Abstract
Arrays of pn junctions have been fabricated with n-Si microneedles. In situ doping vapor-liquid-solid (VLS) growth has been carried out with p-Si substrate having metallic catalyst (Au) dots on its surface, using Si2H6 and PH3 for supplying Si and phosphorus to fabricate n-Si microneedles on the surface of p-Si substrate in vertical direction; thus, pn junctions have been fabricated at microneedle-substrate interface. These n-Si microneedles have been grown at the temperature of 680 degrees C, which is about 420 degrees C less than the temperature (at least 1100 degrees C) required by conventional diffusion method of doping. In this work, n-Si microneedles have been successfully fabricated with 100% yield, the highest success ever for n-type VLS growth in micro range. The position and size of these n-Si microneedles are controllable. These n-Si microneedles are highly conductive. Physical and electrical characteristics of n-Si microneedles have been investigated by varying Au dot size and the level of phosphorus doping. The properties of interface pn junction have been investigated and compared with standard diode characteristics and theoretical results. Highly conductive n-Si microneedle arrays, embedded with interface pn junctions, might be used for collecting and processing bio-signals, profiling temperature/pressure inside living cells and many other sensor applications.