Radiation-enhanced self- and boron diffusion in germanium

Abstract

We report experiments on proton irradiation enhanced self-and boron (B) diffusion in germanium (Ge) for temperatures between 515 • C and 720 • C. Modeling of the experimental diffusion profiles measured by means of secondary ion mass spectrometry is achieved on the basis of the Frenkel pair reaction and the interstitialcy and dissociative diffusion mechanisms. The numerical simulations ascertain concentrations of Ge interstitials and B-interstitial pairs that deviate by several orders of magnitude from their thermal equilibrium values. The dominance of self-interstitial related defects under irradiation leads to an enhanced self-and B diffusion in Ge. Analysis of the experimental profiles yields data for the diffusion of self-interstitials (I) and the thermal equilibrium concentration of BI pairs in Ge. The temperature dependence of these quantities provides the migration enthalpy of I and formation enthalpy of BI that are compared with recent results of atomistic calculations. The behavior of self-and B diffusion in Ge under concurrent annealing and irradiation is strongly affected by the property of the Ge surface to hinder the annihilation of self-interstitials. The limited annihilation efficiency of the Ge surface can be caused by donor-type surface states favored under vacuum annealing but the physical origin remains unsolved.

Diffusion ofn-type dopants in germanium

“…Whereas the diffusion of self-and B-atoms is clearly enhanced compared to thermal equilibrium conditions, the diffusion of n-type dopants such as P and As remains unaffected, i.e., equals the diffusion under thermal equilibrium conditions. 72,145,146 In Ref. 145, a retarded diffusion of P under irradiation is reported, which is at variance with the results presented in this work and more recently in Ref.…”

“…72 The theoretical prediction of 1.2 eV reported by Carvalho et al 71 is in acceptable agreement with the experimental value.…”

“…Concentration profile of 74 Ge (þ) measured with secondary ion mass spectrometry after annealing a ( nat Ge/ 70 Ge) 10 isotope multilayer structure at 587 C for 5400 s and concurrent irradiation with 2.5 MeV protons at a flux of 1 lA. The green solid line represents the best fit to the experimental 74 Ge profile based on the model for Ge self-diffusion under irradiation proposed by Schneider et al 72 The calculated concentrations of V and I normalized to their thermal equilibrium values are referred to the right axis. The distributions of both V and I are homogeneous with V concentrations close to thermal equilibrium and I concentrations in high supersaturation.…”

“…The effect of proton irradiation on self-and dopant diffusion in Ge was recently studied by means of isotopically controlled Ge and natural Ge samples doped with P, As, and B. 72,145,146 Analysis of self-and dopant diffusion in Ge under irradiation revealed a surprising diffusion behavior. This is demonstrated by Figs.…”

“…The B profiles reveal a stronger diffusional broadening at low compared to high temperatures. The solid lines are theoretical B profiles calculated on the basis of the B diffusion model described by Schneider et al 72 The model considers contributions of substitutional B s , BI pairs, and immobile B clusters to the total B concentration. evident.…”