Shih Chia Liu

Transferrable single crystalline 4H-SiC nanomembranes

In this work, we demonstrate a transferrable single crystalline 4H-SiC nanomembrane (SiC NM) released from a SiC-on-insulator (SiCOI) wafer. High resolution X-ray diffraction (XRD) and atomic force microscopy (AFM) were performed on the SiC NM and confirmed similarly good crystallinity and surface morphology. In addition, the refractive index and extinction coefficient of the SiC NM were investigated using ellipsometry analyses. Despite its thinness (i.e., 200 nm), the SiC NM achieved an absorption greater than 40% in the wavelength range of 200–260 nm with a maximum absorption of 73.8% at 256 nm. Our transferrable SiC NM provides not only good mechanical flexibility, but also exhibits excellent ultraviolet (UV) light absorption which could be readily utilized for high sensitivity flexible UV detectors.

Light absorption enhancement in Ge nanomembrane and its optoelectronic application

In this study, the light absorption property of Ge nanomembrane (Ge NM), which incorporates hydrogen (H), in near-infrared (NIR) wavelength range was analyzed. Due to the presence of a large amount of structural defects, the light absorption coefficient of the Ge layer becomes much higher (10 times) than that of bulk Ge in the wavelength range of 1000 ~1600 nm. Increased light absorption was further measured from released Ge NM that has H incorporation in comparison to that of bulk Ge, proving the enhanced light absorption coefficient of H incorporated Ge. Finally, metal-semiconductor-metal (MSM) photodetectors were demonstrated using the H incorporated Ge on GeOI.

Polycrystalline GeSn thin films on Si formed by alloy evaporation

Polycrystalline GeSn thin films on Si substrates with a Sn composition up to 4.5% have been fabricated and characterized. The crystalline structure, surface morphology, and infrared (IR) absorption coefficient of the annealed GeSn thin films were carefully investigated. It was found that the GeSn thin films with a Sn composition of 4.5% annealed at 450 °C possessed a desirable polycrystalline structure according to X-ray diffraction (XRD) analyses and Raman spectroscopy analyses. In addition, the absorption coefficient of the polycrystalline GeSn thin films in the IR region was significantly better than that of the single crystalline bulk Ge.

Amorphous Si/SiO2 distributed Bragg reflectors with transfer printed single-crystalline Si nanomembranes

A distributed Bragg reflector (DBR) consisting of a single-crystal Si nanomembrane (NM) layer formed by the transfer printing technique on top of an evaporated amorphous Si (a-Si)/SiO2 DBR structure was demonstrated. The reflectivity of different DBR structures/pairs is measured and verified it by the simulation. An improved surface roughness of the top layer by employing a Si NM suggests that the smoother single crystalline surface not only minimizes light scattering loss but also can be an epitaxial template layer for subsequent Si growth without contributing any strain. The results indicate a simple pathway toward achieving high performance Si/SiO2 DBRs employing Si NM as a top layer. This method could also lead to the fabrication of large-area, high performance NM based DBRs at low cost with high throughput.

Nano-indented Ge surfaces by metal-assisted chemical etching (MacEtch) and its application for optoelectronic devices

Surface reflection is one of the major limiting factors to determine light absorption performance of optoelectronic devices. In recent years, light management using various types of nanostructures has gained much attention [1]. However, fabricating the nanostructures by conventional dry etching results in damage within the crystal structures attributed to high energy ions. Metal assisted chemical etching (MacEtch) is an alternative method to produce the nanostructures [2]. Because MacEtch is fundamentally a wet etch which does not involve high energy ions, structural defects can be avoided [3,4]. Therefore, the technique has been widely used to create surface texturing for the optoelectronic and photonic applications. However, the MacEtch enabled nanostructures have been mainly formed on Si and III-V compounds [5,6]. In this report, we present a novel MacEtch based technique to create nano-indentations on Ge and the enhanced responsivity and reduced dark current of Ge photodiodes.

Lateral size scaling of photonic crystal surface-emitting lasers on Si

We report here the lateral size scaling effect of the photonic crystal surface-emitting lasers (PCSELs) based on heterogeneously integrated InGaAsP MQW membranes transferred on silicon photonic crystal cavities. Lateral and vertical confinement schemes were also investigated towards low threshold lasing of PCSELs with small lateral cavity sizes.

Photonic crystal surface-emitting lasers on bulk silicon substrate

We report here heterogeneous photonic crystal (PC) bandedge surface emitting membrane lasers on bulk silicon (Si) substrates. Optically pumped lasers were demonstrated experimentally with single mode operation and side-mode suppression ratio (SMSR) greater than 13.5 dB. Thermal resistance was investigated to evaluate the heat dissipation and lasing characteristics afforded by this integration and potential for high efficiency application.

Printed photonic crystal membrane lasers on silicon

We report two types of photonic crystal membrane lasers on silicon based on photonic crystal membrane reflectors and photonic crystal bandedge effect. Multi-layer stacking and integration for beam routing and modulation will also be discussed for integrated photonics.