SURFACTANT-GROWN LOW-DOPED GERMANIUM LAYERS ON SILICON WITH HIGH ELECTRON MOBILITIES

We present the first investigation of the electrical properties (elect ron Hall mobilities and concentrations) of 1-mu m thick relaxed Ge lay ers grown by surfactant-mediated epitaxy (SME) with the surfactant Sb on Si(111) substrates at growth temperatures between 640 degrees C and 720 degrees C. We found that with rising growth temperatures the Ge l ayer quality improves as is demonstrated by the mobility increases at 300 K and 77 K. A record high electron mobility of 3100 cm(2)/Vs at 30 0 K (12 300 cm(2)/Vs at 77 K) which is close to the Ge lattice mobilit y was measured in the 720 degrees C layer together with an electron co ncentration of 1.1 x 10(16) cm(-3). This was derived from a differenti al Hall analysis and is identical to an interpolation value obtained f rom a comparison with high-qualify bulk Ge mobility data. A secondary ion mass spectroscopy (SIMS) analysis yielded a concentration below th e detection limit of 2 x 10(17) cm(-3) Sb. Our results demonstrate an Sb background doping reduction of three orders of magnitude in SME-gro wn Ge/Si layers compared to earlier reports. We interpret this as bein g due to an enhanced surfactant segregation without kinetic limitation s at high growth temperatures. The high quality, low doping and high m obility of these Ge layers suggests an exciting potential for future d evice applications. (C) 1998 Elsevier Science S.A. All rights reserved .