Surface diffusion is shown to be the important factor in sputter–induced ripple and cone development on GaAs and InP surfaces for conditions typical of depth profiling when using surface analysis techniques. Ripple formation has been observed on both GaAs and InP when sputtered using Cs+ and O+2 ion beams. For GaAs, the ripple ‘‘wavelength’’ increases with sample temperature in the range from 45 to 100 °C, in qualitative agreement with the surface diffusion model of Bradley and Harper. No ripple formation is observed when the GaAs sample is cooled to −30 °C where surface diffusion is limited, or heated above 100 °C, where a proposed surface phase change may alter the diffusion rate. Ripple development also occurs on InP, but it is impossible to observe at 100 °C due to extensive cone formation. At this elevated temperature, Ar+ sputtering of InP leads to a surface enrichment of indium that is accompanied by a change in the In M4,5N4,5N4,5 Auger line shape toward that for indium metal. This result, together with the observation that cone formation is eliminated for sputtering at −20 °C, supports the intrinsic model where sputtering causes indium enrichment and surface diffusion that results in the agglomeration of indium metal into clusters. These clusters produce cone formation, possibly through the difference in sputter rates of indium and InP.
The effects of background doping, surface encapsulation, and As4 overpressure on carbon diffusion have been studied by annealing samples with 1000 Å p-type carbon doping spikes grown within 1 μm layers of undoped (n−), Se-doped (n+), and Mg-doped (p+) GaAs. The layers were grown by low-pressure metalorganic chemical vapor deposition using CCl4 as the carbon doping source. Two different As4 overpressure conditions were investigated: (1) the equilibrium pAs4 over GaAs (no excess As), and (2) pAs4 ∼2.5 atm. For each As4 overpressure condition, both capless and Si3N4-capped samples of the n−-, n+-, and p+-GaAs crystals were annealed simultaneously (825 °C, 24 h). Secondary-ion mass spectroscopy was used to measure the atomic carbon depth profiles. The carbon diffusion coefficient is always low, but depends on the background doping, being highest in Mg-doped (p+) GaAs and lowest in Se-doped (n+) GaAs. The influence of surface encapsulation (Si3N4) and pAs4 on carbon diffusion is minimal.
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