Proton Implantation Induced Damage to Heavily Doped n-GaAs as Envisaged by Charge Deep-Level Transient Spectroscopy

Abstract

Heavily doped (1 to 3 x 10 18 cm -3 ) GaAs:Si wafers were exposed to high doses (10 14 , 10 15 cm -2 ) of 150 keV protons. When applying the lower dose, the related charge DLTS spectra of Al/GaAs diodes comprise a peak of dielectric relaxation (DR) and a trap-limited peak (MG) due to the emission from a midgap level. The former peak can be attributed to a linear Debye-type polarization connected with a hopping transport of electrons within the damaged region. If taking samples from different positions on the original wafer, the position of the DR peak on the temperature axis T m , for a selected rate window has been found to vary when passing from one sample to another, a shift toward higher temperature has been accompanied by a corresponding increase in the activation energy (0.1 to 0.22 eV). The MG level emission rate is quite sensitive to the electric field intensity in the semiconductor, as manifested by shifting T m to lower temperatures via higher reverse biases. By contrast, the ultimate dose of 10 15 protons/cm 2 introduced defect levels at 0.07 and 0.31 eV below E c , respectively, a result that can be reconciled with previous reports relevant to lower doses. Concluding, the DR peak occurrence may be considered as a criterion for a successful GaAs isolation after the impact of protons, the optimum dose lying closely to the 10 14 cm -2 level.