José M. Mánuel

Evaluation of interpolations of InN, AlN and GaN lattice and elastic constants for their ternary and quaternary alloys

Structural and compositional data were collected for several high-quality strained InGaN, InAlN, AlGaN and InAlGaN layers with various compositions. Based on these results, the InN/AlN/GaN molar fractions of every film were indirectly estimated by the application of Vegards law (Vegard 1921 Z. Phys. 5 17) to lattice and elastic constants of the binaries and by an alternative approach proposed by (Williams et al 1978 J. Electron. Mater. 7 639) (even considering possible mistakes in its application). True compositions were independently assessed by x-ray spectroscopy or Rutherford backscattering spectrometry. The results of both interpolation models are highlighted in utilizable contour and surface ternary plots of lattice constants and biaxial strain relaxation coefficients calculated for the whole compositional range. Calculated compositions from Vegards law best fit the measured values. Finally, it is geometrically demonstrated that there are wrong assumptions in the Williams et al model, so that Vegards law should only be used to successfully determine the compositions of ternary and quaternary III-N nitrides.

Structural and optical characterization of Mg-doped GaAs nanowires grown on GaAs and Si substrates

We report an investigation on the morphological, structural, and optical properties of large size wurtzite GaAs nanowires, low doped with Mg, grown on GaAs(111)B and Si(111) substrates. A higher density of vertical nanowires was observed when grown upon GaAs(111)B. Very thin zinc-blende segments are observed along the axis of the nanowires with a slightly higher linear density being found on the nanowires grown on Si(111). Low temperature cathodoluminescence and photoluminescence measurements reveal an emission in the range 1.40–1.52 eV related with the spatial localization of the charge carriers at the interfaces of the two crystalline phases. Mg related emission is evidenced by cathodoluminescence performed on the GaAs epilayer. However, no direct evidence for a Mg related emission is found for the nanowires. The excitation power dependency on both peak energy and intensity of the photoluminescence gives a clear evidence for the type II nature of the radiative transitions. From the temperature dependence on the photoluminescence intensity, non-radiative de-excitation channels with different activation energies were found. The fact that the estimated energies for the escape of the electron are higher in the nanowires grown on Si(111) suggests the presence of wider zinc-blende segments.

Near-infrared emitting In-rich InGaN layers grown directly on Si: Towards the whole composition range

The authors report compact and chemically homogeneous In-rich InGaN layers directly grown on Si (111) by plasma-assisted molecular beam epitaxy. High structural and optical quality is evidenced by transmission electron microscopy, near-field scanning optical microscopy, and X-ray diffraction. Photoluminescence emission in the near-infrared is observed up to room temperature covering the important 1.3 and 1.55 μm telecom wavelength bands. The n-InGaN/p-Si interface is ohmic due to the absence of any insulating buffer layers. This qualitatively extends the application fields of III-nitrides and allows their integration with established Si technology.

N-type conductivity and properties of carbon-doped InN(0001) films grown by molecular beam epitaxy

In this work, we have analyzed the effect of intentional carbon doping on molecular beam epitaxy grown In-polar InN epilayers using carbon bromide (CBr4) as dopant source. Hall effect measurements, high resolution X-ray diffraction, atomic force microscopy, transmission electron microscopy, secondary ion mass spectrometry, spectroscopic ellipsometry, as well as X-ray photoelectron spectroscopy were employed to characterize the influence of different dopant concentrations on the electrical, optical, crystallographic, morphological, and electronic properties of InN. It was found that the electron concentration increases linearly with the incorporation of carbon pointing towards the effect of n-type doping and that incorporated C impurities reduce the electron mobility within the InN films. This correlation is further reflected in associated properties such as the onset of optical absorption, the plasmon frequency, the effective electron mass and the position of the bulk and surface Fermi level. Furthermore,...

Spontaneous formation of InGaN nanowall network directly on Si

We present the study on epitaxial growth of an InGaN nanowall network directly on Si by plasma-assisted molecular beam epitaxy. Scanning electron microscopy, high-resolution X-ray diffraction, and transmission electron microscopy together with energy-dispersive X-ray analysis infer the crystalline nature of the InGaN nanowall network, oriented along the C-axis, with In composition ranging from pure GaN to 40%. Room temperature photoluminescence is observed, indicating good optical quality. The nanowall network is highly in-plane electrically conductive.

Stranski-Krastanov InN/InGaN quantum dots grown directly on Si(111)

The authors discuss and demonstrate the growth of InN surface quantum dots on a high-In-content In0.73Ga0.27N layer, directly on a Si(111) substrate by plasma-assisted molecular beam epitaxy. Atomic force microscopy and transmission electron microscopy reveal uniformly distributed quantum dots with diameters of 10–40 nm, heights of 2–4 nm, and a relatively low density of ∼7 × 109 cm−2. A thin InN wetting layer below the quantum dots proves the Stranski-Krastanov growth mode. Near-field scanning optical microscopy shows distinct and spatially well localized near-infrared emission from single surface quantum dots. This holds promise for future telecommunication and sensing devices.

Uniform Low-to-High In Composition InGaN Layers Grown on Si

Uniform, compact, and thick InGaN layers are grown on Si(111) substrates by plasma-assisted molecular beam epitaxy without any buffer layers at low temperatures of around 320 °C. By adjusting the Ga/In flux ratio, InGaN layers with In compositions between 10 and 33% are obtained, providing emission covering the whole visible spectral range. The In composition varies less than 2% over large areas, and the single-crystalline hexagonal InGaN layers have a well-defined epitaxial relationship with the Si substrate. Photoluminescence is observed up to room temperature, opening the prospect for the direct integration of InGaN light-emitting devices with Si technology.

Inline electron holography and VEELS for the measurement of strain in ternary and quaternary (In,Al,Ga)N alloyed thin films and its effect on bandgap energy

We present the use of (1) dark‐field inline electron holography for measuring the structural strain, and indirectly obtaining the composition, in a wurtzite, 4‐nm‐thick InAlGaN epilayer on a AlN/GaN/AlN/GaN multinano‐layer heterosystem, and (2) valence electron energy‐loss spectroscopy to study the bandgap value of five different, also hexagonal, 20–50‐nm‐thick InAlGaN layers. The measured strain values were almost identical to the ones obtained by other techniques for similarly grown materials. We found that the biaxial strain in the III‐N alloys lowers the bandgap energy as compared to the value calculated with different known expressions and bowing parameters for unstrained layers. By contrast, calculated and experimental values agreed in the case of lattice‐matched (almost unstrained) heterostructures.

Engineering of III-Nitride Semiconductors on Low Temperature Co-fired Ceramics

This work presents results in the field of advanced substrate solutions in order to achieve high crystalline quality group-III nitrides based heterostructures for high frequency and power devices or for sensor applications. With that objective, Low Temperature Co-fired Ceramics has been used, as a non-crystalline substrate. Structures like these have never been developed before, and for economic reasons will represent a groundbreaking material in these fields of Electronic. In this sense, the report presents the characterization through various techniques of three series of specimens where GaN was deposited on this ceramic composite, using different buffer layers, and a singular metal-organic chemical vapor deposition related technique for low temperature deposition. Other single crystalline ceramic-based templates were also utilized as substrate materials, for comparison purposes.

High-Resolution Electron Microscopy of Semiconductor Heterostructures and Nanostructures

This chapter briefly describes the fundamentals of high-resolution electron microscopy techniques. In particular, the Peak Pairs approach for strain mapping with atomic column resolution, and a quantitative procedure to extract atomic column compositional information from Z-contrast high-resolution images are presented. It also reviews the structural, compositional, and strain results obtained by conventional and advanced transmission electron microscopy methods on a number of III–V semiconductor nanostructures and heterostructures.