Electrical and optical properties of undoped GaSb grown by molecular beam epitaxy using cracked Sb 1 and Sb 2

Abstract

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°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°C show p-type conductivity with a room-temperature hole mobility and hole concentration of ∼730 cm 2 v −1 s −1 and ∼3×10 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°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°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 ∼809.4 meV (4 K) is observed in the samples grown with Sb 1 at 550°C, indicating a greatly reduced density of nonradiative recombination centers.