Characterization of GaAs layers grown on polycrystalline GaAs by LPE and current controlled LPE

It is the purpose of this paper to investigate the suitability and effectiveness of growth of thin GaAs layers on polycrystalline GaAs substrates by liquid phase epitaxy (LPE) and current controlled LPE (CCLPE). During each growth run LPE and CCLPE were used to grow thin GaAs layers on two large-grain polycrystalline GaAs substrates cut from the same wafer and simultaneously placed in the same growth system. The grain boundary was exposed by cleaving the samples perpendicular to the grain boundary. Notnarski contrast, SEM, C-V and Hall measurements were performed in order to determine the surface morphology, discontinuity of epilayer at the grain boundary, epilayer thickness unform-ity, resistivity (in directions parallel and perpendicular to the grain boundary), and dopant concentration. The CCLPE system was carefully designed so that growth would take place only by electrotransport in the absence of convection or Peltier cooling. The results indicate that CCLPE yields layers with improved surface morphology and thickness uniformity as compared to those grown by LPE. In some samples the epilayer was discontinuous at certain grain boundaries. Results are presented on CCLPE growth rate dependence upon grain orientation, current density, and continuity of the epilayer at the grain boundary.     

Selective etch-back and growth of InGaAs ON (100) Fe:lnP by electroepitaxy

Selective etch-back prior to growth of InGaAs islands on SiO₂-masked (100)Fe-doped InP substrates was performed by electroepitaxy. The etch-back of the substrate and the growth of the layer was done at a constant furnace temperature of 640° C by passing a direct electric current from the melt to the substrate for etch-back and from the substrate to the melt for growth. The current density used was 1 to 20 A/cm² for a period from 15 to 60 min. The isolated InP regions were of various sizes (40 × 1000μm to 3000 × 3000μm), and different geometries (narrow and wide strips, square, circular). A uniform etch-back and uniform growth with excellent surface morphology was obtained on strips as wide as 200μm and on circles withd < 500μm. For islands with wider geometry, growth as well as etch-back were uniform up to 100–200μm from the periphery with excellent surface morphology. The etch-back and growth profiles are trapezoid-shaped and are not influenced by the difference in chemical activity between crystalline planes. The orientation dependence of the etch rate was {110} > {100} > {011} > {111} B > {111} A.     

Current controlled liquid phase epitaxial (CCLPE) growth of InGaAs on (100) InP

High quality epitaxial layers of In_xGa_1−xAs (x = 0.53) were grown on semi-insulating (Fe-doped) (100) InP sub-strates. The layers were grown at a constant furnace temperature of 640°C by passing a direct electric current (0–10A/cm²) from the substrate to the melt. In order to minimize the out-diffusion of Fe atoms from the bulk of the substrate during the melt saturation, the substrate was kept at a cold temperature region (340°C) within the growth chamber and remotely loaded in the graphite boat just prior to the initiation of the growth cycle. In addition to pre-venting the out-diffusion of Fe atoms, this procedure sub-stantially reduced the thermal degradation of the InP sub-strate surface. The above technique produced high quality layers having uniform thickness and good surface morphology. A study of the dependence of growth rate on the applied current density yielded an average growth rate of 0.06μm/ A-min. Room temperature Hall measurements on layers grown by CCLPE resulted in Hall mobilities μ₃₀₀ = 8900cm²/V-sec at a carrier concentration of 6.2 × l0¹⁶cm⁻³. The improve-ment in the mobility achieved by the CCLPE technique is attributed to a reduced out-diffusion of scattering centers from the substrate into the growth layer, as well as to the higher quality of epitaxial layers normally achieved by CCLPE.