Electron Beam Doping by Superdiffusion in Unirradiated Regions (X<300 Å) of Semiconductors at Room Temperature

Abstract

Electron beam doping processes in the damageless region and at room temperature were investigated before annealing. In the three-layer system of layer 3/layer 2/layer 1, the impurity sheet (layer 2) was sandwiched between two semiconductor wafers. The surface of layer 3 was irradiated with electron beams of 750 keV and 7 MeV. Interstitials of displaced atoms in the overlayer, which were introduced by irradiation, migrated to the surface of the semiconductors. These interstitials diffused rapidly at the surface with a very large surface diffusivity of ∼10-5 cm2· s-1. The diffusion process was observed using an atomic force microscope (AFM). Impurity concentrations in the surface layer during irradiation were found to be on the order of matrix atom concentration. Electron irradiation produced a number of self-interstitials that migrated with large surface diffusivities at the surface. Diffusion was enhanced due to the kick-out mechanism at the interface of the system and in the depth direction of the semiconductors.

Superdiffusion of impurity atoms in damage‐free regions of semiconductors

“…However, Si atoms are doped into the GaAs layer 1 and occupy As sites as indicated by the PL spectra. Furthermore, the surface concentration of EB-doped impurities in the GaAs layer 1 for the GaAs/Si//Si/GaAs system is around 100 times higher than that for GaAs//Si//GaAs [22]. As the diffusivity of Si atoms at the interface between the GaAs wafer and the overlying Si layer is considered to be very small in EBD, the surface diffusion of interstitial or displaced atoms is believed to be dominant in this case as reported previously [28].…”

“…In EBD, we can therefore consider the following: (i) electron irradiation creates Frenkel defects and electron-hole pairs in the substrate [28]; (ii) the theoretical energy spectra of the primary displaced atoms can be obtained as a function of the average energy transfer [22,29]; (iii) the migration energy of interstitials is small (0 -0.22 eV for Si [22,30]; (iv) the surface diffusivities of impurities are of the order of 10 10 times larger than the volume diffusivities; (v) there are two kinds of kick-out mechanisms [31][32][33].…”

“…4 as a function of depth from the irradiated surface. The displaced atoms do not create new ones, because their average energies (0-8 eV) are lower than their threshold energies (9.2 eV) for atomic displacement [22]. The total numbers of Ga displaced atoms in GaAs introduced with an electron fluence of ~5 × 10 17 cm -2 at 750 keV was found to be 4.74 × 10 14 atoms/cm 2 .…”

“…The energy spectra of electrons at different depth in GaAs and Si for incident electron energies of 750 keV were calculated [21]. The results were obtained by using Sugiyama's program [35] for a Monte Carlo simulation for the theory of fast electron penetration in matter [22]. The program took account of multiple scattering of electrons, straggling of electron energy losses by ionization and excitation of atoms, production of knock-on electrons, and bremsstrahlung photons.…”

“…As part of ongoing research into enhanced diffusion, Wada et al [7 -9] in a study on ntype germanium reported that the Hall coefficient in a 110 µm thick layer of the material changes from negative to positive at a depth of about 50 µm after exposure to an electron beam with total flux of 10 16 electrons/cm 2 at 7 MeV. Electron beam doping (EBD), first proposed by Wada [7][8][9][10], has been further developed by the present authors [11][12][13][14][15][16][17][18][19][20][21][22][23][24]. In the present paper, the effects of fine superdiffusion process was studied for three-layer structure.…”