1. Formation of a PN Junction Diode and its Band Diagram:

http://www.acsu.buffalo.edu/~wie/applet/pnformation/pnformation.html

2. PN Junction Diode under Bias:

http://jas.eng.buffalo.edu/education/pn/BiasedPN

3. Fermi Level and Carrier Concentration Applet 
(Doping of Donor and Acceptor Impurities):

http://jas.eng.buffalo.edu/education/semicon/fermi/bandAndLevel/fermi.html

4. PN Junction Diode under Bias

http://jas.eng.buffalo.edu/education/pn/biasedPN2/BiasedPN2.html