Direct tunneling of electrons in Al-n ~+-Si-SiO_2-n-Si structures under conditions of nonstationary depletion of the semiconductor surface of the majority charge carriers

摘要

Specific features of direct tunneling of electrons through an ultrathin (~40 ?) oxide in metal-SiO_2-Si structures under nonstationary conditions of depletion of the semiconductor surface, in which case the potential relief in the insulator is only slightly perturbed by external electric fields, have been experimentally studied. Penetrability of the tunneling barrier is appreciably limited by a classically forbidden region in n-Si (this region is brought about by fixed negative charge in SiO_2). As the voltage drop across oxide is increased, the electrons localized within this oxide transfer to the semiconductor, which is accompanied by a drastic increase in the tunneling current. The values of coefficients linear rise in the logarithm of tunneling current as the voltage at the isolator is increased are determined from the experiment. These values are not consistent with the data calculated on the basis of a model of a rectangular barrier with parameters typical of "thick" oxides. It is shown that actual values of the effective mass are bound to be larger than 0.5m_0, while the height of the barrier is bound to be lower than 3.1 eV.