Abstract
The electron spin dynamics in a GaAs/AlGaAs heterojunction system containing a high-mobility two-dimensional electron gas (2DEG) have been studied in this paper by using pump–probe time-resolved Kerr rotation experiments. Owing to the complex layer structure of this material, the transient Kerr response contains information about electron spins in the 2DEG, an epilayer and the substrate. We analyzed the physics that underlies this Kerr response, and established the conditions under which it is possible to unravel the signatures of the various photo-induced spin populations. This was used to explore how the electron spin dynamics of the various populations depend on the temperature, magnetic field and pump-photon density. The results show that the D'Yakonov–Perel' mechanism for spin dephasing (by spin–orbit fields) plays a prominent role in both the 2DEG and bulk populations over a wide range of temperatures and magnetic fields. Our results are of importance for future studies on the 2DEG in this type of heterojunction system, which offers interesting possibilities for spin manipulation and control of spin relaxation via tunable spin–orbit effects.
Highlights
To isolate the signal from each population
We show that the response from the heterostructure can always be described as a superposition of signals from two independent electron populations, and we confirm that this is true both for the Kerr signals and for time-resolved reflectance signals that give us insights into carrier dynamics of the populations
To highlight the Kerr response that is characteristic of the heterostructure, we compare it to Kerr measurements on the bulk n-GaAs sample that were obtained under identical conditions
Summary
Our measurement technique relies on using a pump pulse that inserts optically oriented electron-spin populations well above the bottom of the conduction band, and subsequent momentum relaxation and diffusion of carriers can result in intractable Kerr signals. The g-factor of the 2DEG is well separated from that of the bulk layers, and our results show that the 2DEG population can be studied as an independent population when the density of photo-excited carriers does not exceed the 2DEG electron density from doping. The effective g-factor for the uppermost i-GaAs layer acquires a less negative value (equation (1)) than that of the underlying substrate This can be applied in a regime where the density of photo-excited carriers exceeds the 2DEG electron density from doping, and under these conditions the signal from the 2DEG is suppressed by strong band filling in the 2DEG layer. In order to confirm that we correctly assign each of the observed g-factors to a particular population in the heterostructure, we study how the g-factor, spin dephasing time and carrier lifetime of each population depend on pump-photon density and temperature
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