Monolithic lateral p-n junction GaAs nanowire diodes via selective lateral epitaxy.

Semiconductor p-n junctions are essential building blocks of electronic and optoelectronic devices. Although vertical p-n junction structures can be formed readily by growing in sequence, lateral p-n junctions normal to surface direction can only be formed on specially patterned substrates or by post-growth implantation of one type of dopant while protecting the oppositely doped side. In this study, we report the monolithic formation of lateral p-n junctions in GaAs nanowires (NWs) on a planar substrate sequentially through the Au-assisted vapor-liquid-solid selective lateral epitaxy using metalorganic chemical vapor deposition. p-type and n-type segments are formed by modulating the gas phase flow of p-type (diethylzinc) and n-type (disilane) precursorsin situduring nanowire growth, allowing independent sequential control of p- and n-doping levels self-aligned in-plane in a single growth run. The p-n junctions formed are electrically characterized by fabricating arrays of p-n junction NW diodes with coplanar ohmic metal contacts and two-terminalI-Vmeasurements. The lateral p-n diode exhibits a 2.15 ideality factor and a rectification ratio of ∼106. The electron beam-induced current measurement confirms the junction position. The extracted minority carrier diffusion length is much higher compared to those previously reported, suggesting a low surface recombination velocity in these lateral NWp-n diodes.

Elastocapillary Force Induced Alignment of Large Area Planar Nanowires.

Achieving large scale precise positioning of the vapor-liquid-solid (VLS) nanowires is one of the biggest challenges for mass production of nanowire-based devices. Although there have been many noteworthy progresses in postgrowth nanowire alignment method development over the past few decades, these methods are mostly suitable for low density applications only. For high density applications such as transistors, both high yield and density are required. Here, we report an elastocapillary force-induced nanowire-aligning method that is extremely simple, clean, and can achieve single/multiple nanowire arrays with up to 98.8% yield and submicron pitch between the nanowires.

High Aspect Ratio ß-Ga2O3 Fin Arrays with Low-Interface Charge Density by Inverse Metal-Assisted Chemical Etching.

ß-Ga2O3, with a bandgap of ∼4.6-4.9 eV and readily available bulk substrates, has attracted tremendous interest in the wide bandgap semiconductor community. Producing high aspect ratio ß-Ga2O3 3D nanostructures without surface damage is crucial for next-generation power electronics. However, most wet etching methods can only achieve very limited aspect ratios, while dry etch usually damages the surface due to high energy ions. In this work, we demonstrate the formation of ß-Ga2O3 fin arrays on a (010) ß-Ga2O3 substrate by metal-assisted chemical etching (MacEtch) with high aspect ratio and sidewall surfaces with excellent quality. The etching was found to be strongly crystal orientation dependent, and three kinds of vertical structures were formed after MacEtch. The Schottky barrier height (SBH) between Pt and various MacEtch-produced ß-Ga2O3 surfaces and sidewalls was found to decrease as the aspect ratio of the ß-Ga2O3 vertical structure increased. This could be attributed to the different amount of oxygen lost at the surface after etching, as indicated by the XPS and TEM examination. Very little hysteresis was observed in the capacitance-voltage characteristics for the 3D Pt/Al2O3/ß-Ga2O3 MOS capacitor structures, and the extracted interface trap density was as small as 2.73 × 1011 cm-2 eV-1, comparable to or lower than that for unetched planar ß-Ga2O3 surfaces.