A delta-doped quantum well system with additional modulation doping.
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In situ titled-magnetic field measurements reveal that the observed direct I-QH transition depends on the magnetic component perpendicular to the quantum well, and the electron system within this structure is 2D in nature.Furthermore, transport measurements on the 2DEG of this study show that carrier density, resistance and mobility are approximately temperature (T)-independent over a wide range of T.Such results could be an advantage for applications in T-insensitive devices.
Affiliation: Department of Physics, National Tsinghwa University, Hsinchu, 300, Taiwan. lihung@mail.ncyu.edu.tw.
ABSTRACT
A delta-doped quantum well with additional modulation doping may have potential applications. Utilizing such a hybrid system, it is possible to experimentally realize an extremely high two-dimensional electron gas (2DEG) density without suffering inter-electronic-subband scattering. In this article, the authors report on transport measurements on a delta-doped quantum well system with extra modulation doping. We have observed a 0-10 direct insulator-quantum Hall (I-QH) transition where the numbers 0 and 10 correspond to the insulator and Landau level filling factor ν = 10 QH state, respectively. In situ titled-magnetic field measurements reveal that the observed direct I-QH transition depends on the magnetic component perpendicular to the quantum well, and the electron system within this structure is 2D in nature. Furthermore, transport measurements on the 2DEG of this study show that carrier density, resistance and mobility are approximately temperature (T)-independent over a wide range of T. Such results could be an advantage for applications in T-insensitive devices. No MeSH data available. Related in: MedlinePlus |
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Mentions: In the system developed in this study, ionized Si dopants confined in a layer of nanoscale can serve as nano-scatterers close to the 2DEG. Figure 1a shows longitudinal and Hall resistivity measurements at various temperatures when the magnetic field is applied perpendicular to the plane of the 2DEG. Minima in ρxx corresponding to Landau level filling factors ν = 8, 6 and 4 are observed. On the other hand, ρxy is linear at around ν = 8 and 6, and shows only a step-like structure, not a quantized Hall plateau at around ν = 4. We can see that at the crossing field Bc, approximately 2.4 T, where the corresponding filling factor is about 10, ρxx is approximately T-independent. Near the crossing field, ρxx is close to ρxy. Therefore, we observe a low-field direct I-QH transition, consistent with existing theory and experimental results [13-16,18-22]. In order to further study this effect, the sample was tilted in situ so that the angle between the applied B and growth direction is 28.5°. Figure 1b shows ρxx and ρxy as a function of total magnetic field which is applied perpendicular to the 2DEG plane at various temperatures. The ν = 4 QH-like state is now shifted to a higher field of B approximately, 7 T. Similarly, the crossing field is shifted to a higher field of approximately, 2.9 T. The authors now re-plot the data as a function of perpendicular component of the total magnetic field, as shown in Figure 1c. It can be seen that both crossing field and the minimum in ρxx corresponding to the ν = 4 QH-like state are now the same as those shown in Figure 1a. The results therefore demonstrate that the electron system are indeed 2D in nature since all the features only depend on the B component perpendicular to the growth direction. Furthermore, the corresponding approximately T-independent point in ρxx at the crossing field is the same, despite an in-plane magnetic field of approximately 1.4 T being introduced in our tilted-field measurements. |
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Affiliation: Department of Physics, National Tsinghwa University, Hsinchu, 300, Taiwan. lihung@mail.ncyu.edu.tw.
No MeSH data available.