Electron Traps in GaAs Grown by Molecular Beam Epitaxy on On-axis (100) and Off-axis Substrates

Deep level transient spectroscopy (DLTS) was used to characterize the electron traps present in the bulk GaAs grown by molecular beam epitaxy (MBE) on on-axis (100) and off-axis (4° towards the (111) A direction) substrates. Two electron traps were obtained for each sample having identical corresponding peak locations in the DLTS spectra. The layer grown on the on-axis substrate has electron traps with activation energies of E C –0.454 eV and E C –0.643 eV and capture cross-sections of 1.205 x 10 -14 cm 2 and 3.88 x 10 -15 cm 2 , respectively. The layer grown on the off-axis substrate has traps with activation energies of E C –0.454 eV and E C –0.723 eV and capture cross-sections of 2.060 x 10 -14 cm 2 and 4.40 x 10 -14 cm 2 . The electron traps are possibly the M4 (or EL3) and EL2 (or EB4) traps commonly found in GaAs layers. Due to the high trap concentrations obtained and to the non-uniform trap concentration profile, As desorption may be considerable during growth.