Research Topics

One-dimensional semiconductor nanostructures grown on CVD-graphene films

Vertical one-dimensional (1D) semiconductor nanostructures have attracted great interest for fabricating nanoelectronic or optoelectronic devices in a scalable and integrable platform due to their favorable properties such as high surface-to-volume aspect ratio in a small footprint. However, limitation of growth compatibility allows only specific nanomaterial-substrate combinations to support well-controlled vertical growth, significantly limiting the potential applications of the 1D nanostructures. Recently, 1D nanostructures fabricated on two-dimensional (2D) nanomaterials such as graphene have been studied as a new class of material system, where the vertical growth of 1D nanostructures can be performed on 2D nanomaterial that has been transferred onto a desired substrate prior to growth. However, the growth of 1D semiconductor nanostructures on 2D nanomaterials is still at an early stage, restricted to specific combinations of materials in small scale or with limited control of dimensions and positions. We are growing individually dimension and position control of ZnO nanostructures on graphene films and extending to the application-specific substrate with desired properties.[http://aip.scitation.org/doi/full/10.1063/1.4964490]


GaN growth on 2-dimensional layered materials using Metal-Organic Chemical Vapor Deposition (MOCVD) system


We grow GaN on 2D layered materials including graphene and hBN using MOCVD system. In general, inorganic compound semiconductors have many advantages over organic materials, including their high carrier mobility and radiative recombination rate as well as their long-term stability and reliability However, problems associated with high-quality inorganic film growth on large or flexible substrates represent one of the major obstacles to the use of inorganic semiconductors in many applications on flexible electronic optoelectronics. To address this problem, we developed growth of high quality GaN on 2D layered materials which exhibit large-scalability and flexibility. We have been interested in not only growth of GaN thin film, but also GaN microstructures including microdisk, pyramid and microrod on the 2D layered materials for their applications on flexible devices.


Homemade UHV-MBE system


We built a ultrahigh vacuum molecular beam epitaxy (UHV-MBE) system. It is designed for topological insulator and superconductor van der Waals materials growth and customized for quick operations. Ultrahigh purity Bi, Sb, Se, Te sources are provided by effusion cells. An electron beam gun is installed for Nb evaporation which requires temperature higher than 2000 degree Celsius.

 

MBE growth of high quality van der Waals heterostructures: Bi2Se3, NbSe2 and their heterostructures oh h-BN


We design and engineer heterointerfaces of 2D van der Waals (vdW) materials for the realization of novel quantum electronic states. We employ MBE combined with nanofabrication techniques to form functional nanostructures that can be utilized for new electronic device applications. In particular we focus on making devices based on high quality vdW heterostructures composed of Bi2Se3, NbSe2, and h-BN – a model topological insulator, superconductor, and normal insulator, respectively. [J. Y. Park et. al., 2D Materials (2016) https://doi.org/10.1088/2053-1583/3/3/035029]



Nanoarchitecture light-emitting diodes

Three-dimensional nanoarchitecture LEDs are attracting tremendous amount of interest as a candidate for next-generation light-emitters, since they offer huge amount of additional light-emitting area compared with planar LEDs and show many unconventional properties which were very hard to achieve with conventional LEDs. We are interested in designing new nanoarchitecture LEDs to create novel device concepts.

 

Fabrications of flexible optoelectronic devices using GaN microstructures on 2-dimensional layered materials and their applications on wearable display and bio-medical devices


Large-scale and flexible electronic and optoelectronic devices have recently attracted much attention for use in wearable displays, solar cells, sensors, and biomedical devices. For the bendable and wearable devices, organic films due to their excellent scalability and flexibility have widely been employed. Meanwhile, achieving flexible devices using inorganic films is still very challenging because of the rigidity and brittleness inherent to inorganic films and single-crystalline substrates. To resolve this problem, we have fabricated flexible inorganic LEDs using GaN microstructures grown on CVD graphene. Currently, we are interested in applications of the flexible inorganic LEDs on many rising fields such as wearable display and bio-medical devices.

 

Synthesis of the large-area, high-quality 2d materials


Our group aims synthesis of large-area, high-quality 2d nanomaterials. Especially, our group has invented centimeter-sized epitaxial h-BN film in which h-BN hexagonal lattice is oriented in single direction. We also provide high-quality graphene films which is basic building block for the 1d-2d hybrid nanomaterials.

 

Microstructural analysis of the novel heterointerface at 1d-2d hybrid nanomaterial system


We investigate the novel heteroepitaxy of semiconductor nanostructures on 2d nanomaterials. The unique combination of 2d nanomaterials with semiconductor nanostructures have enabled flexible and stretchable optoelectronics with high-performance, inorganic-based channels. The distinctive features of these heterointerfaces are of great importance to understand and develop the full potential of 1d-2d hybrid nanomaterials.

 

Fabrication of the wearable sensors


Wearable sensors are key components for the next-generation electronic devices. Our group has developed an unique process to produce flexible and stretchable sensors. The 1d-2d hybrid nanomaterial system has enabled to fabricate high performance inorganic sensors which can be detached from original substrates and can be used in devices with flexible and stretchable formfactors.

 

Novel vertical field-effect nano transistors using 1d-2d hybrid nanomaterials


Our group have created novel vertical field-effect transistors based on position- and morphology-controlled ZnO nanotube arrays on graphene substrates. This state-of-the-art technology will enable the truly flexible and stretchable integrated electronics, where high performance is no longer optional.