Atomic-level characterisation of ion-induced amorphisation in compound semiconductors

Two microscopic analytical techniques, extended X-ray absorption fine struc ture (EXAFS) and perturbed angular correlation (PAC), have been utilised to characterise ion-induced amorphisation in compound semiconductors at the a tomic scale. The structural parameters of stoichiometric, amorphised GaAs w ere determined from EXAFS measurements. Relative to a crystalline sample, t he nearest-neighbor bond length and Debye-Waller factor both increased for amorphous material. In contrast, the coordination numbers about both Ga and As constituent atoms in the amorphous phase decreased to similar to 3.85 a toms from the crystalline value of 4. All measured parameters were independ ent of implant conditions and were thus considered indicative of the intrin sic, amorphous phase as opposed to an extrinsic, implantation-induced struc ture. Furthermore, the heterogeneous amorphisation of InP was quantified wi th PAC measurements. Dose-dependent crystalline, disordered and amorphous e nvironments of the In-111 probes were established and a direct amorphisatio n process was identified. (C) 1999 Elsevier Science B.V. All rights reserve d.