P-N diode charge density, space charge field, potential, I-V curve

From Optical Imaging and Spectroscopy (Wiley - OSA 2009)
By David J. Brady
www.opticalimaging.org
Figures 5.4 and 5.5

nd=1;
na=0.7`;
rho[x_]:=(1/2) na (Sign[x]-1) (E^(na x))+(1/2) nd (Sign[x]+1) (E^(-nd x));
Ef[x_]:=(1/2) (Sign[x]-1) (E^(na x))-(1/2) (Sign[x]+1) (E^(-nd x));
V[x_]:=-(((Sign[x]-1) (E^(na x)))/(2 na))+((1/(2 na))+((1-(E^(-nd x)))/(2 nd))) (Sign[x]+1);
Plot[rho[x],{x,-6,6},Axes->False]
Plot[Ef[x],{x,-6,6},Axes->False]
Plot[V[x],{x,-6,6},Axes->False]

<<"PhysicalConstants`";
isat=1;
VT=((Coulomb (290 Kelvin) BoltzmannConstant)/(Joule ElectronCharge));
current[V_]:=isat ((E^(V/VT))-1);

Plot[current[V],{V,-2 VT,2 VT},Axes->False,Frame->True,FrameLabel->{"V (volt)","I (\!\(\*SubscriptBox[\(i\), \(sat\)]\))"}]