Magnesium Doping Controlled Density and Mobility of Two-Dimensional Electron Gas in Mg$_{x}$Zn$_{1-x}$O/ZnO Heterostructures

Recent technological advancement in ZnO heterostructures has expanded the possibility of device functionalities to various kinds of applications. In order to extract novel device functionalities in the heterostructures, one needs to fabricate high quality films and interfaces with minimal impurities, defects, and disorder. With employing molecular-beam epitaxy (MBE) and single crystal ZnO substrates, the density of residual impurities and defects can be drastically reduced and the optical and electrical properties have been dramatically improved for the ZnO films and heterostructures with Mg x Zn 1-x O. Here, we overview such recent technological advancement from various aspects of application. Towards optoelectronic devices such as a light emitter and a photodetector in an ultraviolet region, the development of p-type ZnO and the fabrication of excellent Schottky contact, respectively, have been subjected to intensive studies for years. For the former, the fine tuning of the growth conditions to make Mg x Zn 1-x O as intrinsic as possible has opened the possibilities of making p-type Mg x Zn 1-x O through NH 3 doping method. For the latter, conducting and transparent polymer films spin-coated on Mg x Zn 1-x O was shown to give almost ideal Schottky junctions. The wavelength-selective detection can be realized with varying the Mg content. From the viewpoint of electronic devices, two-dimensional electrons confined at the Mg x Zn 1-x O/ZnO interfaces are promising candidate for quantum devices becauseof high electron mobility and strong electron-electron correlation effect. These wonderful features and tremendous opportunities in ZnO-based heterostructures make this system unique and promising in oxide electronics and will lead to new quantum functionalities in optoelectronic devices and electronic applications with lower energy consumption and high performance.

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“…Recently, we have changed the gas source from oxygen plasma to distilled pure ozone to supply contamination-free oxidizing agent. 31 …”

Section: A Reduction Of Impurities In Zno Substratementioning

confidence: 99%

“…68 and 85) and then to 180 000 cm 2 V À1 s À1 through careful optimization of the growth conditions. 28,75 Further improvement of the l was realized by the installation of pure distilled ozone (O 3 ) source in the MBE system and by the careful optimization of the Mg content in the barrier layer; 31 the l has reached to 770 000 cm 2 …”

mentioning

confidence: 99%

Challenges and opportunities of ZnO-related single crystalline heterostructures

Kozuka

Tsukazaki

Kawasaki

2014

Applied Physics Reviews

130

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“…152 When we switched from oxygen plasma to ozone as an oxidizing agent, we could further eliminate the scattering centers such as impurities. 153,154 Not only the electron mobility was enhanced dramatically but also far more fragile fractional states with larger denominators in¯c ould be detected as shown in Figure 17d. 149,155,156 The chorological progress of the sample quality is compared with that of AlGaAs/GaAs in terms of electron mobility (Figure 18).…”

Section: ¹2mentioning

confidence: 91%

Exploration of Electronic Functionalities in Metal Oxides by Combinatorial Lattice Engineering

Kawasaki

2013

Bulletin of the Chemical Society of Japan

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A review is given for our originally-developed thin film technology, "combinatorial lattice engineering." This is extended from a conventional pulsed laser deposition, where the surface of a sintered oxide tablet (target) is irradiated with focused laser pulses and the evaporated precursors are condensed on a heated substrate to grow single crystalline thin films. By this method, it has become possible to concurrently synthesize many oxide thin films on a substrate at different locations (segments) with such diversities as composition, growth conditions, and the sequence of heterostructures. By inserting a masking system between the target and substrate and computer controlling the mask motion as well as target switching, one can integrate many oxide thin film segments on the substrate. Starting from the background of and demand for this technology as well as the advancement of the key ingredient technology, i.e., atomically regulated epitaxial growth of oxide thin films, the concept and examples of this combinatorial lattice engineering are introduced highlighting the representative demonstration on magnetic, photonic, and electronic functionalities, especially emphasizing the benefit of this combinatorial technology. In addition, further progress of device physics triggered by the combinatorial discoveries are introduced, for example, electric field control of magnetism, bright ultraviolet light emitting devices, and quantum effects in oxide semiconductors.

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“…10,17 The structure of the samples consisted of 500 nm-thick ZnO buffer layer followed by a 2 nm-thick Mg x Zn 1-x O layer (0.005 ≤ x ≤ 0.4) and a 500 nm-thick Mg 0.01 Zn 0.99 O capping layer as shown in the inset of Fig. 1(a).…”

Section: Methodsmentioning

confidence: 99%

Alloy disorder modulated electron transport at MgxZn1-xO/ZnO heterointerface

et al. 2017

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High-mobility electron systems in two dimensions have been the platform for realizing many fascinating quantum phenomena at low temperatures. Continuous demand to improve the sample quality has necessitated the investigations of various disorders influencing the quantum transport. Here, we study the effect of short-ranged alloy disorder on the scattering of two-dimensional electron system in MgxZn1-xO/ZnO. For this purpose, we employ a modified interface profile consisting of Mg0.01Zn0.99O/ZnO with a thin (2nm) MgxZn1-xO interlayer with x ranging from 0.005 to 0.4. This interlayer design allows us to investigate scattering mechanisms at a nearly constant carrier density as the interlayer is found not to significantly affect the carrier density but enhance alloy disorder. While the transport scattering time (τtr) shows a strong correlation with x, the quantum scattering time (τq) remains insensitive to x. The large variation in the τtr/τq ratio (from 16.2 to 1.5 corresponding to x from 0.005 to 0.4) implies a change in the dominant scattering mechanism from long range towards short range with increasing x. The insensitivity of τq on x indicates the scattering rate is not dominated by the alloy disorder. This implies that other scattering mechanisms, likely unintentional background impurities or remote surface disorders, are dominant in limiting τq, and therefore providing a prospect for pursuing ever higher levels in the quality of the two-dimensional electron system in MgxZn1-xO/ZnO system.

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Magnesium Doping Controlled Density and Mobility of Two-Dimensional Electron Gas in Mg$_{x}$Zn$_{1-x}$O/ZnO Heterostructures

Cited by 74 publications

References 23 publications

Challenges and opportunities of ZnO-related single crystalline heterostructures

Challenges and opportunities of ZnO-related single crystalline heterostructures

Exploration of Electronic Functionalities in Metal Oxides by Combinatorial Lattice Engineering

Alloy disorder modulated electron transport at MgxZn1-xO/ZnO heterointerface

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