ELECTRICAL-PROPERTIES OF N-GAAS EPILAYERS, FET AND HEMT STRUCTURES GROWN ON LT-GAAS BY MBE

We have investigated the dependence of the conductive layer width and Hall mobility in n-GaAs/LT-GaAs structures on the conditions of low te mperature (LT) buffer growth and on annealing parameters. Both the con ductive layer width, as determined from electrochemical C-V profiling, as well as the carrier mobility of the doped epilayer decrease as the LT-GaAs growth temperature is reduced and decrease with duration and temperature of annealing. This degradation is attributed to the outdif fusion of excess arsenic and the formation of arsenic precipitates in the n-GaAs epilayer and to the outdiffusion of point defects, as indic ated by Photoluminescence observations. The use of AlxGa1-xAs/GaAs sup erlattice and GaAs as intermediate layers between the LT buffer and th e active layers in field effect transistor (FET) and high electron mob ility transistor (HEMT) structures results in maintaining both carrier mobility and doping profile at conventional layer levels. The improve ment is attributed to the suppression of excess As and point defect ou tdiffusion from the LT-GaAs to the active layer. (C) 1997 Elsevier Sci ence S.A.