Hi
Please follow thw foll link instructor.physics.lsa.umich.edu/adv-labs/Photoelectric_Effect/Photelectric_analysis_notes.pdf .
Fig 2. Curves 1 and 2 show Millikan's data taken from the tables of Fig 1, replotted on the same current scale. Also included is his scaled curve II for reference. The data points on all three curves have been connected with simple splines.
Read the full article about asymptotic line in the curve from yhe following link www.oufusion.org.uk/PhotoelectricEffect.htm .