Molecular beam epitaxy (MBE) is a crystal growth technique capable of growing ultrathin layered heterostructures for basic studies, and devices such as modulation doped field‐effect transistors (MODFET’s), heterojunction lasers, heterojunction bipolar transistors (HBT’s), and superlattices. By using a dimeric arsenic source to grow GaAs and AlGaAs layers, the crystalline quality of these devices and structures may be improved, ultimately improving device performance. The design of a novel large capacity effusion cell (capable of producing about 700 &mgr;m GaAs growth) for cracking tetrameric arsenic into dimeric arsenic and the results of its use are described.