Nonavalanche injection of hot carriers into SiO2

Carriers can be injected into the SiO2 from a junction reverse biased below avalanche and lying in the silicon near the Si–SiO2 interface. This effect was studied for electron injection in n-channel MOS transistors. The electrons originated from a forward-biased (supply) junction lying below the source, drain, and channel region. The electrons were heated in the space-charge layers of source and drain reverse biased below avalanche breakdown and in the space-charge layer below the channel induced by the combined effect of a positive gate voltage and the reverse bias on source and drain. Injection into the oxide occurs mainly from the latter region. The current through the oxide and the charge trapped in the oxide were measured as a function of several parameters. These measurements yield the threshold values of the reverse source (drain) voltage, VTR, and of the gate voltage, VGT, necessary for injection. From the dependence of VTR on the concentration of dopant in the channel region, the value of the mean free path λ of hot electrons between inelastic phonon collisions in the silicon is estimated as 125 Å. The method presented may be a powerful tool for studying these collisions in other semiconductor materials. The injection of holes into the SiO2 was possible by virtue of the same nonavalanche mechanism. Some results are given of measurements in a slice with p-channel MOS transistors.