Length dependence of quantized conductance in ballistic constrictions fabricated on InAs/AlSb quantum wells

A length-dependent analysis of quantized conductance in split-gate constrictions fabricated on InAs/AlSb quantum-well heterostructures is presented. Conductance steps with spacing within a few percent of 2e(2)/h are observed in constrictions with channel lengths of 0.2 mu m. With increasing constriction length nearly ideal quantized conductance can still be observed, even in constrictions as long as 2.0 mu m. The values of the quantized step heights are found to vary more from device to device with increasing length. Our length-dependent data differ considerably from previous reports on GaAs/AlxGa1-xAs split-gate devices where the quantized conductance was severely degraded for constriction lengths greater than or similar to 0.6 mu m. Temperature-dependent measurements indicate that the 2.0-mu m-long devices have one-dimensional (1D) subband spacings close to 10 meV. The improved length performance of our devices is believed to be due primarily to the increased 1D subband spacings relative to the magnitude of potential fluctuations in the channel region. Our explanation is shown to be in agreement with recent theoretical analyses relating various scattering mechanisms to the breakdown of quantized conductance.