J. Calas

The physics of heteroepitaxy of 3C–SiC on Si: role of Ge in the optimization of the 3C–SiC/Si heterointerface

Abstract We demonstrate that the S-correlated theory of misfit induced superstructures and its continuity criteria, defined within the framework of the elasticity theory, enables to predict the composition of buffer layers which can optimize the 3C–SiC/Si interface. The effect of incorporating Ge atoms to the carbon source is investigated and the results are compared with the experimental results.

MOCVD Growth of Cubic Gallium Nitride: Effect of V/III Ratio

We have grown cubic GaN on GaAs(001) substrates by MOCVD using a double step process with a buffer deposition at 400 °C. The purpose of the buffer deposited at very low temperature is to prevent GaAs decomposition at growth temperature. We have focused on the effect of the NH3/TEGa molar ratio on the growth of this metastable phase. We have assessed the crystalline quality using X-ray diffraction in the θ–2θ mode, and have used low temperature (2 K) PL for evaluating the optical properties of the GaN films. We found an optimum V/III ratio of 1250 at the growth temperature of 800 °C.

MOVPE of high quality ZnSe: Role of mismatch on reflectivity and photoconductivity

Abstract Metalorganic vapor phase epitaxy was used to grow high quality ZnSe. Two procedures were employed involving growth both at 300 and 500 °C. To achieve epitaxy of ZnSe at temperatures as low as 300 °C from alkyls, it was necessary to use a special double zone reactor. Reflectivity spectra show the lattice deformation due to mismatch for layers thinner than 1 μm. Photoconductivity responses related to the layer thickness are also reported.

Contamination effects from tellurium in ZnS-ZnSe superlattices

Abstract We have studied the temperature dependence of the photoluminiscence of tellurium-doped ZnS-ZnSe superlattices. By comparing the reflectivity and photoluminescence data, we were able to identify both free exciton recombination and self-trapped exciton band energy split by 90 meV. The behaviour of the photoluminescence with temperature results from trapping versus detrapping effects which are ruled by an activation energy of 80 meV. This behaviour is analysed in the context of a configuration coordinate diagram.

Excitonic properties and magnetooptical characterization of (Zn, Cd)SeZnSe heterostructures

Abstract We present an experimental and theoretical study of optical and magneto-optical properties of excitons in strained layer ZnCdSeZnSe superlattices. The optical characterizations of these structures are based on photoluminescence and reflectivity measurements at 2 K. The excitonic transition energies are determined experimentally and are found in agreement with the predictions of the envelope function, taking into account band offsets and exciton binding energies. These binding energies and also the oscillator strengths are calculated using a recent formalism of fractional dimensional space (αD) and compare favourably with variational calculations. Magnetoreflectivity measurements are performed up to 5.5 T. They permit us to calculate the Zeeman splitting of | ± 3 2 , ± 1 2 〉 and | ± 1 2 , ± 1 2 〉 transitions and then, to deduce the corresponding effective g- values g 1 2 and g 1 2 . In our knowledge, our results concerning the calculations of ΔE 1 2 and then g 1 2 for such superlattices are the first ones and permit us to confirm the interlevel mixing in these structures.

Optical and magneto-optical differential spectroscopy of a ZnCdSe-ZnSe superlattice

Abstract We report on optical and magneto-optical studies of a ZnCdSe-ZnSe strained layer superlattice. This structure was grown by metal-organic vapour phase epitaxy (MOVPE) and consisted of 40 periods of 72 A ZnCdSe layer and 49 A ZnSe layer with cadmium composition equal to 4%. Photoluminescence, reflectivity and magnetocircular dichroism experiments at 2 K were used to identify e 1 -hh 1 and e 1 -lh 1 excitonic transitions. By comparing these experimental transitions with the calculated ones, we have determined the valence and the conduction band offsets. In these calculations, we have included values of the binding energies related to the different transitions. These binding energies are calculated within the formalism of fractional dimensional space. Zeeman splitting of ¦ ± 3/2, ± 1/2〉 and ¦ ± 1/2, ∓1/2〉 transitions are calculated at 5.5 T and the corresponding effective g -values g 3/2 and g 1/2 are deduced.

Optical properties of Zn1−xCdxSe-ZnSe superlattices grown by metal organic vapour phase epitaxy

An investigation of the reflectivity and photoluminescence spectra of 40-period Zn1−xCdxSe-ZnSe strained layer superlattices is reported. Superlattices with cadmium composition between 3% and 10% were grown by metal organic vapour phase epitaxy. The well and barrier widths were varied in order to study the tunnelling effect in the superlattices. This effect was shown to be large not only for the excited states (e2hh2 transitions for the 10% cadmium composition) but also for e1hh1 transitions despite the large heavy hole effective mass. The band discontinuities were determined by calculating the transition energies within the envelope function framework generalized to strained layers. It was found that for all superlattices the mechanical state is pseudomorphic and that the heavy hole band offset is 32% of the energy difference of the strained band gaps. The binding energies and the oscillator strengths of the various excitonic transitions were calculated within the formalism of fractional-dimensional space and compared with variational calculations reported in the literature.

A Study of the Photoluminescence and Reflectivity Spectra of MOCVD Grown MnSe

Photoluminescence (PL) experiments at 2K are performed on MOCVD grown MnSe. The precursors used in the growth stage are methylpentacarbonylmanganese and diethylselenide. Pyrolysis of the percursors is realized inside a gradient reactor under a constant H 2 flux, between 280-55°TC. The compound is epitaxially grown on various substrates (Si, InP, GaSb, GaAs, ZnTe/GaAs, etc.). On some of these samples the compound presents a zinc blende structure, while in the other samples rock salt formation has been identified. The first substrate is used because of its interest in Si technology, while the others are used because MnSe can be grown in the zinc blende phase for very thin layers. For the first time x-ray diffraction data has allowed us to determine the lattice constant of zincblende MnSe (a Mnse (oct) =5.818A), confirming the close approximation (a ∼ 5.9A) used from the Zn 1-x Mn x Se alloy. These compounds have visible Mn ++ transitions at 2.12-5eV; other features are also visible at 2.3-4, 2.7, and 3.0eV. The energy gap transition of tetrahedral thin film layers of MnSe is seen for the first time in PL spectra. A temperature dependant PL study is performed on MnSe in the 2-200K range. Reflectivity experiments are used to attempt to identify the internal manganese transitions. A qualitative PL analysis of the samples grown at different temperatures and on different substrates is provided. A Stokes shift is encountered when the results are compared.