Anomalous spin-orbit effects in a strained InGaAs/InP quantum well structure

There currently is a large effort to explore spin-orbit effects in semiconductor structures with the ultimate goal of manipulating electron spins with gates. A search for materials with large spin-orbit coupling is therefore important. We report results of a study of spin-orbit effects in a strained InGaAs/InP quantum well. The spin-orbit relaxation time, determined from the weak antilocalization effect, was found to depend non-monotonically on gate voltage. The spin orbit scattering rate had a maximum value of $5\cdot 10^{10}\,$s$^{-1}$ at an electron density of $n=3\cdot 10^{15}\,$m$^{-2}$. The scattering rate decreased from this for both increasing and decreasing densities. The smallest measured value was approximately $10^9\,$s$^{-1}$ at an electron concentration of $n=6\cdot 10^{15}\,$m$^{-2}$. This behavior could not be explained by neither the Rashba nor the bulk Dresselhaus mechanisms but is attributed to asymmetry or strain effects at dissimilar quantum well interfaces.