ON THE DETERMINATION AND CONTROL OF FLATS LOCATION IN LIQUID-ENCAPSULATED CZOCHRALSKI-GROWN INP WAFERS

The importance of the distinction between (110) directions on the surface of(100)-oriented wafers for epitaxial growth and device fabrication is well known. The distinction is made by means of two flats. The traditional methods used for the accurate determination of flats location on ingots or wafers (with X-ray diffraction) or for the qualitative distinction between the fiats (H2SO4 etchant) are compared with alternative procedures found in literature and/or developed in the present work: the use of dislocation-related etch pits (DREPs) revealed by the ''Chu et al.'' etchant and of the brightness and geometry of the faces on the cone of growth. Studies conducted on doped and undoped InP, by using optical and scanning electron microscopy, indicate that (i) concerning the cone of growth, the result differs from that typically used for GaAs and (ii) concerning the ''Chu et al.'' etchant, it originates well-defined pyramids with a rectangular base having its longer side parallel to the [0 (1) over bar (1) over bar]-[011] axis on side A and rotated 90 degrees on side B. It is suggested that DREPs can be used quantitatively for the control of fiats location or for the determination of [0 (1) over bar (1) over bar] and [0 (1) over bar 1] directions o n wafers without flats.