We performed the nitridation of (001) GaAs surfaces using nitrogen molecules (N 2 ) cracked by a hot tungsten filament. After nitridation of a GaAs surface at 620°C for 90 min, the  RHEED pattern shows the mixed spotty pattern of GaAs and GaN, while the  RHEED pattern shows a streak pattern with the spacing of a GaAs lattice. The nitridation rate is independent of the substrate temperature below 530°C. Above 590°C, N 2 desorbs from the surface during nitridation. This desorption rate of N 2 from the nitrided GaAs surface is the smallest among those of column V molecules in InAs, InP, GaAs and GaP, due to the large standard heat of formation for GaN.
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