Generation of divacancies in silicon irradiated by 2-MeV electrons: Depth and dose dependence

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Abstract
Czochralski‐grown silicon samples (n‐type) have been irradiated by 2‐MeV electrons at room temperature to doses in the range of 1015–1016 cm−2. The generation of divacancies (V2) has been studied as a function of bombardment dose and sample depth using deep‐level transient spectroscopy (DLTS). In the DLTS spectra, a level ∼0.41 eV below the conduction band is attributed to V2 in accordance with previous assignments made by other authors. It is shown that the generation rate of V2 is not only determined by the primary electron energy, but also depends on the bombardment dose. Initially, the divacancy concentration depends linearly on dose while at high doses a gradual decrease in the generation rate occurs. The concentration of V2 increases significantly with depth close to the surface (≤3 μm) while for larger depths a constant value is reached. The experimental depth profiles are qualitatively compared with a theoretical curve. This curve is calculated assuming vacancy diffusion, and it is speculated that a substantial amount of the divacancies are formed by vacancy‐vacancy pairing. Furthermore, in some samples the depth profile of a level ∼0.23 eV below the conduction band is also monitored and based on these results the level scheme for V2 is discussed.