Abstract
Temperature (T = 40 ~ 300 K) dependence of Hall-effect analysis on the dual Si-δ-doped AlGaAs/InGaAs/AlGaAs quantum-well (QW) structures with various space layer thicknesses (tS = 5, 10 and 15 nm) was performed. An interesting hysteresis behavior of electron sheet concentration [n2D(T)] was observed for tS = 10 and 15 nm but not for tS = 5 nm. A model involving two different activation barriers encountered respectively by electrons in the active QW and by electrons in the δ-doped layers is proposed to account for the hysteresis behavior. However, for small enough tS (= 5 nm ≤ 2.5 s, where s = 2.0 nm is the standard deviation of the Gaussian fit to the Si-δ-doped profile), the distribution of Si dopants near active QW acted as a specific form of “modulation doping” and can not be regarded as an ideal δ-doping. These Si dopants nearby the active QW effectively increase the magnitude of n2D, and hence no hysteresis curve was observed. Finally, effects from tS on the T-dependence of electron mobility in active QW channel are also discussed.
Highlights
Temperature (T = 40 ~ 300 K) dependence of Hall-effect analysis on the dual Si-δ-doped AlGaAs/ InGaAs/AlGaAs quantum-well (QW) structures with various space layer thicknesses was performed
In contrast to the homogeneous bulk-doped structure[7,8,9], the uniform modulation doping in barrier layers of III–V QW structure can supply charge carriers in the undoped active channel with high mobility due to less scattering from ionized d opants[10]
The Si-δ-doping in both sides of active layer provides the 2DEG in active channel, so at first the characteristics of the doping profile NSi(y) in-depth distribution for sample with tS = 5 nm was checked by dynamic secondary ion mass spectrometer (SIMS)
Summary
For small enough tS (= 5 nm ≤ 2.5 s, where s = 2.0 nm is the standard deviation of the Gaussian fit to the Si-δ-doped profile), the distribution of Si dopants near active QW acted as a specific form of “modulation doping” and can not be regarded as an ideal δ-doping These Si dopants nearby the active QW effectively increase the magnitude of n2D, and no hysteresis curve was observed. Assume that NSD + NDD = NSi, the ratio of NDD/NSi changes with Al mole fraction x′: for x′ < 0.20, NDD/NSi = 0; and for 0.20 < x′ < 0.40, NDD/NSi increases continuously with x′25 This relation is deduced from a homogeneous Si-bulk-doped structure, it still holds in the Si-δ-doping layer due to the similar occupation behaviors of Si atoms in the group III sites as long as the concentration of Si-dopants is below degenerate doping. Based on the published d ata[26], a compromise of 15% was chosen
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