GSMBE growth of GaAs at low AsH3 cracking temperatures

A series of nominally undoped GaAs layers were grown by gas source MBE (GSMBE) with an elemental Ga source and AsH3 cracked by a low pressure Ta gas cracker at cracking temperatures, Tgas, between 500 and 1100°C. For Tgas below 800°C the AsH3 flow rate was increased to maintain an As-stabilized surface. All samples were found to be p-type. The net carrier concentrations decreased linearly as Tgas was decreased from 800 to 500°C; for Tgas=800°C, μ77K=4300 cm2/V⋯s, whereas when Tgas=500°C, μ77K=6400 cm2/V⋯s. Low temperature photoluminescence (PL) on samples grown at Tgas=900°C and Tgas=500°C showed carbon to be the dominant acceptor and a much lower level of carbon incorporation at the lower gas cracking temperature. Quadrupole mass spectrometer measurements of the AsH3 pyrolysis by the gas cell indicate only partial cracking occurring for Tgas=500 to 800°C; thus, AsH3 fragments may be affecting carbon incorporation at the growth surface.