PERPENDICULAR TRANSPORT MEASUREMENTS IN GaAs/(Al,Ga)As/GaAs HETEROSTRUCTURES.

Summary form only given. The temperature dependence of the current-voltage characteristics of n** plus -GaAs/i-(Al, Ga)As/n**- GaAs barrier structures has been examined in both the thermionic and thermionic-field emission regimes. These structures had Al mole fractions between 0. 40 and 0. 60, with a barrier thickness of 300 angstrom. The activation energy for electron transport from the n** plus -GaAs layer through the (Al,Ga)As layer has been measured by analysis of the experimental data with standard thermionic emission theory. The conduction band discontinuity increased from 350 mV at 40% Al to almost 400 mV at 50% Al, and then decreased to 320 mV at 60% Al. The peak value is significantly higher than the maximum value which had been previously predicted. These results also suggest that the direct/indirect crossover for electron transport occurs at an Al mole fraction close to 50%, much higher than the crossover composition determined from optical data ( approximately equals 40%) on well-characterized bulk (Al, Ga) As material.