Two-color optical technique for characterization of x-ray radiation-enhanced electron transport in SiO2

Abstract

Damage enhanced electron transport, across thin oxides in x-ray irradiated Si/SiO 2 samples, was measured via a contactless two-color laser technique. This method involves two steps: ͑1͒ optically stimulated electron injection into the oxide and ͑2͒ detection of transport, trapping, and recombination rates using time-dependent electric-field-induced second-harmonic generation arising from charge separation at the interface. Measured electron transport rates across an irradiated oxide are found to be substantially higher in comparison to unirradiated oxides. This effect is attributed to the presence of x-ray irradiation-induced defects that act as intermediate trapping sites facilitating enhanced electron tunneling through the oxide. The possible nature of the radiation-induced trapping sites is discussed.

Contactless ultra-fast laser probing of radiation-induced leakage current in ultra-thin oxides

“…3(b), curves b-d], indicating an increase in electron transport from the free surface back to the substrate. Hence, the X-ray radiation-induced defects in the are seen to greatly enhance conduction current through these thin oxides [4], [13]. In Fig.…”

“…is the charge dissipation time due to tunneling and subsequent recombination with holes at the interface [4]; and is the time-dependent function that equals 1 in the first experimental mode (shutter not blocking the laser beam) and 0 in second experimental mode (shutter blocking the laser beam).…”

“…As gate oxides become thinner than 3 nm, direct quantum mechanical tunneling through the dielectric barrier is found by electrical measurements to be the dominant contribution to leakage current. This type of radiation-induced leakage current (RILC) is often attributed to an inelastic tunneling process, mediated by radiation-induced neutral traps in the oxide [3], [4].…”

Spin/carrier dynamics at semiconductor interfaces using intense, tunable, ultra‐fast lasers

“…Presently, characterization of radiation damage in Si/SiO 2 systems is usually accomplished with electrical methods such as capacitance-voltage (C-V) and current-voltage (I-V) measurements. We use a novel two-color technique, based on time-dependent electric field induced SHG, for direct measurements of changes in electron transport characteristics due to X-ray irradiation in thin oxides to characterize the radiation response of a 42 Å SiO 2 film on Si(100) [13]. We find that the detrapping rate of surface charge in the X-ray irradiated devices is much higher than that of unirradiated devices.…”

Noninvasive and Contactless Characterization of Electronic Properties at the Semiconductor/Dielectric Interface Using Optical Second-Harmonic Generation

“…The SHG process involves doubling the frequency of incident light as a nonlinear medium converts the cumulative energy of two incident photons into a single photon. − In a centrosymmetric material, nonlinearity arises as the symmetry breaks at the material surface or its interface with another material. The nonlinear response is typically limited to the first atomic layer (occasionally second or third atomic layer) from the material surface or interface. ,, In the last two decades, significant efforts have been directed to studying electron dynamics at the technologically crucial silicon/silicon dioxide (Si/SiO 2 ) interface using optical SHG. − ,,− ,− Despite these, a quantitative characterization of electronic properties at the semiconductor/insulator interface using optical metrology has yet to be accomplished. The following noninvasive and contactless SHG-based metrology method has been developed for the complete quantitative characterization of the electronic properties at the insulator–semiconductor interface.…”