\documentclass[tikz,border=8pt]{standalone}
\usepackage{pgfplots}
\usepgfplotslibrary{groupplots}
\pgfplotsset{compat=1.18}
\begin{document}
\begin{tikzpicture}
\begin{groupplot}[
  group style={group size=2 by 1,horizontal sep=1.65cm},
  width=7.1cm,height=7.1cm,
  axis lines=middle,clip=false
]
\nextgroupplot[
  title={n-channel JFET saturation transfer},
  xmin=-1.08,xmax=0.08,ymin=0,ymax=1.12,
  xlabel={$V_{GS}/|V_P|$},ylabel={$I_D/I_{DSS}$},
  xtick={-1,-0.5,0},xticklabels={$V_P/|V_P|$,$-1/2$,$0$},ytick={0,0.25,1}
]
\addplot[very thick,teal!75!black,domain=-1:0,samples=180]{(1+x)^2};
\draw[densely dashed] (axis cs:-1,0)--(axis cs:-1,1.03);
\nextgroupplot[
  title={ideal enhancement nMOS saturation transfer},
  xmin=-0.08,xmax=3.12,ymin=0,ymax=2.18,
  xlabel={$V_{GS}/V_{\rm th}$},ylabel={$I_D/(K V_{\rm th}^{2})$},
  xtick={0,1,2,3},xticklabels={$0$,$1$,$2$,$3$},ytick={0,0.5,1,2}
]
\addplot[very thick,blue!75!black,domain=0:1,samples=2]{0};
\addplot[very thick,blue!75!black,domain=1:3,samples=180]{0.5*(x-1)^2};
\draw[densely dashed] (axis cs:1,0)--(axis cs:1,2.03);
\end{groupplot}
\end{tikzpicture}
\end{document}
