Electrical characterisation of Cu-Diffusedn-GaAs epitaxial layers using optical deep level transient spectroscopy

Abstract

Undopedn ^--GaAs epitaxial layers were grown by OMVPE onn ⁺ (1 × 10¹⁸ cm³) and semi-insulating (SI) GaAs substrates. The as-grown epitaxial layers grown onn ⁺ substrates contained several deep level defects whereas those grown on SI substrates were, apart from the EL2, virtually “defect free”. Upon Cu diffusion, deep levels which may reduce hole and electron diffusion lengths and lifetimes, were formed. Optical deep level transient spectrocopy (ODLTS) has been used to identify such levels atE _v + 0,41 eV andE _c-0,31 eV respectively. The EO1 (EL2) trap concentration reduced after Cu had been diffused into the epitaxial layers. The magnitude of this reduction was approximately equal to the concentration of the trap found atE _c - 0,31 eV which suggests that the two may be related. Activation energies and capture cross-section values are presented for the deep levels detected in these epitaxial layers.