2 - Epitaxial Growth of II–VI Compounds by MOVPE

Abstract

This chapter reviews the present state of metal organic vapor phase epitaxy (MOVPE) of wide gap II–VI semiconductors—a class of materials—which is typically represented by ZnSe and related ternary and quaternary compounds. Epitaxial growth of large gap II–-VI compounds has attracted a renewed interest, since the successful operation of blue diodes and injection lasers based on ZnSe related material. Although MOVPE of II–VI compounds has not yet reached the same maturity as MBE growth, important progress has been made in the past years. MOVPE needs specially designed molecules. Their architecture and their weak and strong bonds play an important role in the solid/gas­-phase reactions in which, in some cases, even the carrier gas is involved. Because MOVPE works at a finite pressure, the molecules have the chance to undergo many collisions; volatile products—especially hydrocarbons—are quickly released from the solid surface into the gas phase. However, in MO-MBE, the precursor molecule is—in most cases—at first destroyed in the cracker cell. Then the fragments, which contain C, CH, C2, and HE, reach the solid surface. Those parts, which do not quickly leave by desorption have a good chance to be incorporated, and lead to unacceptable large carbon and hydrogen incorporation. Therefore, in most applications of MO-MBE, those advantages of MOVPE connected with solid/gas reactions and with the architecture of the molecules are lost, and only the easy flow control of volatile elements remains.