Some of your notes in Volume 3 (Semiconductors) are incomplete. Some of the slides have four bullets, there of them empty and one of them that says Review.

 

On the opening page of the All About Circuits website, the following is written:

This site provides a series of online textbooks covering electricity and electronics. The information provided is great for both students and hobbyists who are looking to expand their knowledge in this field. Please keep in mind that the textbooks are not 100% complete. They are a continuous piece of work, and thus will continually be updated.

Such sections will be completed in the future.