A. Vasson

Determination of the refractive indices of AlN, GaN, and AlxGa1−xN grown on (111)Si substrates

The refractive indices of several AlxGa1−xN alloys deposited on silicon are determined by ellipsometry and reflectivity experiments at room temperature. The AlGaN layers are grown on (111)Si substrate by molecular-beam epitaxy on top of an AlN/GaN/AlN buffer in order to reduce the strain of the alloy. The Al composition is deduced from energy dispersive x-ray spectroscopy and photoluminescence experiments. The refractive index n and the extinction coefficient k are determined in the 300–600 nm range. For the transparent region of AlxGa1−xN, the refractive index is given in form of a Sellmeier law.

Strong light-matter coupling at room temperature in simple geometry GaN microcavities grown on silicon

The reflectance spectra of simple design GaN-based microcavities have been studied in the 5 K–300 K range. The epitaxial structure consists of the silicon substrate and the stack of buffer layers as the back mirror, a GaN active layer, and a 100 A thick aluminium layer as the top mirror. Active layer thicknesses of λ∕2, λ, or 3λ∕2 were investigated. The samples with GaN thicknesses λ∕2 and λ display an anticrossing behavior between the cavity and exciton modes, with measured Rabi splittings of 47 and 60 meV, respectively, both at 5 K and room temperature.

Temperature dependence of optical properties of h-GaN films studied by reflectivity and ellipsometry

Spectroscopic ellipsometry (SE) carried out at 300 K together with reflectivity measurements performed from 5 to 300 K are used to determine the temperature dependence of the refractive index of hexagonal GaN films between 360 and 600 nm. The refractive index is well described with a Sellmeier dispersion law and its variation with temperature is given. Below the band gap, the three excitonic features (labelled A, B and C) appearing in the reflectivity spectra are analysed within a multi-polariton model which includes the spatial dispersion. The transition energy, broadening parameter and oscillator strength are derived. The temperature dependence of A and B broadening parameters is analysed.

Experimental observation of strong light-matter coupling in ZnO microcavities: Influence of large excitonic absorption

We present experimental observation of the strong light-matter coupling regime in ZnO bulk microcavities grown on silicon. Angle resolved reflectivity measurements, corroborated by transfer-matrix simulations, show that Rabi splittings in the order of 70 meV are achieved even for low finesse cavities. The impact of the large excitonic absorption, which enables a ZnO bulk-like behavior to be observed even in the strong coupling regime, is illustrated both experimentally and theoretically by considering cavities with increasing thickness.

Growth by molecular beam epitaxy and optical properties of a Ten-period AlGan/AlN distributed Bragg reflector on (111)Si

This paper reports the growth of GaN, (Al,Ga)N and AlN layers on (111)Si substrates by molecular beam epitaxy using ammonia. Using proper conditions, GaN layers with threading dislocation densities as low as 5 x 10 9 cm -2 can be obtained on (111)Si. The structural and optical properties of GaN and (Al,Ga)N have been studied using electron microscopy, photoluminescence and reflectivity. In particular, the tensile strain has been assessed. Finally, a ten-period Al 0.2 Ga 0.8 N/AlN Bragg mirror has been grown, with a UV (340 nm) centered bandwidth of 35 nm and peak reflectivity of 78%.

Optical investigation in ultrathin InAs/InP quantum wells grown by hydride vapor‐phase epitaxy

Single and multiple InAs/InP strained quantum wells have been grown by hydride vapor‐phase epitaxy (HVPE). A compact set of vent/run valves monitored by manifold switches and a computer allowed the vapor species to be changed. InAs growth times of 4–24 s followed by etching times of 7–14 s, in an InCl, HCl, and H2 atmosphere, were used to control the thickness and interface abruptness. Low‐temperature photoluminescence (PL) spectra have revealed emissions either in the form of a single peak or well‐resolved multiple peaks attributed to monolayer variation in quantum‐well thickness. The thinnest well obtained, observed for the first time by HVPE, has a PL energy transition at 1.28 eV. Experimental data agree well with theoretical calculations, taking into account strain effects on band structure and effective masses. The full widths at half maximum indicate good interfacial abruptness.

First investigation on an ultra-thin InAs/InP single quantum well by thermally detected optical absorption spectroscopy

A non-conventional technique of thermally detected adsorption (TD-OA) is used to study a strained InAs/InP quantum well with thickness between two and tree monolayers. The spectrometer and TD cell are briefly described and the TD-OA spectra are presented. Three signals due to the InAs well are identified. The simple envelope-function approach is sufficient for the interpretation of these, which are attributed to transitions involving the heavy-hole levels. However, for the light-hole-related peak, a more sophisticated theory, taking into account the coupling between the light hole and spin-orbit split-off states, is necessary to fit the result.

Influence of the mirrors on the strong coupling regime in planar GaN microcavities

The optical properties of bulk

Modelling of thermally detected optical absorption and luminescence of (In,Ga)N/GaN heterostructures

lambda/2

IMPROVED GAINAS GAAS HETEROSTRUCTURES BY HIGH GROWTH-RATE MOLECULAR-BEAM EPITAXY

GaN microcavities working in the strong light-matter coupling regime are investigated using angle-dependent reflectivity and photoluminescence at 5 K and 300 K. The structures have an Al