Fabrication of high-quality one- and two-dimensional electron gases in undoped GaAs/AlGaAs heterostructures (original) (raw)
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Journal of the Korean Physical Society, 2020
We studied the properties of electron transport in mesoscopic GaAs/AlGaAs heterostructure without any intentional dopants in which an external electric field defined the two-dimensional electron gas (2DEG). An electrically formed 2DEG without intentional doping offers many advantages because of the absence of high concentrations of charged scattering centers. We demonstrate that the electron concentration can be easily tuned by varying the gate voltage. This tunability was observed for a high-quality 2DEG with a carrier density ranging from 0.75 to 3.34 × 10 11 cm −2 , for which the corresponding mobility ranged from 0.26 to 2.93 × 10 6 cm 2 V −1 s −1. The mobility of the 2DEG is closely followed the experimental power law for high-mobility wafers, μ ∝ n 0.7 2D .
Study of internal electric fields in AlGaAs/GaAs two-dimensional electron gas heterostructures
Microelectronics Journal, 2003
Modulation-doped GaAs/AlGaAs heterostructures have been studied by photoreflectance spectroscopy. The spectra at room temperature show Franz -Keldysh oscillations associated to the substrate -buffer layer interface. The built-in electric field magnitude calculated from these oscillations is related with the two-dimensional electron gas (2DEG) mobility. In addition we observed two signals associated to the GaAs capping layer and to the 2DEG, respectively. q
Applied Physics Letters, 2010
We demonstrate a method of making a very shallow, gateable, undoped 2-dimensional electron gas. We have developed a method of making very low resistivity contacts to these structures and systematically studied the evolution of the mobility as a function of the depth of the 2DEG (from 300nm to 30nm). We demonstrate a way of extracting quantitative information about the background impurity concentration in GaAs and AlGaAs, the interface roughness and the charge in the surface states from the data. This information is very useful from the perspective of molecular beam epitaxy (MBE) growth. It is difficult to fabricate such shallow high-mobility 2DEGs using modulation doping due to the need to have a large enough spacer layer to reduce scattering and switching noise from remote ionsied dopants.
Physica E: Low-dimensional Systems and Nanostructures, 2004
The use of focused ion beam implantation doping of an inverted GaAs/Al1−xGaxAs heterostructure during a growth interruption allows for the lateral modulation of the heterostructure doping. Hence, laterally patterned two dimensional electron gases (2DEGs) are obtained with no further processing steps required. We have performed the direct writing of a 2DEG with a Hall-bar pattern, such that only the application of ohmic contacts was necessary and the sample surface remained unharmed otherwise. The 2DEG has an electron density of 3:6 × 10 11 cm −2 and an electron mobility of 4:8 × 10 5 cm 2 =V s, as determined by magnetotransport measurements. A conventional mesa-etched Hall-bar with almost identical electronic properties has also been studied. Di erent behaviour of the longitudinal as well as the transversal magnetoresistance for the two Hall-bars is observed and can be concluded to be due to a di erent conÿnement potential.
Photoluminescence from the two-dimensional electron gas at GaAs/AlGaAs single heterojunctions
Applied Physics Letters, 1988
Liquid-helium temperature photoluminescence from GaAs/Al(0.3)Ga(0.7)As modulation-doped single heterojunctions has been studied, using excitation sources from infrared to ultraviolet. The spectra have a strong interface component, accompanied by bulk GaAs and AlGaAs band-gap luminescence. Using ultraviolet instead of infrared as the excitation, the interface signal is greatly enhanced relative to the bulk GaAs luminescence. The interface signal can be shifted to the higher energies when a semitransparent front gate is positively biased. The observations indicate that the interface luminescence comes from the recombination of the two-dimensional electrons with holes trapped at or near the interface. The peaks and the shoulders in the interface spectra appear to correspond to subbands of the two-dimensional electron gas at the interface. The results demonstrate the feasibility of doing spectroscopic studies on high-mobility electrons at single heterojunctions.
Electron and hole gas in modulation-doped GaAs/Al_{1−x}Ga_{x}As radial heterojunctions
Physical Review B, 2011
We perform self-consistent Schrödinger-Poisson calculations with exchange and correlation corrections to determine the electron/hole gas in a radial hetero-junction formed in a modulation doped GaAs/AlGaAs core-multi-shell nanowire (CSNW) which is n-/p-doped. Realistic composition and geometry are mapped on an symmetry compliant two-dimensional grid, and the inversion/accumulation layers are obtained assuming mid-gap Fermi energy pinning at the surface. We show that the electron and hole gases can be tuned to different localizations and symmetries inside the core as a function of the doping level. Contrary to planar hetero-junctions, conduction electrons do not form a uniform 2D electron gas (2DEG) localized at the GaAs/AlGaAs interface, but rather show a transition between i) an isotropic, cylindrical distribution deep in the GaAs core (low doping), and ii) a set of six tunnel-coupled quasi-1D channels at the edges of the interface (high doping). Holes, on the other hand, are much more localized at the GaAs/AlGaAs interface and form either i) six separated planar 2DEGs at the GaAs/AlGaAs interfaces (low doping), ii) a quasi uniform six-fold bent 2DEG (intermediate doping), or iii) six tunnel-coupled quasi-1D channels at the edges (high doping). We also simulate the electron/hole gas in a CSNW-based field effect transistor. The field generated by a back-gate may easily deform the electron or hole gas, breaking the six-fold symmetry. Single 2DEGs at one interface or multiple quasi-1D channels are shown to form as a function of voltage intensity, polarity, and carrier type.
AlGaAs/GaAs single electron transistor fabricated without modulation doping
Applied Physics Letters, 2010
We have fabricated quantum dot single electron transistors, based on AlGaAs/GaAs heterojunctions without modulation doping, which exhibit clear and stable Coulomb blockade oscillations. The temperature dependence of the Coulomb blockade peak lineshape is well described by standard Coulomb blockade theory in the quantum regime. Bias spectroscopy measurements have allowed us to directly extract the charging energy, and showed clear evidence of excited state transport, confirming that individual quantum states in the dot can be resolved.
Journal of Crystal Growth, 1994
We present modulation-doped ordered-InGaP/disordered-InGaP homojunctions grown, lattice matched to GaAs, by metalorganic vapour phase epitaxy. Capacitance-voltage (C-V) profiling techniques, temperature-dependent Hall, Shubnikov-De Haas and photoluminescence measurements have been used for characterization. The C-V measurements show a narrow profile at the homointerface with an order of magnitude reduction in carrier density within 3 nm. From temperature dependent Hall measurements, typical two-dimensional behaviour is observed with sheet carrier densities as high as 3.6 x 1013 cm 2 (T < 100 K). No carrier freeze-out and constant mobilities around 850 cm2 V~~below T= 100 K are observed. The 300 K channel conductivity of this new type of junction is 3.2 x io~Q1, which is higher than reported in other two-dimensional electron gases. Shubnikov-De Haas measurements indicate the presence of two occupied excited subbands. The photoluminescence measurements clearly show a moving emission which involves the 2DEG.