LPE-growth of InP on GaAs

LPE growth of InP on GaAs is shown to be possible from indium or tin as a solvent, respectively. Only growth on (1 1 1 ) B faces yields acceptable smooth layers. From In/InP-melts layers with inclusions near the heterojunctions are obtained. No such microscopically small inclusions were observed in layers grown from Sn/InP-melts. – The grown layers were characterized by means of etching and electron beam microprobe analysis.     

Zum Wachstum von AIIIBV-Halbleitern aus nichtstöchiometrischen Schmelzen (II) Dotierung von GaAs und Ga1−xAlxAs mit Zink

Doping of GaAs and Ga_1−xAl_xAs with Zn in the LPE process was studied by a radioanalytical method. It is found that Zn diffuses from the Ga-(Al)-As-Zn-solution into the n-GaAs substrate before epitaxial growth starts. This “pre-diffusion” and the following diffusion of Zn out of the epitaxial layer into the substrate results in three regions with distinct Zn-graduation in the vicinity of the pn-junction. There are no striking differences for GaAs/GaAs and Ga_1−xAl_xAs/GaAs structures. The Zn concentration in GaAs epitaxial layers decreases exponentially from the substrate up to the layer surface. From this profile the temperature dependence of the Zn segregation coefficient is calculated. At 900°C a value k_eff = 5,2 · 10⁻² is found. The doping profile in Ga_1−xAl/As layers is more complex. It is influenced by the changings of temperature during the growth of the layer and by the nonuniform Aldistribution over the layer thickness.     

New prospects for “living” anionic polymerization of (meth) acrylic esters

The living low temperature polymerization in polar solvents of most methacrylates, even functional ones, can now be performed by direct and experimentally convenient anionic methods, thanks to the use of α-methylstyrene and of complex-purified monomers. A diversified family of block copolymers has thus been generated, that are used as compatibilizing agents in the designing of interesting heterophase materials: i.e. blends of polymers and inorganic fillers, and liquid-solid dispersions. The living polymerization of acrylates (or of methacrylates under more drastic conditions) raises additional requirements: they have been met to a large extent by the use of specific ligands of the growing ion-pair. Resulting structures such as f.i. block copolymers and end-functionalized oligomers of a low dispersity, should have a great interest in the molecular engineering of (meth)acrylate-based products. Finally, these new initiators lend themselves to structural and mechanistic studies which should shed some light on the critical features of these living propagation processes.     

Band tail conduction in Zn-doped GaAs

The electrical parameters of Zn-doped GaAs liquid phase epitaxial layers are determined in the temperature range from 77 to 300 K by Hall effect and resistivity measurements. An analysis of the experimental data yields an ionization energy of 30.4 meV for the Zn acceptor in GaAs in the dilute limit of acceptor concentration. For the Mott transition a critical hole concentration of about 6 · 10¹⁷ cm⁻³ is estimated. It is found that the temperature dependence of the electrical parameters is essentially influenced by band tail conduction effects at doping levels above the Mott transition.     

Thermodynamic Calculation of the Alloy Composition of GaxIn1−xAs Grown in the Trichloride System Using Solid Sources

The dependence of the Ga_xIn_1−xAs alloy composition as a function of the experimental input variables is calculated for a growth system using AsCl₃ and solid GaAs and InAs sources. The results are similar to those earlier obtained for growth in the hydride system. Additional AsCl₃ introduced downstream the source regions shifts the alloy composition towards higher GaAs content.