Fig. 1. (Color online) Schematic of (a) isotropic etching and (b) anisotropic etching.

Fig. 2. (Color online) Schematic of one plasma ALE cycle generic concept.

Fig. 3. (Color online) (a) Measured data of etching rate per cycle for a fixed BCl₃ plasma time per cycle and varying oxygen plasma time per cycle. (b) The linear behavior of the plasma ALE etching rate versus the number of plasma ALE cycles^[64].

Fig. 4. (Color online) Schematic of mechanism of GaN O₂–BCl₃ plasma ALE.

Fig. 5. (Color online) Schematic of one Cl₂/BCl₃-inert gas plasma ALE cycle generic concept.

Fig. 6. EPC of GaN as a function of bias voltage^[52].

Fig. 7. (Color online) GaN plasma ALE process and initial parameters^[78].

Fig. 8. EPC as a function of the absolute value of the self-bias potentialV_DC by varying RF bias for (a) an removal by Ar plasma with an RF source set at 100 W (full triangle) and 120 W (empty triangle) and (b) an activation by Kr plasma for an RF source set at 100 W (full square) and 120 W (empty square)^[80].

Fig. 9. (Color online) (a) Post-etching GaN layer thickness for the unetched reference, after the chlorination step only, after He or Ar plasma only and after full He or Ar plasma ALE (60 cycles) and (b) energy scan for Ar and He ALE processes^[83].

Fig. 10. (Color online) The mechanism of Cl₂–He plasma ALE process.