The present invention relates in general to a process for depositing epitaxial films of Group III-V semiconductor substrate crystallographically compatible therewith. In a more particular aspect, this invention relates to a process for depositing an epitaxial film of a ternary III-V compound by a vapor phase epitaxy-hydride technique using a binary III-V alloy, as the metallic source. The resulting epitaxial structures find particular utility in the fabrication of light emitting diodes, field effect transistors, and double heterostructure lasers.
Epitaxial films composed of semiconductor compounds containing elements from group III and group V of the Periodic Table of Elements are major components in the fabrication of optoelectronic and microwave devices. These devices provide the foundation for future advances in the area of optical communication and radar technology. Consequently a considerable research effort has evolved in an attempt to provide more useful and efficient III-V compounds of high quality. The need for high quality semiconductor structures is most important in the area of optical communications and radar technology. These devices form an integral part of present day tactical weapons systems. Laser and photodetectors are examples of devices used in optical communication systems, and III-V semiconductor-substrates are the basic structures used in the fabrication of such devices. The use of high quality III-V semiconductors of good morphology with defect-free surfaces contributes significantly to an overall improvement in the efficient operation and extended lifetime of lasers and photodetectors, thus increasing the efficiency and reliability of tactical communication and weapon systems.
The III-V epitaxial structures and semiconductor applications, such as those employed in the fabrication of optical communication and radar systems generally include the arsenides, antimonides, phosphides and nitrides of aluminum, boron, gallium or indium, as well as ternary and quaternary mixtures thereof. These compounds in general, are deposited as crystalline films on semiconductor substrates by either vapor phase or liquid phase epitaxial techniques.
In vapor phase epitaxy, a number of specific processes are known for effecting the deposition of III-V films. These processes usually include the steps of reacting two gaseous mixtures within an enclosed reaction chamber to provide a III-V compound. The two gaseous mixtures generally utilized in vapor phase epitaxy comprise as one of them, a first gaseous mixture formed by contacting a Group III element with hydrogen halide; while the other, or second gaseous mixture, is formed by mixing hydrogen, as a carrier gas, with a Group V element in gaseous form. The III-V compound resulting from the interraction of the two gaseous mixtures is then deposited as an epitaxial film onto a suitable semiconductor substrate. The semiconductor substrate may be similar or different than the material used to form the epitaxial films and generally include III-V compounds, II-VI compounds, as well as silicon and germanium.
One of the better known methods for producing III-V compounds is referred to as the vapor phase epitaxial-hydride technique (VPE-Hydride). The specific details of this technique are set forth in a review paper by G. H. Olsen and T. J. Zamerowski, "Crystal Growth and Properties of Binary, Ternary and Quaternary (In, Ga) (As,P) Alloys grown by the Hydride Vapor Phase Epitaxy Technique", B. R. Pamplin (ed): Progress in Crystal Growth and Characterization, Vol. II, Pergamon Press Ltd., London (1981), pp 309-375.
Unfortunately, the growth of III-V ternary compounds, especially the preparation of the InGaAs, InGaP and InGaSb ternary alloys is difficult and the resulting crystalline films lack good morphological characteristics and often possess a high number of impurities. The defects produced during the growth of epitaxial films of the above type originate from a number of sources, e.g., dislocation on the substrate, inappropriate epitaxial growth conditions, and the presence of foreign matter or impurities during the growth process. Since these particular compounds are of great importance in the fabrication of double heterostructure lasers, photodetectors, light-emitting diodes and other optical communication devices, a considerable research effort was undertaken in an attempt to provide novel methods for preparing ternary III-V compounds as epitaxial films which possess good morphological characteristics.