Dependence of apparent barrier height on barrier thickness for perpendicular transport in AlAs/GaAs single-barrier structures grown by molecular beam epitaxy

Current-voltage characteristics of single-barrier AlAs/GaAs heterostructures measured over a wide temperature range are used to elucidate the mechanisms governing electron transport through these barriers. Five barriers, ranging in thickness from 14.2 to 150 Å, are examined. The results clearly illustrate Γ-band, elastic-tunneling-dominated transport for the thinnest barrier (14.2 Å) devices and thermionic emission characteristics for the thickest barrier (150 Å) devices. However, devices with an intermediate barrier thickness exhibited tunneling-like currents larger than calculated low-temperature elastic tunneling currents. This effect is apparently due to inelastic tunneling from the GaAs Γ band through the AlAs X-point barrier.