The problems associated with the use of ion implantation during the preparation of compound semiconductors have been examined. In particular, the use of an encapsulant as protection during annealing was considered and the properties and ease of preparation of the ideal encapsulant were studied. Among the experimental techniques used to study the surface of thin film coatings on the semiconductors materials, reflection high energy electron diffraction (RHEED) was extremely useful in allowing the study of thin layers. Other techniques used in the work included scanning electron microscopy (SEM), Rutherford backscattering (RBS), rapid thermal annealing using a graphite strip heater and thin film deposition by evaporation and sputtering. Among the encapsulants studied were aluminium nitride and the zirconium nitride the former being the most important. A study was also made of the chemical reactivity of aluminium nitride to oxidation and hydration. It was found that AlN was resistant to oxidation in air up to about 1000°C and in an inert atmosphere up to at least 1400°C. It was shown that aluminium nitride reacts readily with water to form AlOOH. The reproducibility of a good quality evaporated AlN film as an encapusulant was found to be difficult to control, but a combination of AlN and Si[3]N[4] in a "sandwich" proved to be more successful. Zirconium nitride was found to be useful as a passivation layer up to 700°C. Sputtered AlN coatings seemed to offer the best hope of success but further work is needed to improve the sputtering techniques so that free Al, or Al[2]O[3] is not present in the AlN layers.