G. Orsal

Distributed Bragg reflectors based on diluted boron-based BAlN alloys for deep ultraviolet optoelectronic applications

Highly reflective deep UV distributed Bragg reflectors (DBRs) based on the BAlN material system have been grown by metalorganic vapour phase epitaxy on AlN template substrates. These structures make use of the transparency of BAlN in the deep UV and the high refractive index contrast between BAlN and AlN, which has been demonstrated to exceed 0.27 at 280 nm. 18-pair BAlN/AlN DBRs showed experimental peak reflectivity of 82% at 311 nm and a stop-bandwidth of 20 nm. At 282 nm, a 24-pair BAlN/AlN DBR structure is demonstrated with experimental peak reflectivity of 60% and stop-bandwidth of 16 nm.

Link between crystal quality and electrical properties of metalorganic vapour phase epitaxy InxGa1−xN thin films

We report on the crystal quality of metalorganic vapour phase epitaxy-grown InGaN with indium content ranging from 0% to 20%. Absorbance measurements are fit to a model including band tails and a defect represented as a Brendel oscillator (R. Brendel, Appl. Phys. A 50, 587, 1990). Band tail absorbance, corresponding to contorted bonds, increases with increased In content. Above 10% of In, the presence of another defect, the concentration of which increases with In content, has been correlated with x-ray diffraction and Raman. We suggest that this defect corresponds to nitrogen vacancies, in agreement with a reported model for GaN.

Epitaxial MOVPE growth of highly c-axis oriented InGaN/GaN films on ZnO-buffered Si (111) substrates

InGaN/GaN layers were grown on ZnO-buffered Si (111) substrates by metalorganic vapour phase epitaxy (MOVPE). The dissociation of ZnO observed during conventional MOVPE growth of InGaN/GaN was combated through the use of a low pressure/temperature MOVPE approach with N2 as a carrier gas and dimethylhydrazine added to the ammonia (nitrogen precursor) in order to enhance the concentration of atomic nitrogen at relatively low temperature. Electron Microscopy of cross-sections, High Resolution X-Ray Diffraction (HR-XRD), secondary ion mass spectroscopy and cathodoluminescence studies suggested that single phase wurtzite InGaN layers with between about 17.5 and 21.5% indium were grown epitaxially, with no evidence of back-etching of the ZnO templates. HR-XRD revealed highly pronounced c-axis texture for both the InGaN/GaN and ZnO. Immersion in dilute nitric acid dissolved the ZnO such that the InGaN/GaN could be lifted-off from the substrate.

Application of dilute boron B(Al,In,Ga)N alloys for UV light sources

In the last decades, development of the (Al,Ga,In)N materials has led to new generations of opto- and micro-electronic devices. More recently, novel B(Al,Ga,In)N alloys have been proposed for optical applications in the UV range. Since material containing boron possesses unique properties, the B(Al,Ga,In)N materials system is expected to permit the design of improved and/or novel devices. To evaluate this potential, an improved knowledge of the physical properties of these new materials will be required, however. In this work, investigation of optical, structural, and compositional properties of low-boron content BGaN and BAlN ternary and BInGaN quaternary materials grown through Metalorganic Vapor Phase Epitaxy (MOVPE) are presented. It is shown that inclusion of a small amount of boron strongly affects the optical properties allowing the fabrication of BGaN-based Distributed Bragg Reflectors (DBRs) or Distributed Bragg Confinement layers (DBCs) with large refractive index contrast. Indeed, 1% of boron in BGaN/GaN multilayer structures gives a refractive index contrast of more than 0.1, which is equivalent to that of AlGaN/GaN containing 22% aluminum. The potential of boron-based material technology is illustrated for visible range solar cells applications through the example of BInGaN with good crystalline quality grown on ZnO buffered silicon substrates. It was found that through boron introduction, reduced lattice mismatch, and thus reduced tensile strain, could be obtained for high In contents.