COPPER-INDUCED DEEP LEVEL DEFECTS IN GAAS[0.6]P[0.4] ALLOY SEMICONDUCTOR

Abstract

The main objective of the present study is to characterise copper-induced deep level defects in n-type GaAso.6P0.4 by Deep Level Transient Spectroscopy (DLTS) technique. In order to have a controlled study, three types of aluminium/GaAso. 6Pa. 4 Schottky diodes were fabricated. The first diode was unannealed, the second diode was thermally annealed at 480°C and the third diode was copperdiffused at 480°C. Detailed diode characterisations were performed on these samples. In addition, the effective Richardson constant A* for the thermally annealed sample was determined to be 7 A/cm2K2 . In comparison, the Schottky diode quality was found to have improved after 480°C thermal treatment. It was probably due to a reduction in the surface oxide as a result of the thermal treatment. We also demonstrated that the fabricated Schottky diodes were suitable for use in the DLTS study. Copper was successfully diffused into the n-type GaAs0.6P0.4 at 480°C. C-V analysis on this copper-diffused sample showed that there is a strong frequency-dependence of the junction capacitance, and this indicates the presence of deep traps. Transient capacitance measurement were performed on the samples. The results showed that there was no measurable epitaxial-related defect in the GaAso. 6Po. 4 wafer and the thermal treatment at 480°C did not introduce any significant deep level defect in the bulk of the semiconductor. On the other hand, two electron traps were detected in the copper-diffused sample. Trap A occured at a location further away from the junction edge as compared to Trap B. The activation energies of the traps determined by DLTS technique were found to be 0.13eV and 0.07eV for Trap A and Trap B respectively. The capture cross sections were also determined to be 1.2 x 10-22 and 3.3 x 10-23 cm2 for Trap A and Trap B respectively. Trap A has a faster carrier emission and capture rates as compared to Trap B. Based on the very small carriers capture cross section of both traps, it is believed that both copper-induced electron traps in our system were associated with repulsive centres which can give rise to rapid non-radiative carriers capture process. Trap A which occurred in the bulk of the semiconductor has been conjectured to be related to CuGa defect. On the other hand, Trap B is probably due to Cui+ positive ions which have reacted with the lattice vacancies to form copper complexes near the surface of the sample. Both traps are unlikely to be donor-related defects.