The whole concept of crystal orientation becomes important during
- The etching of the crystal
This introduces an orientation dependency that influences the properties of GaAs field effect transistor. For example, during implantation, when a high energy ion enters a single crystal lattice at a critical angle to the major axis of the GaAs crystal, the ion is steered down the open directions of the lattice. This steering is called axial channelling. This implies that of a random equivalent direction is not used during ion implantation, the depth distribution will be greater than those predicted by range statistics which are used to establish penetration depth.
The channelling effect is not as dramatic in the <100> direction when compared with <110> direction. Many of the current GaAs wafers employ the <100> direction. It should be noted that the profile difference between the aligned <100> direction implant and any other direction of implant has a significant influence upon the threshold voltages of the fabricated devices.