Compound semiconductors
Why does Mg-doped GaN grown by MOCVD remain highly resistive rather than p-type right after growth, and what is the countermeasure?
- AMg evaporates away, so more Mg is added
- BHydrogen bonds with Mg and passivates the acceptors, so they are activated by annealing in nitrogen or electron-beam irradiation
- CGaN is an insulator, so p-type doping is impossible
Show answer and explanation
Answer: B. Hydrogen bonds with Mg and passivates the acceptors, so they are activated by annealing in nitrogen or electron-beam irradiation
Hydrogen from the MOCVD source gases bonds with Mg to form Mg-H complexes that do not act as acceptors. Hiroshi Amano and colleagues found that electron-beam irradiation, and later Shuji Nakamura and colleagues that annealing in nitrogen, drives out the hydrogen and makes the GaN p-type, leading to the blue LED.
- A. Mg does not disappear; it is passivated by bonding with hydrogen.
- B. Correct. Driving out hydrogen activates the Mg.
- C. GaN can be made p-type with suitable treatment.