Quantitative evaluation of substrate temperature dependence of Ge incorporation in GaAs during molecular beam epitaxy

Combined Hall effect and low-temperature photoluminescence measurements have been used to perform a thorough evaluation of the growth temperature dependence of Ge incorporation in GaAs during molecular beam epitaxy (MBE) over the entire substrate temperature range (400°≦ T _s ≦600[°C]) practicable for n-type layer growth. Using a constant As₄ to Ga flux ratio of two, growth below 500°C yields n-GaAs: Ge films having electrical and optical properties rapidly deteriorating with decreasing T _s . Growth at 500° ≦ T _s ≦600[°C] produces high-quality n-GaAs: Ge films ( N _D / N _A ≈4) with C as well as Ge residual acceptors competing on the available As sites. The amount of Ge atoms on As sites [Ge_As] increases with substrate temperature, whereas simultaneously the amount of C atoms on As sites [C_As] decreases thus leading to the well-established nonlinear behaviour of the ( N _A / N _D vs. 1/ T _s plot. Counting the incorporated Ge impurities separately, however, yields a linear behaviour of the ([Ge_As]/[Ge_Ga]) vs. 1/ T _s plot which has exactly the same slope as the ( P _{As 2}/ P _Ga) vs. 1/ T _s plot derived from vapour pressure data of As₂ and Ga over solid GaAs surfaces. The important result is, therefore, that the incorporation behaviour of Ge in GaAs during molecular beam epitaxy is directly correlated with the evaporation behaviour of the growing GaAs surface.