Current helium-3 tube based thermal neutron detectors have shortcomings in achieving simultaneously high efficiency and low voltage while maintaining adequate fieldability performance. By using a three-dimensional silicon p-i-n diode pillar array filled with boron-10 these constraints can be overcome. The fabricated pillar structured detector reported here is composed of 2μm diameter silicon pillars with a 4μm pitch and height of 12μm. A thermal neutron detection efficiency of 7.3+∕−0.6% and a neutron-to-gamma discrimination of 105 at 2V reverse bias were measured for this detector. When scaled to larger aspect ratio, a high efficiency device is possible.
A recently proposed micropillar semiconductor platform filled with a high volume of isotopic b10oron (B10) has great potential to yield efficient thermal neutron detectors because B10 has a high thermal neutron cross section. Here, the authors report the development of conformal filling of high aspect ratio silicon micropillar platforms with B10 by low pressure chemical vapor deposition (LPCVD) using B10-enriched decaborane (B10H14). The relationships between the pillar structure and the key process parameters including reaction temperature, process pressure, and buffer gas flow rates were investigated to optimize the conformal filling on these structures. Reaction temperature of 420–530 °C, process pressure of 50–450 mTorr, 0.3 SCCM (SCCM denotes cubic centimeter per minute at STP) B10H14 flow rate, and argon buffer gas flow rate of 0–200 SCCM were used to deposit B10 materials into the micropillar structures with aspect ratios of 3:1, 6:1, and 10:1. All three mentioned pillar structures were found to be completely (∼100%) filled with B10 at 420 °C and 50 mTorr. At higher process temperatures, the fill factors of the three pillar structures decreased significantly. The effect of reaction temperature, process pressure, and buffer gas flow rates on the LPCVD deposition mechanism with respect to the structure geometry are also discussed.
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