4 - Metal Organic Chemical Vapor Deposition: Technology and Equipment

Abstract

Metal-organic chemical vapor deposition (MOCVD) has assumed a great deal of technological importance in the fabrication of a number of opto-electronic and high speed electronic devices. Much of the appeal of MOCVD lies in the fact that readily transportable, high purity organometallic compounds can be made for most of the elements that are of interest in the epitaxial deposition of doped and undoped compound semiconductors. A large driving force (i.e., a large free energy change) exists for the pyrolysis of the source chemicals,which ensures that a wide variety of materials can be grown using this technique that are difficult to grow by other epitaxial techniques. The growth of Al-bearing alloys and P-bearing compounds are especially noteworthy. In fact, the growth of P-containing materials using molecular beam epitaxy (MBE) technology has been addressed by using P sources and source configurations that are similar to those used in MOCVD in an MBE-like growth chamber. The versatility of MOCVD has resulted in it becoming the epitaxial growth technique of choice for commercially useful light emitting devices in the 540 nm to 1600 nm range and, to a somewhat lesser extent, detectors in the 950 nm to 1600 nm range. These are devices that use GaAs or InP substrates, require thin, doped epitaxial alloy layers that consist of various combinations of In, Ga, Al, As, and P, and which are sold in quantities significantly larger than laboratory scale. The most basic growth parameters that are varied in MOCVD are the growth (susceptor) temperature and the input reactant molar flows.