In this paper, we report on the electrical and optical properties of undoped GaSb samples grown by MBE using Sb-1 as well as Sb-2 produced in a conventional antimony cracker. We establish the existence of Sb-1 and then extract the mole fraction of Sb-1 in the antimony beam as a function of the cracking zone temperature based on a combined analysis of mass spectrometry data and ion gauge flux reading. We find that the Sb-1 mole fraction becomes greater than 90% for cracking zone temperature above 950 degrees C. A series of undoped GaSb samples are grown over a wide range of substrate temperature, V/III ratio and cracking zone temperature. The undoped GaSb samples grown at 550 degrees C show p-type conductivity with a room-temperature hole mobility and hole concentration of similar to 730 cm(2) v(-1) s(-1) and similar to 3 x 10(16) cm(-3), respectively. The hole mobility and hole concentration are essentially independent of the V/III ratio over a range of 1.2-4. Decreasing the growth temperature to 440 degrees C leads to a simultaneous decrease in hole mobility, residual hole concentration and photoluminescence intensity. Hole mobility and: hole concentration do not depend strongly on the cracking zone temperature in the range 790-1000 degrees C; however, the optical intensity of the samples grown using Sb-1 is approximately one order of magnitude stronger than those using Sb-2. Besides the commonly seen bound exciton transitions at 805 (BE1), 803 (BE2), 800 (BE3) and 796 meV (BE4), a free exciton transition at similar to 809.4 meV (4 K) is observed in the samples grown with Sb-1 at 550 degrees C, indicating a greatly reduced density of nonradiative recombination centers. (C) 1999 Elsevier Science B.V. All rights reserved.