Charge and spin dynamics in a two-dimensional electron gas

Abstract

A number of time-resolved optical experiments probing and controlling the spin and charge dynamics of the high-mobility two-dimensional electron gas in a GaAs/AlGaAs heterojunction are discussed. These include time-resolved reflectivity, luminescence, transient grating, magneto-optical Kerr effect, and electro-optical Kerr effect experiments. The optical experiments provide information on the carrier lifetimes and spin dephasing times, as well as on the carrier diffusion coefficient which directly gives the charge mobility. A combination of the two types of Kerr experiment proves to be useful in extracting both the carrier lifetimes and spin dephasing times in a single experiment.

Optical probing of spin dynamics of two-dimensional and bulk electrons in a GaAs/AlGaAs heterojunction system

“…At later delays a longer lived (2-3 ns) negative contribution dominates the signal. This is consistent with the photoluminescence results 43 if we assign the positive short-lived contribution to the substrate, and the negative long-lived contribution to the 2DEG layer. Going to higher pump intensities, the relative weight of the negative contribution (ratio |A 2 /A 1 |, with A 2 the amplitude of the negative contribution) increases from ∼ 0.5 to ∼ 5.…”

“…Electron transport experiments on the 2DEG at 4.2 K, after illumination, gave 2.7 • 10 6 cm 2 /Vs for electron mobility, and 4.7 • 10 11 cm −2 for the electron density. We obtained nearly identical values with optical studies on our 2DEG material 43 .…”

“…Obviously, recombination also results in loss of Kerr signal, especially in undoped samples or under conditions where the photoexcited electron density exceeds the electron density due to doping 26 . With time-and spectrally-resolved photoluminescence, we measured that the exciton recombination time for our 2DEG sample at 4.2 K is greater than 2 ns in the accumulation layer, while it is approximately 360 ps for the substrate 43 . Both of these timescales become shorter with increasing pump intensity.…”

Spin dynamics in semiconductors

“…The excitation density dependence of spin relaxation was investigated in Refs. [66,514,[606][607][608][609][610][611][612]. Interestingly, it was discovered that the spin lifetime decreases with excitation density at low temperature in n-doped quantum wells [66,608,610].…”

Compact cryogenic Kerr microscope for time-resolved studies of electron spin transport in microstructures

“…The operation of the Kerr microscope is demonstrated by measuring the time-resolved Kerr rotation (TRKR) response of a GaAs/AlGaAs heterojunction structure containing a two-dimensional electron gas (2DEG). Detailed description of the material was given elsewhere 7 . Briefly, the substrate is a [001] oriented i -GaAs crystal.…”