\begin{axis}[ xlabel=$T$ in \si{\celsius}
            , ylabel=$\nicefrac{g_{\mathrm{m}}}{I_{\mathrm{D}}}|_{\mathrm{max}}$ in \si{\per\volt}
            , xmin=-40
            , xmax=140
            , ymin=15
            , ymax=50
            , grid=both
            , width=9cm
            ]

  \tikzstyle{plotprop} = [ mark=none
                         , domain=-40:140
                         , samples=20
                         , smooth
                         , thick
                         ]
  \tikzstyle{annonode} = [ fill=white
                         , inner sep=1pt
                         ]

  \def \echarge {1.602e-19}
  \def \kboltz {1.38064852e-23}
  \def \tkelvin {273.15}

  \addplot[plotprop] {\echarge/(\kboltz*1.0*(\tkelvin+\x))};
  \node[ annonode
       , anchor =south west
       , rotate=-26
       ] at (axis cs:-20,30.6) {$n=1.0$};

  \addplot[plotprop] {\echarge/(\kboltz*1.1*(\tkelvin+\x))};
  \node[ annonode
       , anchor =south west
       , rotate=-28
       ] at (axis cs:-20,32.8) {$n=1.1$};

  \addplot[plotprop] {\echarge/(\kboltz*1.2*(\tkelvin+\x))};
  \node[ annonode
       , anchor =south west
       , rotate=-30
       ] at (axis cs:-20,35.4) {$n=1.2$};

  \addplot[plotprop] {\echarge/(\kboltz*1.3*(\tkelvin+\x))};
  \node[ annonode
       , anchor =south west
       , rotate=-32
       ] at (axis cs:-20,38.5) {$n=1.3$};

  \addplot[plotprop] {\echarge/(\kboltz*1.4*(\tkelvin+\x))};
  \node[ annonode
       , anchor =south west
       , rotate=-33
       ] at (axis cs:-20,42) {$n=1.4$};

  \addplot[plotprop] {\echarge/(\kboltz*1.5*(\tkelvin+\x))}; 
  \node[ annonode
       , anchor =south west
       , rotate=-35
       ] at (axis cs:-20,46) {$n=1.5$};
\end{axis}