RTP-Assisted Ex-Situ Analysis of (Ag,Cu)(In,Ga)Se2 Formation using Selenization

The addition of Ag to Cu-Ga-In precursors for reaction to form (AgCu)(InGa)Se₂ (ACIGS) has shown benefits including improved adhesion, greater process tolerance and potential for improved device performance. In this study, metal precursors were sputtered with Ag/(Ag+Cu) ≈ 0.25, 0.75, 1.00 and Ga/(Ga+In) ≈ 0.25. Chemical pathways of formation of the ACIGS were studied by rapid thermal processing assisted ex-situ time-progressive experiments at 450 °C under 5% Ar/H2Se atmosphere. The reaction time was varied from 2-45 min. Composition and structure were characterized by energy dispersive x-ray spectroscopy (EDS), x-ray fluorescence (XRF), x-ray diffraction (XRD) and Raman spectroscopy. Reaction pathways analysis for low Ag/(Ag+Cu) ≈ 25% indicate that multiple stable intermetallic phases were formed during the reaction including κ-(Cu,Ga)₂(Ag,In), ζ-(Ag,Cu)₃(In,Ga) and Cu₉(In,Ga)₄; and the reaction to form ACIGS was complete after 10 min. However XRD analysis showed that Ag tends to stay in the stable ζ-(Ag,Cu)₃(In,Ga) phase during the reaction at higher Ag/(Ag+Cu) ≈ 75% and 100% and this causes the longer reaction time and the non-uniformity. With Ag ratio =100%, the reaction was completed with formation of Ag(In,Ga)Se₂ and AgIn₅Se₈ within 20 min.