Admittance spectroscopy of solar cells based on GaPNAs layers

Admittance spectroscopy is used to study defect levels in the layers of a GaPNAs quaternary solid solution. Centers with an activation energy of 0.22 eV and a capture cross section of ∼2.4 × 10⁻¹⁵ cm² are found in doped n-GaPNAs layers grown on GaP substrates. These centers correspond to already known Si_Ga + V_P defects in n-GaP; annealing decreases their concentration by several times. A level with an activation energy of 0.23–0.24 eV and capture cross section of ∼9.0 × 10⁻²⁰ cm² is found in undoped GaPNAs layers grown on Si and GaP substrates. The concentration of these centers substantially decreases upon annealing, and, at annealing temperatures exceeding 600°C, there is absolutely no response from these defects. For undoped GaPNAs layers grown on GaP substrates, a level with an activation energy of 0.18 eV and capture cross section of ∼1.1 × 10⁻¹⁶ cm² is also found. The concentration of these centers remains unchanged upon annealing