DOPANT EVAPORATION SOURCES FOR MOLECULAR-BEAM EPITAXY

Two simple dopant evaporation sources are described and characterized for use in a III-V molecular beam epitaxy (MBE) system. The first is f or the evaporation of silicon donors and utilizes a strip of silicon f rom a commercial doped wafer. The advantages are its cleanliness as sh own by the significantly lower compensation ratio, speed of response t o current changes allowing abrupt doping changes, efficiency and relia bility. Following the design considerations of the silicon strip sourc e we constructed a beryllium source. Instabilities in the heating patt ern showed that beryllium could not be reliably used until we redesign ed the source to allow the beryllium to be held by a tantalum foil. Th is redesign was successful, with high efficiency and fast response, bu t secondary ion mass spectrometry (SIMS) results show oxygen incorpora tion similar to that of conventionally evaporated beryllium. The same SIMS results show abrupt ( less-than-or-equal-to 50 angstrom) doping p rofiles made by changing the current through the source (i.e. without the use of the shutter).