A thermodynamical model of molecular beam epitaxy, application to the growth of II VI semiconductors
We present a model of molecular beam epitaxy based on thermodynamics. The equilibrium between a compound or a ternary alloy with the gas phase is illustrated in the case of HgTe and CdHgTe. The meaning of equilibrium pressure is analysed and we make the assumption that the fluxes leaving the actual growing compound are linked by the mass action law where the pressures are transformed into the equivalent fluxes. A detailed balance of the species leaving or arriving at the surface is then possible and leads to a set of equations which can be solved to predict the growth rate, the x value of a ternary alloy, the excess of one of the species, the incorporation coefficient. Examples of calculation are shown for CdTe and Cd x Hg 1−x Te and are compared with experimental results and show a good agreement. The main interest of this model resides in its ability to predict the effects of the modification of one of the growth parameter. Nevertheless it predicts only the limit conditions which are not necessary reach due to the kinetic of the reactions Presentation d'un modele thermodynamique de l'epitaxie par jets moleculaires. Illustration par les cas de HgTe et CdHgTe. La comparaison avec les resultats experimentaux montre la validite des previsions du modele, dont l'interet principal est de permettre d'evaluer l'influence de la modification d'un parametre de croissance. La validite de ce modele est cependant limitee si la cinetique des reactions ne permet pas d'atteindre l'equilibre; ce n'est pas le cas pour les alliages II-VI etudies ici
Characterization of CdxHg1-xTe p-type layers grown by MBE
CdxHg1-xTe layers have been grown onto CdTe(111) orientation substrates between 160 and 180°C using Cd, Te and Hg cells. With growth rates ∽4 μmh-1, the films present a good crystallinity and an interdiffusion depth substrate/layer smaller than those achieved by other techniques. For the first time it is shown that p-type layers suitable for device applications can be achieved by MBE. It is also demonstrated that p-type or n-type can be selected either by a change in the substance temperature or by a modification of the Hg flux value.
Transport properties of Sn‐doped AlxGa1−xAs grown by molecular beam epitaxy
Transport properties of Alx Ga1−x As layers having AlAs mole fractions between 0.17 and 0.375 and grown by molecular beam epitaxy were investigated. The Al cell temperature was kept at 1075 °C while the Ga cell temperature was changed between 910 and 950 °C to obtain the aforementioned AlAs mole fractions. The donor levels of Sn in Alx Ga1−x As obtained from the temperature dependence of the net donor concentration are below 3, 30, and 40 meV for x=0.17, x=0.29, and x=0.375, respectively. Al0.22 Ga0.78 As layers having a net electron concentration of about 1.7×1018 cm−3 and grown at 630 °C exhibited a mobility of 868 and 1095 cm2/V sec at 300 and 78 °K, respectively. The mobility was found to be strongly dependent on the substrate temperature during the growth. The lower substrate temperatures resulted in lower electron mobility.