We use Raman scattering to investigate the composition behavior of the E 2h and A 1 (LO) phonons of In x Ga 1Àx N and to evaluate the role of lateral compositional fluctuations and in-depth strain/ composition gradients on the frequency of the A 1 (LO) bands. For this purpose, we have performed visible and ultraviolet Raman measurements on a set of high-quality epilayers grown by molecular beam epitaxy with In contents over a wide composition range (0.25 < x < 0.75). While the as-measured A 1 (LO) frequency values strongly deviate from the linear dispersion predicted by the modified random-element isodisplacement (MREI) model, we show that the strain-corrected A 1 (LO) frequencies are qualitatively in good agreement with the expected linear dependence. In contrast, we find that the strain-corrected E 2h frequencies exhibit a bowing in relation to the linear behavior predicted by the MREI model. Such bowing should be taken into account to evaluate the composition or the strain state of InGaN material from the E 2h peak frequencies. We show that in-depth strain/composition gradients and selective resonance excitation effects have a strong impact on the frequency of the A 1 (LO) mode, making very difficult the use of this mode to evaluate the strain state or the composition of InGaN material. V C 2012 American Institute of Physics.

GaN thin films were grown by electron cyclotron resonance molecular beam epitaxy on Si(111) wafers. X-ray diffraction and transmission electron microscopy revealed that the thin films were single crystals with a hexagonal symmetry and a clear textured structure. The average column size was determined to be close to 100 nm in diameter. Despite the large defect density, a strong room temperature photoluminescence signal with a full width at half maximum of 138 meV was observed from these samples. The surface exhibited random array of sharp tips at the microscopic level with about 5×109 tips/cm2 density. The field emission characteristics of the as-grown thin films were measured, and a threshold electric field as low as 30–40 V/μm and an emission current density of more than 100 mA/cm2 were obtained.

Articles you may be interested inEffects of lateral overgrowth on residual strain and In incorporation in a-plane InGaN/GaN quantum wells on rsapphire substrates J. Appl. Phys. 113, 023506 (2013); 10.1063/1.4774302 Raman scattering by the E 2h and A 1(LO) phonons of In x Ga1x N epilayers (0.25 x J. Appl. Phys. 111, 063502 (2012); 10.1063/1.3693579 Raman and emission characteristics of a-plane InGaN/GaN blue-green light emitting diodes on r-sapphire substratesWe perform high-pressure Raman-scattering measurements on different In x Ga 1-x N/Si(111) epilayers (0.19 < x < 0.45). We find that the experimental pressure coefficient of the A 1 (LO) mode measured in these samples is larger than that expected from the linear interpolation between the corresponding values of GaN and InN. Similar measurements in InGaN epilayers grown on GaN/sapphire templates yield much lower values, below the linearly interpolated pressure coefficients. We conclude that the phonon pressure coefficients measured in InGaN are mainly determined by the different compressibility of the substrate and epilayer material. Neglecting substrate effects may yield highly inaccurate phonon pressure coefficients and mode Gr€ uneisen parameters. V C 2014 AIP Publishing LLC. [http://dx.

In-situ depositions and reactions are utilized in the study of phase formation from solid phase reactions. We report on the formation of epitaxial GaAs and the formation of NiAs or Ni2Ga3 by the exposure of Ni3GaAs to As4 or Ga fluxes. In-situ annealing of Ni on MBE-grown GaAs leads to Ni3GaAs, and subsequent reaction with As4 or Ga drives regrowth of GaAs. The structures were analyzed by RBS, XRD, TEM, and in-situ electrical measurements.

GaN thin films were deposited by reactive molecular beam epitaxy method with a modified ASTeX®  compact electron cyclotron resonance (ECR) plasma source of nitrogen. The effect of different ECR exit apertures on the growth rate and photoluminescence properties of GaN films was investigated. An aperture with a matrix of 1.6 mm holes allowed for GaN films with good optical properties at growth rates up to 1 μm/h. Apertures of larger diameter resulted in semi-insulating films. Room temperature photoluminescence for both undoped and Si-doped GaN films with full width at half maximum less than 100 meV has been obtained at the highest growth rates. We suggest that such an aperture effectively blocks the energetic ions from reaching the substrate thus reducing ion damage, resputtering, and increasing the Ga surface population. It also creates a higher pressure inside the ECR resonator, and therefore, provides a higher flux of active species. While further optimization will result in better GaN film quality, our results suggest that the growth rate in Ga-rich condition is limited by the microwave power available in the ASTeX compact ECR source.