Silicon doping of InP, GaAs, In0.53Ga0.47As and In0.49Ga0.51P grown by gas source and metalorganic molecular beam epitaxy using a SiBr4 vapor source

Silicon is the preferred n-type dopant for InP- and GaAs-based device structures due to its low thermal diffusivity and the absence of any surface segregation and memory effect during epitaxial growth. While the use of elemental Si in a standard effusion cell has proven effective for Si doping in gas source molecular beam epitaxy (GSMBE), this method is incompatible with the metalorganic molecular beam epitaxy (MOMBE) growth technique (metalorganic group m and hydride group V sources) due to the formation of a passivating “crust” of C and SiC on the hot Si surface in the presence of metalorganic byproducts. The formation of this crust reduces the effective surface area of the elemental Si charge and subsequently reduces the doping efficiency of the effusion cell. While elemental Sn does not form a carbide and therefore would appear to be an alternative elemental dopant source for MOMBE, anomalous doping behavior, surface segregation and memory effects limit the usefulness of this source as well as its metalorganic compound Sn(C₂H₅)₄. Other vapor sources of Si that have been investigated for doping in GSMBE and MOMBE are SiH₄ and Si₂H₆. However, SiH₄ requires precracking for efficient incorporation in GaAs. Since InP and In_0.53Ga_0.47As are typically grown at substrate temperatures approximately 100°C lower than those employed for GaAs, precracking of SiH₄ would also be required with these materials. While Si₂H₆ is less thermally stable than SiH₄, and therefore should crack more efficiently at the growth temperatures employed for InP-based growth by beam epitaxy techniques, its use has been only moderately successful. Using a 10% mixture of Si₂H₆ in H₂ and a flowrate of 10 sccm, Ando and coworkers were only able to obtain a maximum doping concentration of n=1.4×10¹⁸ cm^-3 in InP grown over the substrate temperature range of 450 to 540°C . Hence a high-efficiency gaseous Si doping source is needed in order for the full advantages of MOMBE to be realized