Transistors.
A transistor is made up of three elements the Base, the Collector and the Emitter. There are two types of Transistors NPN and PNP type. The difference being that the NPN has one P layer sandwiched between 2 N layers and the PNP has one N layer sandwiched between two P layers.
(key b) Base, c) Collector e) emitter)
The important difference is pretty obvious the PNP works in oposite to the NPN transistor, an example of this can be found in a A/B type Amplifier.
Crystals.
The crystal mateial that goes into making transistors is mostly (although not always) Silicon or Germanium an element that has four in its external shell. Which allows chemical bonds with upto 4 connections. Dependent on the Doping of the crystal you can end up with either an N type or a P type Transistor latice.
N type Materials
A small amount of an element with 5 outer electrons (ie Phosperous, Antimony or Arsenic)
P type Materials
With P type elements they have 3 outer electrons (Indium, Aluminium and Boron) leaving vacant bonds on the crystal.
Making the Transistor
As you will be aware for each type you will need that appropriate number of latices, ie for a PNP you will need 2 P latices and 1 N latice.