Gallium incorporation kinetics during gas source molecular beam epitaxy growth of GaN

Abstract

The kinetics of gallium incorporation during gas source molecular beam epitaxy (GSMBE) growth of GaN are investigated for varying substrate temperature ( T s) and incident ammonia flux ( J NH 3 ). Incident Ga atoms eventually either (1) react with NH 3 to form GaN, (2) accumulate on the film surface, or (3) desorb. For an incident Ga flux ( J Ga) of 0.30 monolayer/s and an incident flux ratio of J NH3 J Ga ∼ 10 3 , desorption of Ga is significant for T s above ∼ 700°C, and Ga surface accumulation is significant for T s below ∼ 750°C. Two distinct activation energies for Ga desorption are observed: 1.4 ± 0.1 eV for 625°C < T s < 740°C and 0.4 ± 0.1 eV for 740°C < T s < 825°C. The rates of Ga desorption and Ga surface accumulation are both suppressed by increasing J NH3. These effects combine to produce a GaN formation rate which increases with increasing J NH3 and which peaks at T s ∼ 750°C over the range of J NH3 investigated. These results are consistent with a model based on the T s-dependent reactivity of NH 3 towards Ga and indicate the presence of a relatively complex surface chemistry, with a strong likelihood that hydrogen is playing an important role.