 900 °C. The structure, phase and morphology were studied by cross-sectional transmission and scanning electron microscopy as well as by X-ray diffraction (XRD), the electrical behaviour by current–voltage measurements. It was obtained that annealing resulted in...

High electron mobility field effect transistors were fabricated on AlGaN/GaN heterostructures and their magnetoresistance was measured at 4.2 K up to 10 T with simultaneous modulation of the gate potential. Low and high magnetic field data were used to determine the electron mobility (mu) and concentration (n), respectively, in the gated part...

The anisotropic propagation of surface acoustic modes in GaN and AlN induced by the -sapphire substrate is presented. In the GaN case, the slow acoustic propagation velocity of GaN compared with sapphire leads to guided modes in the overlayer, which propagate at higher velocities but are more attenuated than the Rayleigh mode. Above the...

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In this work, AlGaN/GaN high electron mobility transistors have been grown by ammonia source molecular beam epitaxy (MBE) on silicon (1 1 1), silicon carbide and GaN templates on sapphire. The structural and electrical properties of these layers have been studied in order to determine the impact of substrate choice and buffer layer on active...