GaN InN Research Articles

Rare earth ion implantation and optical activation in nitride semiconductors for multicolor emission

In order to understand the behavior of nitride semiconductors when submitted to ion implantation, we have used 300 keV europium at fluences from 1012 to above 1017 ions cm−2. Subsequently, Rutherford backscattering (RBS), x-ray diffraction (XRD), and transmission electron microscopy (TEM) were used to investigate the evolution of damage. The optical properties were investigated prior to and after annealing. It was found that the behavior of the three compounds (AlN, GaN InN) under ion implantation is rather different: whereas InN breaks down at very low fluences (∼1012 ions cm−2), the damage formation mechanisms are similar in AlN and GaN. In both compounds, extended defects such as stacking faults play a critical role. However, they exhibit different stability, as a consequence, GaN transforms to nanocrystalline state from the surface at a fluence of around 2.5 × 1015 ions cm−2, whereas AlN undergoes a chemical amorphization starting at the projected range (Rp), when implanted to extremely high Eu fluences >1017 ionscm−2. As for the optical activation, the formation of highly stable extended defects in these compounds constitutes a real challenge for the annealing of heavily doped layers, and it was noticed that for a substantial optical activation, the implantation fluences should be kept low (<1015 Eu at cm−2).

Vibrational properties of (0 0 1) III–V nitride superlattices

We study the acoustic waves of superlattices grown along the [0 0 1] direction and formed by slabs of cubic III–V nitride. We consider structures formed by combining AlN, GaN and InN in the zinc-blende structure because of the possible applications of these materials. The anisotropy of the materials has been taken into account and the different propagation directions including symmetry directions and general directions have been considered. The dispersion relations for these propagation directions have been obtained. The evolution of gaps along the propagation directions is studied. Total gaps for some propagation directions and frequency ranges are found in GaN–InN superlattices.

First principles phase diagram calculations for the wurtzite-structure systems AlN–GaN, GaN–InN, and AlN–InN

First principles phase diagram calculations were performed for the wurtzite-structure quasibinary systems AlN–GaN, GaN–InN, and AlN–InN. Cluster expansion Hamiltonians that excluded, and included, excess vibrational contributions to the free energy, Fvib, were evaluated. Miscibility gaps are predicted for all three quasibinaries, with consolute points, (XC,TC), for AlN–GaN, GaN–InN, and AlN–InN equal to (0.50, 305K), (0.50, 1850K), and (0.50, 2830K) without Fvib, and (0.40, 247K), (0.50, 1620K), and (0.50, 2600K) with Fvib, respectively. In spite of the very different ionic radii of Al, Ga, and In, the GaN–InN and AlN–GaN diagrams are predicted to be approximately symmetric.

Phase Separation in InGaN Epitaxial Layers

Epitaxial layers of InGaN were deposited by metalorganic chemical vapor deposition on a GaN layer/sapphire substrate in order to ascertain compositional variation in the GaN–InN system. Samples were examined with In contents from x = 0.09 to 0.31. Plan-view images obtained by transmission electron microscopy reveal a domain structure within which the composition is modulated. Satellites appear around the fundamental reflections in the diffraction pattern. The spacing between the satellite and the reflection can be related to the wavelength of the modulations. Equations are derived for modulations in the [100] and [110] directions. Modulations were measured in the [100] direction and found to be about λ = 3.2 nm for all samples. Strain energy considerations explain the observation of modulations along different directions.

Periodic composition modulations in InGaN epitaxial layers

InGaN epitaxial layers grown by metalorganic chemical vapor deposition were investigated in order to understand the occurrence of composition modulations in the GaN–InN system. The In contents of the samples were determined to be x=0.21 and 0.31. Transmission electron microscopy was performed on [0001], [101̄0], and [112̄0] zone-axis specimens. Plan-view images display a domain structure, representing regions in which the directions of the modulations differ. Intersections between domains occur in 〈101̄0〉, and 〈112̄0〉, and other directions. Satellite spots appear in selected-area diffraction patterns. These observations can be explained by diffraction effects resulting from periodic composition modulations. An equation was derived relating the spacing between the satellites and the reflections to the wavelength of the modulations in the wurtzite structure. The sample with x=0.21 had a wavelength of λ=3.1±1.3 nm and the one with x=0.31 had λ=3.2±1.3 nm. Since Young’s modulus is isotropic in the (0001) plane, no particular direction is favored for the modulations based on strain energy considerations. This result is consistent with the observation of the variously oriented domains and satellites.

Phase separation in InGaN thick films and formation of InGaN/GaN double heterostructures in the entire alloy composition

We report the growth of InGaN thick films and InGaN/GaN double heterostructures by molecular beam epitaxy at the substrate temperatures 700–800 °C, which is optimal for the growth of GaN. X-ray diffraction and optical absorption studies show phase separation of InN for InxGal−xN thick films with x&amp;gt;0.3. On the other hand, InxGal−xN/GaN double heterostructures show no evidence of phase separation within the detection capabilities of our methods. These observations were accounted for using Stringfellow’s model on phase separation, which gives a critical temperature for miscibility of the GaN–InN system equal to 2457 K.

Fundamental absorption edge in GaN, InN and their alloys

Optical measurements were performed near the fundamental absorption edge for thin polycrystalline films with the entire region of composition in the GaNInN quasi-binary system. The direct energy gap E g for GaN and InN was found to be 3.40 and 1.95 eV, respectively. The dependence of E g on composition was found to deviate downward from linearity. The degree of bowing was expressed well by the theoretical bowing parameter (1.05 eV) calculated by the dielectric method.