M. Barbé

Model for heteroepitaxial growth of CdTe on (100) oriented GaAs substrate

A model is described, based on chemical bonding and lattice matching considerations, to account for the heteroepitaxy of CdTe on (100) GaAs substrate. The two main features of the proposed model are that the initial growth of CdTe starts with the formation of stable clusters of chemically bond Te, and that two types of cluster configurations are obtained depending only on the atomic structure of the (100)GaAs surface: the first one, made up of tetrahedral unit cells is formed on an As‐deficient surface and leads to (111) orientation, whereas the second one, formed by twin‐tetrahedral structures developed on an As‐ or Ga‐stabilized surface gives rise to (100) orientation.

Critical thickness in heteroepitaxial growth of zinc-blende semiconductor compounds

It is assumed that the critical layer thicknesses (CLT) in strained heteroepitaxial layers of zinc-blende semiconductor compounds depend on an energy balance relation between the strain energy and the deformation energy induced by the misfit dislocations. The first energy is evaluated by theoretical means and confirmed by calculation. In order to calculate the latter energy, we have developed an interfacial misfit dislocation model in association with a computer simulation method based on Keatings valence force field approximation. In this way the energy of the relaxed grown layer is obtained in the case of a complete network of two-dimensional misfit dislocations. The computer simulation results are compared with published experimental data. The predicted values are in excellent agreement with the experimental CLT measurements for CdTe on CdZnTe substrates as well as for GeSi on Si substrates, over the entire alloy compositional range. It is shown that the CLT depends in fact only on lattice mismatch η. The η-3/2 law of variation of the CLT found in this way may thus be considered as quite general and is extended to GaInAs/GaAs, GaSbAs/GaAs and GaInAs/InP systems.

Some fundamentals of the vapor and solution growth of ZnSe and ZnO

Abstract Some fundamentals of ZnSe and ZnO vapor and solution growth are investigated. Residual water present in gases or gaseous mixtures such as H 2 , Ar or H 2 +H 2 O is shown to act as a sublimation activator in the vapor-phase transport of both compounds. The processes involved in the growth by chemically activated sublimation with such gases and gas mixtures have been studied by close-spaced vapor transport (CSVT). The ZnSe growth rate is found to be constant, while in the ZnO case a high initial growth rate is followed by slower growth subsequently. Using a theoretical model, the thermodynamic constants of the transport – energies of activation, sublimation and condensation and enthalpy of formation – are determined independently from a fit to the variation of the growth rate as a function of the substrate temperature. No classical chemical transport reactions are shown to correspond to the sublimation mechanism, that is supposed to be chemically assisted by residual water. In the case of ZnO, the sublimation mechanism is found to be more complex than for ZnSe, as expressed by the variation of the growth rate with time. As an alternative to this chemically assisted sublimation, chemical vapor transport using chlorine as chemical agent is proposed for ZnO. Significant transport is found to occur at temperatures of about 1000°C. Concerning solution-growth, the pseudo-binary PbCl 2 –ZnO phase diagram established by differential thermal analysis (DTA) shows PbCl 2 to be a good solvent of ZnO, as for ZnSe. Zn–In alloys are proposed as good alternative solvents for ZnO not having the great reactivity of the PbCl 2 –ZnO mixture with silica.

Carbon acceptor doping efficiency in GaAs grown by metalorganic chemical vapor deposition

Carbon doping efficiency in GaAs grown by metalorganic chemical vapor deposition using intrinsic and extrinsic doping sources is studied. Independent of the carbon source, carbon hydrogen complexes are systematically present and depending on the growth conditions, carbon dimers can be present and form complexes with hydrogen as well. Carbon–hydrogen related complexes and dimers reduce the hole concentration decreasing the doping efficiency. Additionally, the carbon dimer introduces a deep level, decreases the hole mobility and hydrogen bonds stronger to it than to isolated carbon. Depending on the growth conditions it is possible to reach 100% doping efficiency with high hole mobility.

ZnO growth by chemically assisted sublimation

Abstract Residual water present in gases or gaseous mixtures such as H 2 , Ar or H 2 + H 2 O is shown to act as sublimation activator of the vapour phase transport of ZnO. The thermodynamic constants of the water activated sublimation are determined through close spacing vapour transport experiments using a theoretical model. The variation of the growth rate as a function of temperature is found to be not linear. Finally, some optical and structural properties of the layers are studied and compared to those of bulk crystals. No photoluminescence emission that could be attributed to HO or O 2 are detected.

Setting up of misfit dislocations in heteroepitaxial growth and critical thicknesses

In a previous work we have shown that the critical layer thickness (CLT) in heteroepitaxial growth of zinc-blende semiconductor compounds, as defined by the minimal energy configuration between the coherent deformation of the layer and the full misfit dislocation (MD) system, varies clearly only with the lattice mismatch η as η−32. We report new results regarding situations defined mainly by the fact that the MD array is, as often observed experimentally, not complete in length or in density. In the simplest case the interfacial MD have a maximum length but only along one direction and the layer is partially relaxed, with a strain energy roughly linear as a function of thickness. Pseudo CLT are found to be smaller than the one of a completely relaxed layer. In the situation of an incomplete interfacial cross-shaped MD, dislocation loops with threading dislocation (TD) lines are assumed and the system involves strain energy value always higher than that of a full MD system. It is shown that the setting up of the full MD system is not progressive but is rather a brutal one, as in a phase transition. Another observation is that partial MD systems lead to apparent CLT different from a complete MD network. In the case of low density MD array, i.e. with MD infinite in length and located at various distances from each other, stepped stages in the setting up of the total system are also found when varying the array density. The apparent CLT are submitted to change from 0.7tc up to 1.4tc, where tc is the equilibrium CLT in an ideal unit cell. Phenomenological models are proposed with results which are in good agreement with the computational data.

Carbon reactivation kinetics in GaAs: Its dependence on dopant precursor, doping level, and layer thickness

The reactivation kinetics of the acceptor behavior of carbon, its dependence on dopant precursors, doping level, layer thickness, and annealing temperature, as well as the behavior of carbon-hydrogen complexes in GaAs grown by metalorganic chemical vapor deposition are studied. Independent of the carbon source, in the “as grown” material, systematically carbon hydrogen complexes are present and the hole concentration is lower than the corresponding carbon concentration. The carbon reactivation kinetics was achieved by ex situ rapid thermal annealing through a series of multistage annealing experiments and assessed at each annealing stage by infrared absorption, hydrogen secondary ion mass spectroscopy profiling, and hole concentration measurements. Carbon reactivation occurs solely by the debonding of hydrogen from the isolated carbon acceptor and its out-diffusion from the sample. The carbon reactivation kinetics can be treated as a first order one with an activation energy, Ea=1.42±0.01 eV, independent ...

Deuterium passivation of electrically active defects in nonintentionally doped n-GaN

Deuterium diffusion was achieved in nonintentionally doped n-GaN layers, grown by metal organic chemical vapor deposition, at 460°C and a power density of 1.0Wcm−2. A deuterium diffusion mechanism was observed yielding concentrations around 1018cm−3 in the surface region following the (Dt)1∕2 diffusion law. A second mechanism displaying an abnormally high diffusion coefficient, probably occurring along threading dislocations, was observed. The fast diffusing deuterium traps electrons and passivates residual acceptors, decreasing the electron concentration from 1016to1015cm−3 and increasing the electron mobility from 10to320cm2V−1s−1, producing better material for electronic devices.

Effect of Deuterium Diffusion on the Electrical Properties of AlGaN/GaN Heterostructures

We have studied the influence of a deuterium diffusion on the electrical characteristics of the 2D gas present in AlGaN/GaN heterostructures. The deuterium diffusion is performed by exposing the structures to a rf remote deuterium plasma. We find that both the sheet carrier concentration and the electron mobility decrease and that these effects are partly reversible under thermal annealing. These results suggest that deuterium behave as acceptors in the 2D gas region. The negatively charged deuterium act as additional scattering centers for electrons.

Study of the chemically activated sublimation of ZnSe

Abstract The reactions and processes involved in the growth of ZnSe by chemically activated sublimation in a H 2 atmosphere are studied. The rate of transport as a function of source and substrate temperatures and the difference between them are determined from close spacing vapour transport experiments. According to this process, ZnSe layers are deposited on sapphire substrates by short distance chemically assisted sublimation. The experimental results are analysed and the thermodynamic constants of the transport are determined using a theoretical model for kinetically controlled processes, assuming water to act as sublimation catalyst. A preliminary optical and structural characterisation of the layers has also been performed.