    \begin{tikzpicture}
      \draw[fill=black,opacity=0.1] (1,-6) rectangle (4,1);
      \draw (0,0) -- (1,0) edge[out=0, in=180] (4,-2) (4,-2) -- (6,-2)
            (0,-3) -- (1,-3) edge[out=0, in=180] (4,-5) (4,-5) -- (6,-5);
            %(0,-2.5) edge[dashed] (6,-2.5);
      %\node[anchor=south east] at (6,-2.5) {$E_F$};
      \node[anchor=south east] at (6,-2) {$E_C$};
      \node[anchor=south east] at (6,-5) {$E_V$};
      \draw[dotted] (1,-6) -- (1,1) (4,-6)--(4,1);
      \node at (0.5,0.5) {\large P};
      \node at (2.5,0.5) {\large $\longleftarrow \mathcal{E}$};     
      \node at (2.5,-5.5) {\large $\longleftarrow \mathcal{E}$};     
      \node at (5.5,0.5) {\large N};
      \node[circle,inner sep=0,draw,blue] at (2,-3.75) (estart) {$-$};
      \draw[red,decorate,decoration={snake},-stealth,thick] (2,-2.25) node[circle,red] (photon) {$\nu$} (photon) -- (estart);
      \node[circle,draw,red,inner sep=0,thick] at ($(estart)+(0.6,3.2)$) (emobile) {$-$};
      \node[circle,draw,red,inner sep=0,thick] at ($(estart)+(0.6,-1)$) (hmobile) {$+$};
      \draw[blue,-stealth] (estart) edge[out=0,in=270,-stealth,thick,looseness=0.5] (emobile);
      \draw[blue,-stealth] (estart) edge[out=0,in=90,-stealth,thick,looseness=0.5] (hmobile);
      \draw[green!50!black,-stealth] (hmobile) edge[out=180,in=0,thick,-stealth] (0.5,-3.5);
      \draw[green!50!black,-stealth] (emobile) edge[out=0,in=180,thick,-stealth] (4.5,-1.5);
    \end{tikzpicture}
