Tunnelling current analysis of GaAs n ⁺⁺-p ⁺⁺-n ⁺⁺ ultrathin barrier structures grown by molecular layer epitaxy

The tunnelling probability for GaAs n ⁺⁺-p ⁺⁺-n ⁺⁺ ultrathin barrier (UTB) structures is calculated based on the parabolic barrier model by using the WKB approximation. The calculated tunnelling current for the UTB structure with a 45 angstrom p ⁺⁺ layer grown by molecular layer epitaxy is in good agreement with the experimental data at room temperature and 77K. This indicates that the MLE-grown epitaxial layers have sufficient crystal quality and such parameters as doping concentrations and layer thickness are well controlled. The effective tunnelling width at zero bias is about 97 angstrom, which is much smaller than the measured depletion width 190 angstrom by the C-V method. The depletion width by the C-V method cannot be used to estimate the tunnelling current in UTB devices. The results obtained may be applied to the design of ballistic tunnelling devices.