Polarization-induced two-dimensional electron gases in ZnMgO/ZnO heterostructures

Tampo, Hitoshi; Shibata, Hajime; Maejima, Keigou; Yamada, A.; Matsubara, Koji; Fons, Paul; Kashiwaya, Satoshi; Niki, Shigeru; Chiba, Y.; Wakamatsu, Takao; Kanie, Hisashi

doi:10.1063/1.3028338

Cited by 141 publications

(98 citation statements)

References 16 publications

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“…In order to simulate n-type/p-type carriers, we add/remove a total charge 0.001e per supercell corresponding to a surface charge density of 1 × 10 12 e/cm 2 , which is in the lower end of experimental concentrations. 25,27 The resulting charge distribution of the free carriers is obtained by summing the partial charge density of all occupied conduction band states (n-type) or all empty valence band states (p-type), n,k |φ nk | 2 , where the sum is over the corresponding bands and k-points in the Brillouin zone.…”

Section: Deg and 2dhg Charge Density Profilementioning

confidence: 99%

“…30,31 The presence of the 2DEG is normally confirmed by Hall effect and capacitance measurements. 24,27,28 The observation of the quantum Hall effect 25 and the fractional quantum Hall effect 29 in these heterostructures testifies to the high quality of these interfaces. Charge concentrations on the order of 10 13 cm −2…”

Section: Introductionmentioning

confidence: 99%

“…23 Recently, a different type of system supporting a 2DEG, wurtzite ZnO/Zn(Mg)O heterostructures, has been investigated experimentally. [24][25][26][27][28][29][30][31][32] These heterostructures are usually grown using molecular beam epitaxy; 24,25 however, a 2DEG was also demonstrated in samples grown with metal-organic vapor deposition which is suitable for mass production. 30,31 The presence of the 2DEG is normally confirmed by Hall effect and capacitance measurements.…”

Section: Introductionmentioning

confidence: 99%

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Polarization discontinuity induced two-dimensional electron gas at ZnO/Zn(Mg)O interfaces: A first-principles study

et al. 2013

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The discovery of a high-mobility two-dimensional electron gas (2DEG) in wurtzite ZnO/Zn(Mg)O heterostructures is promising for applications due to the high mobility of the carriers. In this paper, we study the formation and properties of the 2DEG at ZnO/Zn(Mg)O interfaces using first-principles calculations based on hybrid density functional theory. The 2DEG arises from the polarization discontinuity at the interface between the two materials. The uncompensated bound charge at the interface gives rise to an electric field in the bulk of ZnO which confines free carriers close to the interface. We find that the type of the confined carriers is determined by the interface termination, while the amount of charge and the confinement width could be controlled by the Mg doping and the device dimensions.

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Section: Deg and 2dhg Charge Density Profilementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Polarization discontinuity induced two-dimensional electron gas at ZnO/Zn(Mg)O interfaces: A first-principles study

et al. 2013

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“…The dependence of both polarizations on the Al concentration, for example, in AlGaN-GaN, can be studied by investigating the electronic properties of two-dimensional carrier gases, which can form at the interface. Similar investigations have been carried out in the MgZnO-ZnO system [49][50][51] where, however, the latticemismatch induced strain is smaller than in the AlGaN-GaN system, and a cubic ͑rocksalt-structure͒ phase transition occurs in Zn x Mg 1−x O for x Ϸ 0.65. 52 Experimental polarization values have been obtained by numerical evaluation of the photoluminescence shift in MgZnO-ZnO quantum well structures.…”

Section: Introductionmentioning

confidence: 72%

Interface polarization coupling in piezoelectric-semiconductor ferroelectric heterostructures

et al. 2010

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M.; Hofmann, Tino; Brandt, M.; Lorenz, M.; Grundmann, M.; Ashkenov, N.; Schmidt, H.; Ianno, Natale J.; and Schubert, Mathias, "Interface polarization coupling in piezoelectric-semiconductor ferroelectric heterostructures" (2010 We present a dielectric continuum model approach for studying the electrical polarization properties of interface polarization coupled BaTiO 3 , BaTiO 3 -ZnO, and ZnO-BaTiO 3 -ZnO thin-film structures consisting of several hundred nanometer thick layers. Our model augments the effects of electric field driven switchable polarization and depletion layer formation with spontaneous interface polarization coupling. Wurtzite-structure ͑piezoelectric͒ n-type ZnO and perovskite-structure ͑ferroelectric͒ highly insulating BaTiO 3 layers were prepared and investigated. The coupling between the nonswitchable spontaneous polarization of ZnO and the electrically switchable spontaneous polarization of BaTiO 3 causes strong asymmetric polarization hysteresis behavior. The n-type ZnO reveals hysteresis-dependent capacitance variations upon formation of depletion layers at the ZnO/BTO interfaces. We obtain a very good agreement between our model generated data and our experiment. Our model approach allows for derivation of the amount and orientation of the spontaneous polarization of the piezoelectric constituents and can be generalized toward multiple-layer piezoelectricsemiconductor ferroelectric heterostructures. We identify interface polarization coupled triple-layer ZnO-BTOZnO heterostructures as two-terminal unipolar ferroelectric Bi-junction transistor for use in memory storage.

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“…However, the concept naturally generalizes not only to nitrides, 47 including InN and BN and their alloys, but also to heterostructures of other polar materials such as ZnMgO/ZnO. 49 …”

Section: Discussionmentioning

confidence: 99%

Polarization-balanced design of heterostructures: Application to AlN/GaN double-barrier structures

2011

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Inversion and depletion regions generally form at the interfaces between doped leads (cladding layers) and the active region of polar heterostructures like AlN/GaN and other nitride compounds. The band bending in the depletion region sets up a barrier that may seriously impede perpendicular electronic transport. This may ruin the performance of devices such as quantum-cascade lasers and resonant-tunneling diodes. Here we introduce the concepts of polarization balance and polarization-balanced designs: A structure is polarization balanced when the applied bias match the voltage drop arising from spontaneous and piezeolectric fields. Devices designed to operate at this bias have polarization-balanced designs. These concepts offer a systematic approach to avoid the formation of depletion regions. As a test case, we consider the design of AlN/GaN double-barrier structures with AlxGa 1−x N leads. To guide our efforts, we derive a simple relation between the intrinsic voltage drop arising from polar effects, average alloy composition of the active region, and the alloy concentration of the leads. Polarization-balanced designs secure good filling of the ground state for unbiased structures, while for biased structures with efficient emptying of the active region they remove the depletion barriers.

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Polarization-induced two-dimensional electron gases in ZnMgO/ZnO heterostructures

Cited by 141 publications

References 16 publications

Polarization discontinuity induced two-dimensional electron gas at ZnO/Zn(Mg)O interfaces: A first-principles study

Polarization discontinuity induced two-dimensional electron gas at ZnO/Zn(Mg)O interfaces: A first-principles study

Interface polarization coupling in piezoelectric-semiconductor ferroelectric heterostructures

Polarization-balanced design of heterostructures: Application to AlN/GaN double-barrier structures

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