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

Abstract

Illumination is performed at low temperature on dopant-free two-dimensional electron gases (2DEGs) of varying depths, under unbiased (gates grounded) and biased (gates at a positive or negative voltage) conditions. Unbiased illuminations in 2DEGs located more than 70 nm away from the surface result in a gain in mobility at a given electron density, primarily driven by the reduction of background impurities. In 2DEGs closer to the surface, unbiased illuminations result in a mobility loss, driven by an increase in surface charge density. Biased illuminations performed with positive applied gate voltages result in a mobility gain, whereas those performed with negative applied voltages result in a mobility loss. The magnitude of the mobility gain (loss) weakens with 2DEG depth, and is likely driven by a reduction (increase) in surface charge density. Remarkably, this mobility gain/loss is fully reversible by performing another biased illumination with the appropriate gate voltage, provided both n-type and p-type Ohmic contacts are present. Experimental results are modeled with Boltzmann transport theory, and possible mechanisms are discussed.

An Optical Technique to Produce Embedded Quantum Structures in Semiconductors

“…Once again, one can see that the observed growth of as a function of cannot be described over the full interval by a linear function, i.e., , which implies that a more complex mechanism governs this process—it is not just a strong interband absorption with one type of impurities involved [ 31 , 32 ]. One possible mechanism may be described as follows: (i) the VIS light is strongly absorbed in the AlGaAs barrier layers and produces electron-hole pairs near the δ-doping layers containing DX centers; (ii) some of the photo-generated holes are captured by DX centers, change their charge states and consequently create a periodic distribution of immobile positive charges in the δ-doping layers with a periodic spatial distribution that follows the light pattern; (iii) the unpaired free electrons drift towards and are eventually captured by the QW increasing of the 2DEG.…”

“…Once again, one can see that the observed growth of 𝑛 as a function of 𝐹 cannot be described over the full interval by a linear function, i.e., f3 = 1.685 + 3.2 × 10 𝐹, which implies that a more complex mechanism governs this process-it is not just a strong interband absorption with one type of impurities involved [31,32]. One possible mechanism may be described as follows: (i) the VIS light is strongly absorbed in the AlGaAs barrier layers and produces electron-hole pairs near the δ-doping layers containing DX centers; 7a; n s = 2.16 × 10 11 cm −2 according to the data point 5 in Figure 7b.…”

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

“…13,14 Figure 2 n 2D = 2.5 × 10 11 cm −2 in G1. The decrease in mobility at higher densities is attributed to increasing interface roughness scattering 26,27 as the electron wavefunction is pulled closer to the surface by the increasing electric field of the top-gate. Increased scattering from a populating second subband is ruled out, since there is only one subband populated over that range of density.…”