LOW-ENERGY FOCUSED ION-BEAM DOPING DURING MOLECULAR-BEAM EPITAXIAL-GROWTH FOR THE FABRICATION OF 3-DIMENSIONAL DEVICES - THE EFFECT OF DOPANT SURFACE SEGREGATION

An extreme example of surface segregation is found in Sn-doped GaAs gr own by molecular beam epitaxy (MBE). Abrupt changes in the doping prof ile are not possible, instead the dopant concentration decreases expon entially towards the wafer surface from the point at which doping tvas terminated. In this work it is shown that segregation can be suppress ed by implanting the Sn from a very-low-energy (50 to 300 eV) ion beam during growth. The effect of ion implantation energy is studied using secondary ion mass spectroscopy (SIMS) to measure the depth profile o f the implanted Sn, It is found that the level of incorporation can be increased by up to a factor of eight using a 300 eV ion energy.