An Analysis of the Derivative Weight-Gain Signal From Measured Crystal Shape: Implications of Diamater Control of GaAs

GaAs is one of the key semiconductor materials that serves as a substrate for light-emitting diodes (LEDs), lasers, and field-effect transistors (FETs). Paralleling the development pattern of growth techniques for other single crystals, the issues of primary interest have 477 LEC technique. 478 evolved from questions of quality (elimination of twinning and defects, doping uniformity) to that of economy of size. However, scaling up the dimensions of GaAs crystals grown by the liquid-encapsulated Czochralski (LEC) technique necessitates introducing sophisticated schemes for diameter control. By achieving satisfactory control, it will also be possible to run for extended periods of time with minimal supervision, and to attain higher crystal yields, as well as a reduction in defect generation brought on by shape change. Since diameter control in Czochralski growth has been the subject of an excellent recent review by Hurle,1 here a brief outline of previous efforts with respect to LEC growth will suffice. Unlike Si2 and a wide variety of oxide crystals3 (e.g., GGG, LiTa0 3 ) for which successful diameter measurement and control systems have been developed, the realization of a viable system for the LEC growth of III-V compounds has been much more difficult to achieve. This is largely due to effects associated with the growth chamber under high pressure, the presence of the encapsulating layer of E^CM/), and the phenomenon of anomalous density (rfuquid > ckoiid) in some semiconductor materials.