How are dopants chosen for producing semiconductor devices? I've heard that boron and phosphorus are some common dopant elements, but you'd want different ones for different semiconductors, right? They need to be compatible with the crystal structure. Could you dope a compound semiconductor by altering the ratio of its component elements?
Is there any advantage to using different dopants, in different devices or within the same device? What if, for example, you made a silicon BJT where the collector was doped with nitrogen, the base doped with boron, and the emitter doped with phosphorus? Would that have significantly different properties to a device using phosphorus on both the emitter and collector?
Best Answer
Boron (acceptor) and Phosphorus/Arsenic (donor) are common the dopants used for Silicon devices. Different dopants has to be used used for another semiconductor. I don't know if doping can be done by changing the composition in compound semiconductors. But other atoms can be used to dope compound semiconductors also. For example, Zinc (acceptor), Sulphur (donor) and Silicon (amphoteric) can be used for Gallium Arsenide.
Other than the process compatibility and cost effectiveness, few conditions that a dopant should satisfy are
Dopants will introduce an energy level (acceptor or donor type) in the forbidden gap of the semiconductor. These energy levels should be closer to the band edges (valance or conduction band) so that the dopants are active at room temperature.
The dopant should have good solubility in the semiconductor. More the solubility, more the doping concentration that can be achieved.
I don't know if there are any advantages of using multiple dopants. It's defenitely increases the cost as multiple dopants demands additional tools or extra fabrication steps.
Since nitrogen is a gas, it is not a a good idea to use it as a dopant. But if we take an arsenic doped and phosphorus doped region, the electrical properties will be same for practical range of temperatures and dopings.