J. Napierala

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.

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.

Study of defects in conformal GaAs/Si layers by optical techniques and photoetching

We present the characterization of crystal defects in GaAs layers grown on silicon substrates by the conformal growth method. This technique consists of GaAs lateral growth from GaAs seeds confined in between the Si substrate and an overhanging dielectric cap layer. These conformal layers grow with a reduced density of crystal defects, e.g. dislocations, which are effectively filtered by the particular geometrical configuration. The samples were analyzed by micro-Raman spectroscopy, cathodoluminescence, phase stepping microscopy and were etched by diluted stirl solution applied with light (DSL). Several structures were revealed and analyzed, e.g. a quasi-periodic array of hillocks and valleys that are spatially correlated with fluctuations of the luminescence intensity. Other revealed crystal defects were grooves, hillocks and cracks. The main properties of these defects and their possible origin are studied.

Conformal MOVPE of (Al)GaAs on silicon using alternative chlorine-containing precursors

GaAs and AlGaAs were deposited on silicon for the first time using conformal MOVPE growth, a lateral epitaxial overgrowth technique. Since this method requires selective growth, the chlorine-containing precursors dimethylgallium-chloride (DMGaCI) and dimethylaluminumchloride (DMAlCl) were used to prevent polycrystalline nucleations on the dielectric mask and the silicon substrate. The vapor pressures of these precursors have been determined. Several precursors for doping (hydrogen sulfide (H 2 S), diethylzinc (DEZn), carbontetrabromide (CBr4)) were tested together with the chlorine-containing precursors. Microphotoluminescence (μ-PL) and cathodoluminescence (CL) measurements were carried out on the conformal (Al)GaAs structures to determine the extension of the conformal layers. SEM pictures reveal the shape of the growth front.

Study of doping in GaAs layers by local probe techniques: micro-Raman, micro-photoluminescence and cathodoluminescence

The free carrier concentration of GaAs layers grown by MOCVD either on GaAs or Si substrates, by the conformal method in the last case, was obtained from the micro-Raman spectra using the hydrodynamic approach to fit the LO phonon-plasmon coupled Raman modes. The results on homoepitaxial layers were used as a calibration of the fitting method. The measurements in the selectively doped conformal layers were then compared with data obtained by micro-photoluminescence and cathodoluminescence spectroscopy and imaging. The doping data are compared with those deduced from the room temperature micro-photoluminescence and cathodolumiescence spectra.

Doping profiles of n-type GaAs layers grown on Si by the conformal method

Abstract : We study doping profiles in selectively Si-doped GaAs layers grown by the conformal method, This growth technique allows to obtain GaAs/Si with optoelectronic quality. The samples are laterally grown, and selective doping with Si is carried out in such a way that doped stripes are intercalated with undoped ones. The study of the doping profiles was carried out by cathodoluminescence (CL) and micro-Raman (Micro-R) spectroscopy. Abrupt doping profiles between doped and undoped stripes were demonstrated by monochromatic CL images. Deep level related CL bands can be observed between 1000 and 1400 nm, evidencing the complex mechanism for Si incorporation at the growth temperature (730 deg C). Net doping concentrations and mobilities across the layers were determined from the analysis of the phonon-plasmon coupled modes in the Micro-R spectra obtained with a lateral resolution better than 1 micrometer.