Electrical measurement of the lateral spread of the proton isolation layer in GaAs

Information on the lateral spread of ions and/or damage is contained in the depth distribution normal to a target surface if ions are implanted into a tilted target. Following this principle the lateral spread of the carrier removal distribution formed by 300-, 400-, and 500-keV proton implants in GaAs is evaluated from the several depth distributions of carrier removal which are formed by implants with different tilting angles and measured by the Copeland method. It is found that the lateral spread of carrier removal is largest at a depth near the projected range of protons. For instance the removal rate drops to 10% of its maximum value at about 0.7 μ laterally from a mask edge for 400-keV protons for which the projected range is about 3.3 μ. It is also found that the lateral spread increases as the incident energy increases but that the ratio of the lateral to the longitudinal spreads decreases