Distinguishing persistent effects in an undoped GaAs/AlGaAs quantum well by top-gate-dependent illumination

Abstract

Persistent photoconductivity of GaAs/AlGaAs heterostructures has hampered the measurement of charge- and spin-related quantum effects in gate-defined quantum devices and integrated charge sensors due to Si-dopant-related deep donor levels (DX centers). In this study, this effect is overcome by using an undoped GaAs/AlGaAs heterostructure for photonic purposes. We also measure the electron transport before and after LED illumination at low temperatures. In addition to a regular rapid saturation showing the increased carrier density, a slow accumulation of illumination effects appeared when different top-gate voltages were applied during illumination, which indicated the redistribution of charge at the oxide–GaAs interface. This study provides interesting insights into the development of optically stable devices for efficient semiconductor quantum interfaces.

Effects of biased and unbiased illuminations on two-dimensional electron gases in dopant-free GaAs/AlGaAs

“…Their observations of increased post-illumination mobility on dedicated Hall bars are consistent with the data shown here. Likewise, a mobility increase after illumination was also observed in the other illumination study on HIGFETs [35], with their 2DEG located 115 nm below the surface.…”

“…With metal gates in dopant-free HIGFETs, such screening does not occur. Charged traps inside or at the interface between the amorphous gate dielectric (SiO 2 or polyimide) and the GaAs cap layer can affect V th , as well as any surface treatment immediately prior to gate dielectric deposition [35].…”

“…IV B, "biased illumination"). In their study of illumination in HIGFET devices, Fujita et al [35] observed V th decreased ( V th < 0) after a single, long illumination at a wavelength of 780 nm (∼1.6 eV, less than the AlGaAs band gap). This is the opposite trend to what we observe.…”

“…Illumination has been studied in SISFETs, but with conflicting reports [10,13,34]. The effect had not been studied in HIGFETs, 1 until very recently [35]. Understanding the effects of biased illumination is particularly relevant for the recently active field of photon spin devices in quantum optoelectronics.…”

Field effect two-dimensional electron gases in modulation-doped InSb surface quantum wells

“…Agreement between the pinchoff voltage (V g = 0.38 V) from the two-terminal measurement and the extrapolated 2DEG turn-on threshold (V g = 0.38 V) from the four-terminal measurement, both obtained from the same Hall bar, strongly indicates that there is no significant tunnel barrier within the Ohmic contacts themselves. 25 Indeed, the electron density in the InSb quantum well directly underneath the Ohmic contact metal should be the same as or very similar to the as-grown electron density, because the HfO 2 dielectric is not in direct contact with n-InSb (i.e., there is not a large trapped charge density). The pinch-off curves are stable and reproducible, overlapping perfectly when V g is swept in the same direction and showing minimal hysteresis when V g is swept in opposite directions.…”