In recent years when the demand for high-performance biosensors has been aroused, a field-effect transistor (FET)-type biosensor (BioFET) has attracted great interest because of its high sensitivity, label-free detection, fast detection speed, and miniaturization. However, the insulating membrane in the conventional BioFET, which is essential in preventing the surface dangling bonds of typical semiconductors from nonspecific bindings, has limited the sensitivity of biosensors. Here, we present a highly sensitive and reusable membraneless BioFET based on a defect-free van der Waals material, tungsten diselenide (WSe). We intentionally generated a few surface defects that serve as extra binding sites for the bioreceptor immobilization through weak oxygen plasma treatment, consequently magnifying the sensitivity values to 2.87 × 10 A/A for 10 mM glucose. The WSe BioFET also maintained its high sensitivity even after several cycles of rinsing and glucose application were repeated.

GaAs solar cells with nanostructured emitter layers were fabricated via metal-assisted chemical etching. Au nanoparticles produced via thermal treatment of Au thin films were used as etch catalysts to texture an emitter surface with nanohole structures. Epi-wafers with emitter layers 0.5, 1.0, and 1.5 um in thickness were directly textured and a window layer removal process was performed before metal catalyst deposition. A nanohole-textured emitter layer provides effective light trapping capabilities, reducing the surface reflection of a textured solar cell by 11.0%. However, because the nanostructures have high surface area to volume ratios and large numbers of defects, various photovoltaic properties were diminished by high recombination losses. Thus, we have studied the application of nanohole structures to GaAs emitter solar cells and investigated the cells' antireflection and photovoltaic properties as a function of the nanohole structure and emitter thickness. Due to decreased surface reflection and improved shunt resistance, the solar cell efficiency increased from 4.25% for non-textured solar cells to 7.15% for solar cells textured for 5 min.

Heavily tellurium (Te)-doped GaAs layers with diethyltellurium (DETe) grown by metalorganic chemical vapor deposition (MOCVD) were investigated. The existence of Te-rich microprecipitates might degrade both the electrical and optical properties. Compared to Si doping, the tunnel junction diode doped with Te doping revealed lower tunneling resistance. A comparative study using both Si and Te doping in the GaAs tunnel junction of GaInP/GaAs tandem solar cells showed a higher efficiency for Te doping. Therefore, the GaAs tunnel junction with Te doping can be considered to improve the device performance of GaAs-based multi-junction solar cells.

We proposed a new scheme, controlling the crack formation by notch patterns, to fabricate self-isolated high-efficiency gallium arsenide (GaAs)-based solar cells on a silicon (Si) substrate. The notch patterns introduced into the Si substrate were found to successfully generate the crack-free areas of 2 mm × 2 mm size separated by the cracks for the 5.8-μm-thick GaAs layers on it. The individual solar cells on the crack-free areas were confirmed to be electrically isolated from one another by the well-defined crack array. The open-circuit voltage and the efficiency of the crack-free cell were improved to 0.87 V and 18.0%, respectively, from 0.78 V and 14.7% for the cell with 33.2 cm −1 of linear crack density.Index Terms-Crack, gallium arsenide (GaAs), isolation, metalorganic chemical vapor deposition, photovoltaic cells, III-V semiconductor materials, silicon (Si).

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