Professor Ryu's Research Group
Nano-photonics Laboratory
Research:
Nano-photonics Lab works on the advanced research into novel material properties, optical/electrical devices, and energy applications of semiconductors and their nano structures. In particular, we are targeting compound semiconductors such as GaN, ZnO, which are important materials for high bandgap photonic, high power electronics, and solar energy harvesters. We study from the material growth/synthesis, fab process, characterization, to the device fabrication. Along the way, we will grow a competent researcher both in academia and industry to contribute to the semiconductor society, both in academia and industry.
Piezoelectric Nanogenerators
We are utilizing gallium nitride (GaN) based nanostructures in piezoelectricity. We are growing single crystal GaN thin film (TF) on sapphire and GaN nanowires (NWs) on sapphire, on GaN TF, and on metal substrates (Cu and Tungsten) using MOCVD (CCS-FT 19 x 2 inch, Aixtron). GaN with wurtzite crystal structure is an excellent piezoelectric semiconducting material. Based on the realistic applications we have fabricated rigid and flexible piezoelectric nanogenerators using GaN TF and NWs. It is well known that the existence of free carriers even in undoped GaN degrades the piezoelectric performance by screening the piezoelectric polarization. We succeeded to significantly suppress the internal screening effect and proposed transparent and super flexible piezoelectric nanogenerators. To enhance the overall piezoelectric performance, we have utilized the nanoporous GaN TF, GaN/V2O5 core-shell NWs, GaN/Cu2O core-shell NWs, GaN/Al2O3 core-shell NWs, and coaxial GaN NWs with p-n homojunction. Please refer to our publications for the details.
Photoelectrochemical (PEC) water splitting
GaN for PEC: We are interested in the PEC properties of single crystalline wide-band gap semiconductor such as GaN. Being a promising LED materials GaN is one of the potential candidate for unassisted PEC water splitting due to its staggered band alignment with water redox level. However being wide band-gap material it is difficult for GaN to harvest the light from visible spectrum. To mitigate this problem we are tuning the band gap of GaN by incorporating In impurities and to make it visible active. Moreover, to stabilize the GaN we have utilizing non-corrosive protective layer such as ZnS. Moreover, we are utilizing the hot electron transport phenomena from noble metals such as Au to enhance the PEC performance of GaN thin film as well as GaN NWs. Please refer to our publications for the details.
ZnO for PEC: Along with GaN, ZnO is also considered as potential candidate for PEC water splitting due to its band alignment with the water redox level. However, larger band gap prohibits absorption in the visible light region and results in a low conversion efficiency for PEC water splitting. We have fabricated ZnO NWs on various substrate using home made MOCVD for PEC water splitting reactions. Furthermore, to enhance its PEC performance we have utilized novel approach of fabrication of Single step ZnO/ZnS hierarchical structure. Please refer to our publications for the details.
Integration of Si NWs with GaN, ZnO and other earth abundant materials for various applications
Integration of SiNWs with earth abundant materials for energy storage: We have developed a technique to fabricate Si NWs from pattern assisted metal assisted chemical etching for all kind of degenerately doped Si wafers (n and p). Then we have deposited earth abundant materials such as NiCoO, MnO2 to fabricate higher energy supercapacitor electrodes.
Integration of SiNWs with GaN for carrier dynamics: Integration of III-V material with Si NWs is one of the important topic to study the carrier dynamics. We have developed a hierarchical structure of GaN NWs on SiNWs to study the carrier dynamics.
Integration of SiNWs with ZnO for novel applications: Similar to GaN we are interested to develop the hierarchical structure of ZnO NWs on Si NWs for the PEC water splitting and other novel applications. Please refer to our publications for the details.