It is well known that there are many arsenic precipitates in LEC GaAs, the dimensions of which are 500-2000 AA. The authors have recently found that these arsenic precipitates affect the device properties of chloride epitaxial-type MESFETS. They also affect the formation of small surface oval defects on MBE layers. To reduce the density of these arsenic precipitates, a multiple-wafer-annealing (MWA) technology has been developed in which wafers are annealed first at 1100 degrees C and then at 950 degrees C. By this annealing, highly uniform substrates with low arsenic precipitate densities, uniform PL and CL, uniform microscopic resistivity distributions and uniform surface morphology after AB etching can be obtained. These MWA wafers showed low threshold voltage variations for condensed ion-implantation-type MESFETS. In the present paper recent works are reviewed and the mechanism of arsenic precipitation is discussed from the viewpoint of stoichiometry.

source:iopscience

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