Characterisation of Dry Etching Damage in III-V and II-VI Semiconductors

[摘要] Dry etching induced surface damage has been characterised, in a novel way, for thin n+ GaAs epitaxial layers, by measuring the surface conductance using the Transmission Line Model (TLM) technique and Hall measurements. Various dry etching processes have been investigated for example, rf Reactive Ion Etching (rf-RIE) using CH4/H2 and SiCl4, Electron Cyclotron Resonance (ECR-RIE) using CCl2F2/He and Ion Beam etching using Ar and Ne. The results of which have been compared with wet etching and damage depths have been obtained. Damage saturation effect, predicted by the theory, has been observed for the RIE GaAs. The modification in the depletion layer thickness induced by dry etching has been determined using Raman scattering of coupled LO phonon- plasmon modes on the TLM samples. Criteria for damage free etching are suggested Modifications induced by the dry etching to the surface chemistry of GaAs have been investigated using X-ray Photoelectron Spectroscopy (XPS). Information about the top 3nm of surfaces etched using CH4/H2 and SiCl4 has been obtained and compared with unetched samples. Damage to the sidewalls of nanostructures has been examined using Transmission Electron Microscopy using a dark field imaging technique and by High Resolution TEM. Quantum wire-like structures with widths down to 50nm have been etched using CH4/H2 and SiCl4 and have been used as TEM specimens. Changes in the stoichiometry of GaAs and disorder in the lattice have been observed. Wires made of etched-regrown material were examined and the quality of the growth interface was evaluated. A high resolution etch process was developed using ECR-RIE in CCl2F2/He. This process produced low damage in nanostructures. The damage has been characterised using TLM, n+ GaAs quantum wires, Raman scattering using LO coupled Phonon-Plasmon modes and LO phonon Raman scattering using undoped GaAs. A novel high resolution reactive ion etching process has been developed for a variety of binary and ternary II-VI semiconductor compounds using CH4/H2. The process is optimised to produce nanostructures in ZnTe, ZnSe, ZnSSe, ZnS, CdTe, CdMnTe and CdS. Dots 200nm high and 26nm in diameter have been demonstrated in ZnSe. The advantage of this process lies in the fact that exactly the same etching conditions are suitable for all II-VI Semiconductors, so that quantum wells of any variety can be easily etched. Finally, the modifications induced by the RIE in II-VI semiconductors are investigated by XPS, Photoluminescence and Raman scattering in ZnTe and ZnSe and by XPS and Schottky diode parameter evaluation in CdTe.

[发布机构] University:University of Glasgow

[关键词] Electrical engineering, Condensed matter physics