J. G. Mihaychuk

Time-dependent second-harmonic generation from the Si–SiO 2 interface induced by charge transfer

We have observed that the second-harmonic signal generated from oxidized Si(001) varies on a time scale of several seconds in experiments involving a fundamental beam of lambda = 770 nm, 110-fs pulses at 76 MHz. We suggest that the temporal behavior arises from absorption of weak (<100-fW average power) third-harmonic light generated in air or in the sample, inducing charge transfer across the Si-SiO(2) interface and trapping in the oxide layer. Detrapping has been determined to take several minutes.

Determination of the crystallographic orientation of cubic media to high resolution using optical harmonic generation

Using the tensorial characteristic of optical harmonic generation it is shown that the crystallographic orientation of centrosymmetric and noncentrosymmetric cubic media can be determined to within ±0.1°. As an illustration of the technique the orientation of vicinal GaAs(001) and Si(111) single‐crystal wafers is obtained using second‐ and third‐harmonic generation, respectively, with a continuously mode‐locked Ti:sapphire laser operating at 775 nm. Intensity measurements were taken as a function of the wafer azimuthal angle and are fit to a truncated Fourier series derived from a phenomenological theory.

Magnesium surface segregation and its effect on the oxidation rate of the (111) surface of A1-1.45at%Mg

Abstract The temperature dependence of the surface segregation of magnesium onto the (111) surface of Al-1.45at%Mg and its subsequent effect on the oxygen adsorption rate have been studied using optical second harmonic (SH) generation. The SH intensity increases with Mg surface segregation up to 495 K but decreases at higher temperatures due to Mg evaporation. A bulk diffusion model for Mg segregation was found to be inconsistent with the data. Rather, the segregation rate was found to obey a simple one-dimensional nucleation and growth kinetic law with an activation energy of 7.2 ± 0.6 kcal/mol and a free energy for segregation of 4.9 ± 0.3 kcal/mol. The surface modified by the Mg segregation exhibits a sharp increase in the initial oxygen adsorption rate. This is consistent with a multi-site adsorption mechanism. At high annealing temperatures where the Mg surface concentration decreases due to evaporation, the oxygen adsorption rate also decreases. The initial sticking coefficient of the Mg-rich sites increases with Mg surface concentration; its maximum value is found to be of the order of unity, more than 10 times than that of the clean Al(111) surface.

Trapping and detrapping of electrons photoinjected from silicon to ultrathin SiO2 overlayers. I. In vacuum and in the presence of ambient oxygen

Transient trapping/detrapping of electrons at the Si(100)/SiO2 outer surface is studied studied in vacuum or with an O2 ambient (between 10−3 and 30 Torr) following internal electron photoemission from Si. Photoemission-current (produced by a 150 fs, 800 nm laser source) and contact-potential-difference techniques were used to investigate a wide variety of n- and p-doped samples at 300 K with thermally grown, steam grown, and dry oxides with thickness ⩽5 nm as well as samples with the oxide layers removed. Characteristics of the steam grown oxide were also studied at 400 and 200 K. For samples in vacuum charging is attributed to direct filling of at least two families of traps, one related to the oxide and the other the Si/SiO2 interface. For samples in O2, details of oxygen-assisted surface charging as reported previously [Phys. Rev. Lett. 77, 920 (1996)] are given. A fast, Coulomb-repulsion driven spillover of surface charge from the irradiated spot to the rest of the surface was detected. Oxygen aids t...

Transient charging and slow trapping in ultrathin SiO2 films on Si during electron bombardment

Surface charging and electron trapping in ultrathin (1.6 nm) SiO2 films on n-type silicon during bombardment by 350–600 eV electrons are observed by electric-field-induced optical second harmonic generation (SHG). Transient surface charging by fast dissipating electrons (<1 ms charge/discharge time) can be distinguished from oxide electron trapping occurring over hundreds of seconds. The maximum SHG enhancement corresponds to an areal density of trapped electrons of ∼6×1012 cm−2. The gradual recovery of the SHG following electron bombardment suggests the trap sites are “slow traps”, i.e., oxide traps which discharge via tunneling to the Si/SiO2 interface. The effective trap lifetime is about 500 s.

Addendum to ‘‘Determination of the crystallographic orientation of cubic media to high resolution using optical harmonic generation’’ [J. Appl. Phys. 74, 6072 (1993)]

Calculations of the optical harmonic response of cubic centrosymmetric and noncentrosymmetric media with arbitrary facial orientation are extended to the general case of s‐ or p‐polarized fun‐ damental beam radiation and s‐ or p‐polarized harmonic beam radiation.