Minority Carrier Lifetimes in Molecular Beam Epitaxy Grown AlxGa1-xAs/GaAs Double Heterostructures Doped with Aluminum

Both Al-treated pBN crucibles and A1-doped Ga melts have been used to reduce Ga-cell related oval defect densities in molecular beam epitaxy (MBE) grown epilayers. This practice., although effective in reducing the oval defect density, results in small amounts of A1 contamination in the grown films. In this work, we have grown diagnostic Al_0.3Ga_0.7As/GaAs double heterostructure (DH) devices doped with A1 in order to determine the effect of Al contamination on the minority-carrier lifetime. The active region of the DH structures was doped with Al at 5x10¹⁸ atoms/cm³ to emulate the levels observed when Al-treated pBN crucibles are used. Al impurity levels and distribution profiles were characterized by secondary ion mass spectrometry, and minority-carrier lifetimes of DH devices were characterized using time-resolved photoluminescence (PL) measurements. Device structures grown with various GaAs active layer thicknesses were used to calculate the interface recombination velocity (S) and the bulk lifetime (τ_B). We found that Al doping of the GaAs active layer adversely affects the measured PL decay time. GaAs active layers of DH devices doped with Al exhibited poor bulk lifetimes (τ_B≤120 ns) limited by Shockley-Read-Hall recombination. In contrast, DH devices grown with Al-free active layers resulted in significantly improved PL decay times with bulk lifetimes as high as τ_B= 700 ns.