Barrier Height in Indirect Bandgap AlGaAs/GaAs Hetero-Junction Determined with n-Semiconductor/Insulator/Semiconductor Diodes

Electron transport through the GaAs/Al_xGa_1-xAs/GaAs n-semiconductor/insulator/semiconductor diodes (x>0.45) is studied to clarify the valley which determines current conduction. The potential barrier for thermionic emission current was shown to be determined by the X valley of AlGaAs in the indirect bandgap region. It was also directly shown that conduction band discontinuity decreases when increasing the Al mole fraction of AlGaAs layer beyond the band cross over point. The most suitable Al mole fraction of undoped AlGaAs used as the gate insulator of n-channel GaAs MISFETs is concluded to be about 0.45.