Hi Abdulkadir,
This documentation link is a good place to start for Diode modeling in Simulink: http://in.mathworks.com/help/physmod/elec/ref/diode.html
It has the following representations:
- Piecewise Linear
- Piecewise Linear Zener
- Exponential
Each of these representation has parameters that can be changed to according to your custom model. Those include sections like Reverse breakdown, Ohmic resistance, Capacitance, Temperature dependence etc.
Abel