Nanocrystalline Si-Based Resistive Humidity Sensors Prepared via HWCVD at Various Filament Temperatures
The growth of nanocrystalline Si on glass substrates via hot-wire chemical vapor deposition (HWCVD) at various filament temperatures and the fabrication of nanocrystalline Si-based resistive humidity sensors are reported. Experimental results indicate that the average diameter of nanocrystalline Si particles increases with increasing filament temperature. Measurements of the resistivity change of samples with humidity at 25°C show that the sensor response of samples fabricated at high filament temperatures is lower than that of samples fabricated at low filament temperatures. The sensitivity of the sensor increases with relative humidity.
Micro Humidity Sensor Based on a GaN Chip With Silica Opal
The fabrication of a micro humidity sensor based on a GaN chip with silica opal is reported. The GaN chip containing InGaN/GaN multi-quantum well provides the two key functions of light emission and detection and the emitted light can be directly coupled into and out of the humidity-sensitive opal through the transparent sapphire substrate. The novel chip-scale integration scheme fully eliminates the complex assembly of external optical elements. The measured photocurrent signal quantitatively reflects the humidity change and has a linear relation of 0.24 $\mu \text{A}$ /% over a wide humidity range of 10-90 %. The developed micro-sensor possesses the advantages of compact size, low cost, high repeatability, and ease of integration and operation, which paves the way for its widespread adoption in humidity sensing.
Mass spectrometry detection of radicals in SiH4-CH4-H2 glow discharge plasmas
After reviewing the various in situ and non-intrusive diagnostics of radicals in low-pressure discharges, we present the technique of threshold ionization mass spectrometry. This technique has been applied to measure SiHn, CHn (n<or=3) and H radical densities in radio frequency (RF) capacitively coupled parallel plate discharges of silane, methane and hydrogen. The procedure of determination of absolute radical densities is detailed. The comparison of SiH3 and CH3 densities near the wall reveals large differences in surface reaction probabilities. Then, the contribution of SiHn and CHn (n<or=3) flux to a-Si:H and a-C:H deposition is investigated and compared with the growth rate. Finally, for the first time, we report a measurement of H atom density by mass spectrometry in a hydrogen discharge.