You can run "poisson" on any Sun SPARCstation. type in these commands:
% add 6.012
% /mit/6.012/sss/poisson&
The upper graph's black line is proportional to charge density, Rho/q.
You can choose between two different devices: 1) p-n junction diode 2) MOS capacitor.
DEVICE: p-n junction
Choose between 'exact' or 'approximate' solutions. The 'approximate' solution is for the depletion approximation.
Choose the doping levels and watch how the depletion region changes as you make one side more heavily doped than the other.
Change the voltage bias (Vapplied) and watch the depletion region shrink and grow. As it goes into 'forward bias' it will shrink. As it goes into 'reverse bias' it will grow.
The 'forward bias' will not grow larger than V = 0.7 V.
Disregard the bottom graph.
DEVICE: MIS diode (MOS capacitor)
Choose the doping type of the semiconductor part. Change to p-type.
Choose the doping level (Ni)
Choose Preset "poissn05". This sets the doping to NA=1e17 cm-3.
Note that the y-axis scale will change as you enter into the accumulation or inversion regimes.
Change the voltage bias and watch the charge density change. Around V = -0.35 V is VFB. As it goes more negative you get accumulation. Around V = 1.2 V is VT. As you go more positive you can see a delta function of negative charge appear at x=0. This corresponds to the inversion layer.