An atomic force microscope-based investigation of vertical transport through GaAs/GaAlAs/InAlAs/GaAs step-barrier heterostructures

Study of vertical transport through heterostructures consisting of single, double, or multiple quantum barriers is of both fundamental and technological interest. While extensive data regarding electron transport is available for single- and double-barrier structures, relatively less information is available for transport through step-barrier structures. In this paper, we present results from a study of room temperature vertical transport through a GaAs/GaAlAs/InAlAs/GaAs multistep-barrier heterostructure. A typical atomic force microscope has been adapted to perform transport measurements, thus allowing precise control of the physical location of the region of measurement. I-V measurements reveal negative differential resistance (NDR) peaks, thus confirming the formation of resonant states in a triangular well created when a voltage bias is applied across the step barrier. I-V curves have also been calculated by numerically solving the Schrödinger wave equation for this step-barrier structure. Comparison between the measured and calculated I-V curves shows reasonable agreement in the number of NDR peaks. However, discrepancies exist between the measured and calculated values for the voltages at which these NDR peaks occur. Some possible reasons for these discrepancies are discussed in this work.