Chapter 4: Impurities And Dopants Flashcards
What is the difference between a dopant and an impurity?
A dopant is added on purpose, and an impurity is not
When is a dopant called a substituent?
For higher concentrations
What is an isovalent(heterovalent) substituent?
An atom with the same oxidation state than the host
What is an aliovalent substituent?
An atom with higher or lower oxidation state than the host
What are the two different types of cases for concentrations of impurities and dopants?
- Not equillibrium, solute is frozen in
- In equilibrium, solute is mobile
What are the reason for a solute to be frozen in?
The temperature is too low for the solute to be mobile in the crystal
How does the solubility limit (s.l.) affect the stability of a crystal NOT in equilibrium? (slide 5)
- Concentration of solute is below s.l., no 2nd phase present ⇒ system is stable
- Concentration of solute is below s.l., 2nd solute-rich phase present ⇒ system is metastable
- Concentration of solute above s.l. ⇒ system is metastable
What conditions is needed for the solute in a crystal to be mobile?
A high temperature is needed
How does the solubility limit (s.l.) affect the stability of a crystal in equilibrium? (slide 6)
- Total amount of solute is below s.l. ⇒ concentration of solute is constant
- Total amount of solute is above s.l. ⇒ concentration of solute is variable =0
What sort of doping would a lower-valent cation give?
Acceptor
What sort of doping would a higher-valent cation give?
Donor
What type of compensating defects would appear when doping with a donor?
There woulf be an excess of positive charges in the crystal ⇒ electrons and metal vacancies
What type of compensating defects would appear when doping with an acceptor?
There would be an excess of negative charges in the crystal ⇒ holes and oxygen vacancies
