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

Two microscopic analytical techniques, extended X-ray absorption fine structure (EXAFS) and perturbed angular correlation (PAC), have been utilised to characterise ion-induced amorphisation in compound semiconductors at the atomic scale. The structural parameters of stoichiometric, amorphised GaAs were determined from EXAFS measurements. Relative to a crystalline sample, the 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 atoms from the crystalline value of 4. All measured parameters were independent of implant conditions and were thus considered indicative of the intrinsic, amorphous phase as opposed to an extrinsic, implantation-induced structure. Furthermore, the heterogeneous amorphisation of InP was quantified with PAC measurements. Dose-dependent crystalline, disordered and amorphous environments of the In-111 probes were established and a direct amorphisation process was identified. (C) 1999 Elsevier Science B.V. All rights reserved.