E. Gil-Lafon

Characterization of GaAs conformal layers grown by hydride vapour phase epitaxy on Si substrates by microphotoluminescence cathodoluminescence and microRaman

Conformal growth of GaAs on Si consists of the confined lateral selective epitaxy of GaAs from GaAs oriented seeds on silicon, the vertical growth being stopped by an overhanging dielectric mask. Low defect GaAs films are obtained due to the absence of direct nucleation of the conformal GaAs epilayers on Si, and to the geometrical hindrance of the propagation of dislocations into the growing layer by the capping surface and by the substrate. GaAs conformal layers grown by hydride vapour phase epitaxy (HVPE) were characterised by microphotoluminescence (MPL), cathodoluminescence (CL) and microRaman. The GaAs conformal layers were found of superior quality since their luminescence emission was enhanced by several orders of magnitude with respect to the seeds directly grown on the Si substrate. CL and MPL images revealed in plane modulation of the luminescence emission. This modulation was associated with residual stress. MicroRaman measurements revealed stress distribution and eventually local symmetry breakdown.

Thermodynamical and kinetic study of the GaN growth by HVPE under nitrogen

Abstract The growth of GaN by HVPE was analysed by means of a thermodynamical and kinetic study. The thermodynamical constants of the reactions involved in the GaN growth and the partition functions of the molecules used in the kinetic study were calculated. The kinetic coefficients and the activation energies of the reactions were tabulated. Good agreement was obtained between the model and the experimental results. The influence of the reactor geometry and of the parasitic nucleation on the glass walls of the reactor was demonstrated. After analysing the physical phenomena which might take place in the vapour phase, we concluded that the vapour phase was not homogeneous. The reaction of formation of GaCl 3 from HCl and GaCl appears to be incomplete at the GaCl inlet, and almost complete over the substrate. Both effects explain the difficulty of growing GaN layers without extraneous deposit.

Two-particle surface diffusion-reaction models of vapour-phase epitaxial growth on vicinal surfaces

A generalization of the model of Burton, Cabrera and Frank of step flow epitaxial growth on vicinal surfaces in multi-component systems is presented. In particular, the present model addresses chemical vapour epitaxial growth, where the atomic or molecular species composing the crystal, or growth units, are carried to the substrate inside more complex molecules, or precursors, as well as molecular beam epitaxial growth of compound semiconductors. Surface diffusion, chemical reactions, and incorporation at steps are included in the model, that allows for an analytic computation of the growth rate. Special attention is paid to the delicate problem of boundary conditions at steps in a two-component system.

Direct condensation modelling for a two-particle growth system: application to GaAs grown by hydride vapour phase epitaxy

Abstract A new phenomenological model for the growth of GaAs in the GaCl/AsH 3 /HCl/H 2 vapour phase system is developed. The surface growth kinetics are modelled by taking into account the mechanisms of As and GaCl adsorption and chlorine desorption by H 2 into HCl. Two ad-species AsGaCl and AsGa interact on the surface through a reversible reaction, which is described through a modified two-particle Burton, Cabrera and Frank model. Kinetics data are determined by synthesising experimental and computed results. It is shown that when surface diffusion limitations can be neglected, the growth rate is reduced to a one-particle-like direct condensation expression, weighted by a sticking coefficient which takes into account the desorption frequency of the precursor AsGaCl and its reversible transformation into the crystal particle AsGa. Variations of the growth rate are discussed as a function of the ad-species surface coverage ratios and of the supersaturation of the vapour phase.

Temperature dependence of the Raman shift in GaAs conformal layers grown by hydride vapor phase epitaxy

Raman spectra between room temperature and 350 °C were measured in GaAs layers grown by hydride vapor phase epitaxy on Si substrates using the selective conformal growth method. The contributions of the thermal expansion, anharmonic phonon decay, and strain are considered in order to analyze the Raman data. The tensile strain in the conventional GaAs/Si seed and in the conformal GaAs layers was determined from the Raman spectra. It is shown that the thin SiO2 layer between the GaAs and the Si substrate is a compliant layer that plays an important role in the reduction of the dislocation density in the conformal layers. The tensile strain in conformal layers was higher than in the conventional GaAs/Si layers, in which strain is relieved by the high density of dislocations.

Stress distribution mapping of GaAs on Si conformal layers

Cathodoluminescence and micro-Raman studies of GaAs on Si layers grown by the conformal method show a characteristic quasiperiodic modulation of the stress distribution perpendicular to the growth direction. Using the capability of the spectral imaging in the cathodoluminescence technique, the stress distribution has been directly mapped. The Raman data give accurate information of the stress level variations in the upper part of the samples, which compare well with the luminescence data. The origin of the quasiperiodic stress variations are discussed in terms of the growth geometry, taking account of the presence of a compliant thin SiO2 layer in between the Si substrate and the ⟨110⟩ growing GaAs layer.

Kinetic expression and study of the growth rate of mismatched (Ga,In)AsInP structures grown by hydride vapour phase epitaxy

Abstract A theoretical analysis of the growth rate of mismatched Ga x In 1− x As alloys ( x = 0.3−0.5) grown from gaseous chloride and hydride species is presented. A kinetic expression of the growth rate of ternary compounds is developed according to a statistical treatment of the adsorption and desorption fluxes of activated species within the frame of Eyrings theory. The kinetic model takes into account the internal energy of the elastic deformation. Growth rate features are then discussed with respect to the variations of the percentage of strain of the epilayers. It is shown that the growth rate increases with the strain percentage for a given composition for compressive systems, resulting from a preferential incorporation of the GaAs binary compound into the ternary solid phase. This behaviour is explained looking at the variations of the chemical potentials of formation of the elementary binary compounds which constitute the ternary phase, as a function of the elastic energy of deformation.

Self-doping near the seed/layer interface in conformal GaAs layers grown on Si

Undoped GaAs layers grown on Si substrates by the conformal method were studied by micro-Raman spectroscopy, cathodoluminescence, and diluted Sirtl solution with light (DSL) etching. The results show that nonintentional doping of conformal layers can take place near the seed/layer interface. The self-doped area presents a bright luminescence emission and shows longitudinal optic-plasmon coupled Raman modes. The nonintentional dopants were n type as deduced from Raman spectroscopy and DSL selective etching. The doped region extends only 2–3 μm from the seed and was tentatively associated with enhanced diffusion of Si in the presence of dislocations at the interface between the seed and the conformal layer.

Kinetic Modelling Of The Selective Epitaxy Of GaAs On Patterned Substrates By Hvpe. Application to the Conformal Growth Of Low Defect Density GaAs Layers On Silicon

The selective growth of GaAs by HVPE was studied on (001), (110), (111) Ga and (111) As , GaAs patterned substrates by varying the I1I/V ratio. A kinetic modelling of the growth was developed, based upon the SEM observations of the growth morphologies as well as on experimental curve synthesis. The growth rate is written as a function of the diffusion fluxes of the adsorbed AsGa and AsGaCI molecules and takes into account the chlorine desorption by H 2 . 1.5 μm thick GaAs films were then fabricated on Si (001) by a confined epitaxial lateral overgrowth technique. These conformal films exhibit intense and uniform luminescence signals, showing that the dislocation densities of GaAs are lower than 10 5 cm −2 . SEM analyses reveal that conformal growth fronts consist in (110) and (111) As A planes under the III/V ratios (superior to 1) which were tested.

Cathodoluminescence study of Si complex formation in self-doped and intentionally Si-doped GaAs conformal layers

An Si complex formation is observed in unintentionally doped as well as n-type doped GaAs layers grown laterally on GaAs seeds deposited on (100) Si substrates. The free carrier concentration was accurately assessed by previous Raman studies. Particularly interesting was the observation of a doped stripe nearby the GaAs seed in the unintentionally doped layers. In this work the formation of the complexes in both kinds of doped samples was analysed by means of SEM-cathodoluminescence (CL) studies. Different bands, indicative of the presence of more than one Si-related transition, have been observed in the infrared spectral region. The distribution of some of the related complexes at the different depths along the growth axis was analysed by depth-resolved CL. The nature of the emission levels has been investigated by power dependent CL studies, allowing to correlate them to DAP transitions. The Si autodoping origin of the doped stripes on the unintentionally doped samples was also confirmed.