SEMIINSULATING SUBSTRATE EFFECTS ON PURE GAAS EPILAYERS

Unintentionally doped GaAs layers were grown on semi-insulating GaAs s ubstrates by metal-organic chemical vapor deposition. Temperature-depe ndent electrical transport measurements were performed and the layer c haracteristics were derived by a two-layer analysis. The substrate beg ins to affect the layer transport properties at low temperatures, depe nding on the carrier density and the layer thickness. The p-type sampl es show two conductivity-type conversions at two different temperature s. One is a combined transport phenomenon of the layer and substrate, and the other occurs in the layer but is still influenced by the subst rate. A two-band model involving light- and heavy-hole bands was adopt ed in analyzing the hole transport in the layer, and the light hole wa s determined to play a crucial role even with its very small effective mass compared to the heavy hole.