\documentclass{standalone}

\usepackage{tikz}

\begin{document}
\begin{tikzpicture}

\draw(-3,0)--(3,0);
\draw(0,-1.5)--(0,3);

\draw[line width=1.5pt](-2.5,0)--(0,0)--(0,2.5)--(1.975,-1.25);
\draw(1.5,1.5)node{\small$U-Ex$};

\draw[line width=1pt, densely dotted](-2.5,1)--(0,1);
\draw(-2.8,1)node{\small$E_F$};

\draw(0,3.3)node{\small$V$};
\draw(3.3,0)node{\small$x$};

\end{tikzpicture}
\end{document}

