GaSb ingots were oriented along the low index crystal planes, (111), (ii0), and (I00), using an optical technique. The surfaces etched with an HCI:CuCI solution show very well-defined figures, revealing the high symmetry of the surface orientations. The reflectograms obtained from these surfaces allow the precise orientation of GaSb crystals, and they can be used to distinguish between the (III)A and (III)B faces. An impor tant step in the prepara t ion of substrates, for the epi taxia l growth of layers involved in device fabr ication, is the crystal lographic orientat ion of the substrate 's surface. This can be achieved either by using xrays or an optical technique, the la t te r being faster, cheaper, and safer than the former. The perpendicular reflection of a light beam from suitably etched crystal surfaces produces figures on a screen that are known as reflectograms. The procedure used to orient crystals using such reflectograms is described in Ref. 1-4. The accuracy obtained orienting a crystal with this technique can be as good as that obtained with x-rays, Fig. 1. (100) surface of GaSb etched by a solution of 4 g CuCI in Fig. 2. (110) surface of GaSb etched by a solution of 4 g CuCI in 40 ml HCI during 40 min at 80~ 40 ml HCI during 30 min at 80~ J. Electrochem. Soc., Vol. 141, No. 8, August 1994 9 The Electrochemical Society, Inc. 2221 provided that the etch figures produced on the surface of the material clearly reflect the crystal symmetry. TM In a literature survey we have found only one etching reported for GaSb suitable for optical orientation? It consisted in the dissolution and redeposition of GaSb in molten Ga at 500~ We have found this method difficult to control, the equipment is cumbersome, and it takes a long time before one can see results. It is known 6 that etching solutions containing metallic ions produce more surface features than solutions without them. Particularly, InSb etched with a 0.4N Fe+++/6.0N HCI solution, at 82~ shows figures that are characteristic of the orientation of the crystal surface. 7 We have tried the same solution on GaSb and found that it works well for the (111) surfaces, but on the (100) planes it produces too quickly very elongated rectangles not suited for optical orientation. Instead, the etching with the CuC1 solution, that we used in this work, is easier to control, because the quality of the reflectograms is not very dependent on the etching time, especially on the (100) and (111) faces.