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abstract: Epitaxial heterostructures based on oxide perovskites and III V, II VI and transition metal dichalcogenide semiconductors form the foundation of modern electronics and optoelectronics 1 7 Halide perovskites an emerging family of tunable semiconductors with desirable properties are attractive for applications such as solution processed solar cells, light emitting diodes, detectors and lasers 8 15 Their inherently soft crystal lattice allows greater tolerance to lattice mismatch, making them promising for heterostructure formation and semiconductor integration 16 17 Atomically sharp epitaxial interfaces are necessary to improve performance and for device miniaturization. However, epitaxial growth of atomically sharp heterostructures of halide perovskites has not yet been achieved, owing to their high intrinsic ion mobility, which leads to interdiffusion and large junction widths 18 21 and owing to their poor chemical stability, which leads to decomposition of prior layers during the fabrication of subsequent layers. Therefore, understanding the origins of this instability and identifying effective approaches to suppress ion diffusion are of great importance 22 26 Here we report an effective strategy to substantially inhibit in plane ion diffusion in two dimensional halide perovskites by incorporating rigid p conjugated organic ligands. We demonstrate highly stable and tunable lateral epitaxial heterostructures, multiheterostructures and superlattices. Near atomically sharp interfaces and epitaxial growth are revealed by low dose aberration corrected high resolution transmission electron microscopy. Molecular dynamics simulations confirm the reduced heterostructure disorder and larger vacancy formation energies of the two dimensional perovskites in the presence of conjugated ligands. These findings provide insights into the immobilization and stabilization of halide perovskite semiconductors and demonstrate a materials platform for complex and molecularly thin superlattices, devices and integrated circuits. An epitaxial growth strategy that improves the stability of two dimensional halide perovskites by inhibiting ion diffusion in their heterostructures using rigid p conjugated ligands is demonstrated, and shows near atomically sharp interfaces.
author_names: Enzheng Shi

Biao Yuan

Stephen B Shiring

Yao Gao

Yunfan Guo

Cong Su

Minliang Lai

Peidong Yang

Jing Kong

Brett M Savoie

Yi Yu

Letian Dou
title: Two dimensional halide perovskite lateral epitaxial heterostructures
venue: Nature
year: 2020

abstract: Using detailed first principles calculations, we investigated the behaviour of interface vacancies in a lateral heterostructure (LHS) constructed by arsenene (As) and antimonene (Sb) which has been demonstrated to have many unique properties but with a large lattice mismatch [Q. Sun, Y. Dai, Y. Ma, N. Yin, W. Wei, L. Yu and B. Huang, 2D Mater. 2016, 3, 035017] Our calculated results show that the energetics, kinetics and electronic properties of the atomic vacancies are greatly modified at the interface of the As Sb LHS. Two mechanisms are demonstrated to govern the migration of interfacial DV 585s based on the dissociation/recombination of SVs and the exchange of atoms adjacent to the vacant sites, respectively. DV 5 585 is identified as the lowest energy atomic vacancy at the interface. The easy formation of DV 5 585 due to the release of the compressed stress in the Sb block suggests that, in LHSs with a large lattice mismatch, much attention should be paid to the potentially large concentration of detrimental interfacial vacancies close to the compressed building blocks, where the proper selection of temperature and careful control of the atomic chemical potential are essential. Meanwhile the unexpected half metal states induced by DV 3 585 o and DV 4 585 o rooted in the unpaired As atoms driven by the tensile stress reveal that decorating atomic vacancies in the stretched building blocks may provide an effective way to achieve the functionalization of LHSs with a large lattice mismatch. In addition, we reveal a single atom triggered transition between the metal and semiconductor in SV As 1 decorated As Sb LHS. Thus, by manipulating the Sb atom at the interface, the defect of SV As 1 may be used as an atomic switch to control the on off states of a circuit at the nanoscale, making As Sb LHS a promising candidate for application in nanoelectronic devices. Our theoretical work enriches the fundamental understanding of intrinsic defects at the interface of As Sb LHSs, and provides significant insight towards defect and interface engineering in LHSs with a large lattice mismatch, which are of great relevance for the manipulation of the LHS properties for the design of novel nanodevices.
author_names: Lei Ao

Zhihua Xiong
title: Insights into the vacancy behaviour at the interface of As Sb lateral heterostructures
year: 2020

abstract: Lateral TMD heterostructures create atomically thin p n junctions. These 1D interfaces offer tremendous potential to probe effects such as ultrafast charge transfer, strong coupling and strain at the interface [4 5] A particularly interesting heterostructure is Type II MoS2/ WS2. MoS2 and WS2, due to very small lattice mismatch (1.3% form clean and smooth zig zag interfaces over large areas [6]
author_names: Sandhya Susarla

Luiz H G Tizei

Steffi Y Woo

Alberto Zobelli

Odile Stephan

Pulickel M Ajayan
title: Low Loss EELS of Lateral MoS2/WS2 Heterostructures
venue: Microscopy and Microanalysis
year: 2019

abstract: We demonstrate that 3.5% in plane lattice mismatch between GaN (0001) epitaxial layers and SiC (0001) substrates can be accommodated without triggering extended defects over large areas using a grain boundary free AlN nucleation layer (NL) Defect formation in the initial epitaxial growth phase is thus significantly alleviated, confirmed by various characterization techniques. As a result, a high quality 0.2 mm thin GaN layer can be grown on the AlN NL and directly serve as a channel layer in power devices, like high electron mobility transistors (HEMTs) The channel electrons exhibit a state of the art mobility of >2000 cm2/V s, in the AlGaN/GaN heterostructures without a conventional thick C or Fe doped buffer layer. The highly scaled transistor processed on the heterostructure with a nearly perfect GaN SiC interface shows excellent DC and microwave performances. A peak RF power density of 5.8 W/mm was obtained at VDSQ 40 V and a fundamental frequency of 30 GHz. Moreover, an unpassivated 0.2 mm GaN/AlN/SiC stack shows lateral and vertical breakdowns at 1.5 kV. Perfecting the GaN SiC interface enables a GaN SiC hybrid material that combines the high electron velocity thin GaN with the high breakdown bulk SiC, which promises further advances in a wide spectrum of high frequency and power electronics.We demonstrate that 3.5% in plane lattice mismatch between GaN (0001) epitaxial layers and SiC (0001) substrates can be accommodated without triggering extended defects over large areas using a grain boundary free AlN nucleation layer (NL) Defect formation in the initial epitaxial growth phase is thus significantly alleviated, confirmed by various characterization techniques. As a result, a high quality 0.2 mm thin GaN layer can be grown on the AlN NL and directly serve as a channel layer in power devices, like high electron mobility transistors (HEMTs) The channel electrons exhibit a state of the art mobility of >2000 cm2/V s, in the AlGaN/GaN heterostructures without a conventional thick C or Fe doped buffer layer. The highly scaled transistor processed on the heterostructure with a nearly perfect GaN SiC interface shows excellent DC and microwave performances. A peak RF power density of 5.8 W/mm was obtained at VDSQ 40 V and a fundamental frequency of 30 GHz. Moreover, an unpassivated 0.2 mm GaN/A.
author_names: Jr-Tai Chen

Johan Bergsten

Jun Novi Lu

Erik Janzen

Mattias Thorsell

Lars Hultman

Niklas Rorsman

O Kordina
title: A GaN SiC hybrid material for high frequency and power electronics
year: 2018

abstract: We have proposed a 1.3 mm wavelength InGaAs(P)/InGaP double heterostructure laser that increases the band gap difference by using a wide band gap InGaP cladding layer. Epitaxial lateral overgrowth (ELO) has been investigated with liquid phase epitaxy to produce a high crystal quality ternary InGaP layer that has a large lattice mismatch on a GaAs (111)B substrate. In a previous study, we were able to produce a large area of In 0.8 Ga 0.2 P on a GaAs (111 )B substrate. However, there were a number of cracks and the crystal quality of the epitaxial layer was poor. In this study, we succeeded in reducing the number of defects in ELO layers by using a spin on diffusion source instead of a sputtering SiO 2 mask for ELO. We also attempted to grow a second InGaP layer over the first InGaP ELO layer. We were able to obtain an InGaP epitaxial layer with a mismatch to the GaAs substrate.
author_names: Shigeo Hayashi

Maki Nangu

Tomoaki Morikuni

Soichi Owa

N Shin-ichi Takahashi
title: Lattice mismatched InGaP/GaAs (111)B liquid phase epitaxy with epitaxial lateral overgrowth
year: 2009

abstract: We report on the fabrication of a near broken InAs/Al0.5Ga0.5Sb vertical TUNNEL field effect transistor (TFET) The epitaxial structure is grown on a GaAs (001) substrate thanks to large mismatch accommodation at the GaSb/GaAs interface. The fabrication process involves an anisotropic and selective wet chemical etching of the InAs channel to form a V shaped mesa with lateral side gates. This new architecture provides a large ON current at room temperature while enabling an efficient pinch off thanks to a reduced body thickness near the tunneling interface. With low temperature measurements, we identify the different mechanisms limiting the subthreshold slope at room temperature. At 77 K, where the impact of defects is reduced, a minimum subthreshold slope of 71 mV/decade is achieved for VDS 0.1 V with an ION/IOFF current ratio larger than 6 decades demonstrating that a good trade off between ON current and switching efficiency could be obtained with a near broken gap heterostructure based n TFET.
author_names: V K Chinni

M Zaknoune

C Coinon

Laurence Morgenroth

David Troadec

Xavier Wallart

Ludovic Desplanque
title: V Shaped InAs/Al0.5Ga0.5Sb Vertical Tunnel FET on GaAs (001) Substrate With I $_{\text {ON}\text {433}\mu$ A. \mu$ m \text {1} at V $_{\text {DS} \text {0.5} V
venue: IEEE Journal of the Electron Devices Society
year: 2017

author_names: Lianbi Li
title: Growth Mode and Characterization of Si/SiC Heterostructure of Large Lattice Mismatch
year: 2018

abstract: Photocarrier recombination remains a big barrier for the improvement of solar energy conversion efficiency. For 2D materials, construction of heterostructures represents an efficient strategy to promote photoexcited carrier separation via an internal electric field at the heterointerface. However, due to the difficulty in seeking two components with suitable crystal lattice mismatch, most of the current 2D heterostructures are vertical heterostructures and the exploration of 2D lateral heterostructures is scarce and limited. Here, lateral epitaxial heterostructures of BiOCl Bi2 O3 at the atomic level are fabricated via sonicating assisted etching of Cl in BiOCl. This unique lateral heterostructure expedites photoexcited charge separation and transportation through the internal electric field induced by chemical bonding at the lateral interface. As a result, the lateral BiOCl Bi2 O3 heterostructure demonstrates superior CO2 photoreduction properties with a CO yield rate of about 30 umol g 1 h 1 under visible light illumination. The strategy to fabricate lateral epitaxial heterostructures in this work is expected to provide inspiration for preparing other 2D lateral heterostructures used in optoelectronic devices, energy conversion, and storage fields.
author_names: Li Wang

Xue Zhao

Dongdong Lv

Chuangwei Liu

Weihong Lai

Chunyi Sun

Zhongmin Su

Xun Xu

Weichang Hao

Shi Xue Dou

Yi Du
title: Promoted Photocharge Separation in 2D Lateral Epitaxial Heterostructure for Visible Light Driven CO2 Photoreduction.
venue: Advanced materials
year: 2020

abstract: Electrical generation and detection of pure spin currents without the need of magnetic materials are key elements for the realization of full electrically controlled spintronic devices. In this framework, achieving a large spin to charge conversion signal is crucial, as considerable outputs are needed for plausible applications. Unfortunately, the values obtained so far have been rather low. Here we exploit the spin Hall effect by using Pt, a non magnetic metal with strong spin orbit coupling, to generate and detect pure spin currents in a few layer graphene channel. Furthermore, the outstanding properties of graphene, with long distance spin transport and higher electrical resistivity than metals, allow us to achieve in our graphene/Pt lateral heterostructures the largest spin to charge output voltage at room temperature reported so far in the literature. Our approach opens up exciting opportunities towards the implementation of spin orbit based logic circuits and all electrical control of spin information without magnetic field.Spintronic devices with full electrical control rely on electrical generation and detection of spin currents in the absence of magnetic materials. Here, the authors use Pt, a non magnetic metal, to generate and detect pure spin currents in a few layer graphene channel, achieving a remarkable spin to charge voltage signal at room temperature.
author_names: Wenjing Yan

Edurne Sagasta

M'ario Ribeiro

Yasuhiro Niimi

Luis E Hueso

Felix Casanova
title: Large room temperature spin to charge conversion signals in a few layer graphene/Pt lateral heterostructure
venue: Nature Communications
year: 2017

abstract: The synthesis of lateral heterostructures assembled by atomically thin materials with distinct intrinsic properties is important for future heterojunction embedded two dimensional (2D) devices. Here we report an etching assisted chemical vapor deposition method to synthesize large area continuous lateral graphene/hexagonal boron nitride (Gr/h BN) heterostructures on carbon containing copper foils. The h BN film is first synthesized on the copper foil, followed by hydrogen etching, and then epitaxial graphene domains are grown to form continuous lateral heterostructures. Analyses, including Raman spectroscopy, atomic force microscopy, scanning electron microscopy, x ray photoelectron spectroscopy, and ultraviolet visible absorption spectroscopy, are used to characterize the coexistence of both materials and the highly continuous nature of this lateral heterostructure. This facile and scalable synthesizing method enables the potential usage of Gr/h BN heterostructure in both fundamental studies and related 2D devices.
author_names: Pingping Zhuang

Weiyi Lin

Harry Chou

Anupam Roy

Weiwei Cai

Sanjay K Banerjee
title: Growth of lateral graphene/h BN heterostructure on copper foils by chemical vapor deposition.
venue: Nanotechnology
year: 2019