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The design of a tantalum nozzle for group V hydride cells in gas source molecular beam epitaxy is presented. The nozzle, which determines the flux distribution from the group V cell is optimized for uniformity and maximum flux utilization. Arsine cracking efficiency and relative concentrations of various gas species are measured by a quadrupole mass analyzer. The operating temperature for the source cell is determined as the region where maximum dimeric arsenic is available for growth.

A variety of optical methods is now available for studying surface processes and for monitoring layer thicknesses and compositions during semiconductor crystal growth by molecular beam epitaxy, organometallic chemical vapor deposition, and related techniques. New capabilities for surface analysis are provided by new techniques such as reflectance‐difference spectroscopy, which use intrinsic symmetries to suppress ordinarily dominant bulk contributions. Bulk and microstructural properties such as compositions and layer thicknesses can be determined directly by techniques such as spectroellipsometry, which return information integrated over the penetration depth of light. Proven capabilities suggest new applications to interrupted growth and to metastable materials systems involving self‐ordering and strain relaxation. The first closed‐loop system for controlling semiconductor crystal growth, which uses a spectroellipsometer as the monitoring element, is briefly described.

Using closed‐loop ellipsometric feedback control, we have grown a variety of epitaxial AlxGa1−xAs structures by chemical beam epitaxy where compositions x vary continuously with thickness according to a given input function. Present limits are exemplified by a 200 A parabolic quantum well structure grown using compositions determined from the outermost running ∼3 A (∼1 monolayer) of depositing material.