It is well known that there are many arsenic precipitates in LEC GaAs, t h e dimensions of which are 500-2000A. W e have recently found that these arsenic precipitates affect the device properties of chloride epitaxial-type MESFETS. They also affect t h e formation of small surface oval defects on MBE layers. To reduce the density of these arsenic precipitates, a multiple-wafer-annealing ( M W A ) technology has been developed in which wafers are annealed first at 1100°C and then at 950°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 t h e present paper recent works are reviewed and the mechanism of arsenic precipitation is discussed from the viewpoint of stoichiometry.
Heat treatment effects on an In-GaAs ohmic contact are reported. Our finding is that the contact resistance of In to GaAs exhibits a practically insignificant increase after a heat treatment at a temperature of up to 900 °C. Results of secondary ion mass spectroscopy analysis show that the diffusion constant of In in GaAs is 3.3×10−5 exp(−1.9/kT) cm2/s. Moreover, a thermodynamic analysis gives the result that an InGaAs layer is formed between GaAs and In during the course of the heat treatment process. It is concluded from the above two analyses that the high stability of the contact resistance we have found is attributable to the low diffusion constant of In in GaAs and to the growth of an InGaAs interfacial layer.
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