In-Situ Synthesis and Magnetically Stabilized Kyropoulos Growth of Undoped Indium Phosphide
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IN7-SITU SYTH3&SIS AND I TICAT.yLL OF UEKDOPED IZDILM PHOSPHIDE
STABILIMM KYROPOULOR GROWTH
STEPHEN BACHOWSKI, BRIAN S. AHERN, & ROBERT M. HILTON, Rome Air Development Center, Hansom AFB, MA 01731; AND JOSEPH A. ADAMSKI, Parke Mathematical Laboratories, Carlisle, MA 01741
The Kyropoulos growth technique has been combined with in-situ synthesis to yield high purity undoped crystals of 300 to 700 gm charges of InP. Etched wafers show a uniform dislocation density across 70mm diameter in contrast with the "W" pattern created by LEC. Use of an axial magnetic field in Kyropoulos growth reduces the dislocation density by an order 4 of magnitude, to 1 x 10 cm-7. By combining Kyropoulos growth with in-situ synthesis of the indium phosphide, high mobility (4.6xi0 4 at 77 C) undoped single crystals have been obtained.
High purity low dislocation density indium phosphide is becoming an increasingly important substrate material for optoelectronic devices. High mobility indium phosphide can be obtained by in-situ synthesis. Low and uniform dislocation density wafers may be obtained by magnetic liquid encapsulate Kyropoulos growth. The vapor pressure of phosphorus (27.5 atm) at the melting point of InP(1070 C) (1] presents a major obstacle to obtaining stoichiometric charges. Several methods have been employed to obtain stoichiometric polycrystalline InP. The two best known synthesis routes are enclosing indium and phosphorus in a sealed ampoule within a horizontal pressure furnace and using a very high pressure autoclave systems [2,3]. These methods result in polycrystalline InP ingots which are then remelted for use in Czochralski growth. In-situ synthesis yields purer material but is complicated by the fact that phosphorus changes phase when it is heated. Red phosphorus sublimes as yellow phosphorus which is highly unstable and tends to explode on reheating . Farges attempted to overcome this problem by using a dual heating system for his injector and crucible (4]. We have chosen to modify an approach first used by CrystaComm, Inc (5], in which a quartz container holds the phosphorus and injects it into the indium. Liquid Encapsulated Czochralski (LEC) is currently the dominant method for growth of InP boules. However, because of convection currents in the melt and a large thermal gradient near the B2 0 3 /gas interface, LEC growth of III-V materials tends to result in high dislocation densities. The vertical gradient freeze (VGF) method has been used to surmount these problems [6], but in-situ synthesis prior to crystal growth is difficult. We are exploring the Liquid Encapsulated Kyropoulos (LEK) technique [7,8] because it combines many of the attractive features of LEC and VGF growth. Like LEC, LEK is top-seeded, so in-situ synthesis followed by crystal growth is practical. Like VGF, LEK is not characterized by large thermal gradients:
Mat. Res. Soc. Symp. Proc. Vol. 163. c1990 Materials Research Society
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the LEK crystal is
never pulled through the B2 0 3 encapsulant.
Undoped indium phosphide crystals were gr
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