Hexagonal boron nitride (hBN) growth was carried out on (111) Si substrates at a temperature of 1350 C using a cold wall chemical vapor deposition system. The hBN phase of the deposited films was identified by the characteristic Raman peak at 1370 cm À1 with a full width at half maximum of 25 cm À1 , corresponding to the in-plane stretch of B and N atoms. Chemical bonding states and composition of the hBN films were analyzed by X-ray photoelectron spectroscopy; the extracted B/ N ratio was 1.03:1, which is 1:1 within the experimental error. The fabricated metal-hBN-metal devices demonstrate a strong deep UV (DUV) response. Further, the hBN growth on the vertical (111) surfaces of parallel trenches fabricated in (110) Si was explored to achieve a thermal neutron detector. These results demonstrate that hBN-based detectors represent a promising approach towards the development of DUV photodetectors and efficient solid-state thermal neutron detectors.
Keywords chemical vapor deposition, hexagonal boron nitride, sapphire nitridation, growth temperature This paper reports on the epitaxial growth of hexagonal boron nitride (hBN) films on sapphire substrates in a cold wall chemical vapor deposition (CVD) system where different sapphire nitridation and hBN growth temperatures were employed. A thin and amorphous nitridated layer was formed at a low temperature (850 o C), which enabled subsequent epitaxial hBN growth at 1350 o C. The influences of the sapphire nitridation temperature and the growth temperature on the film quality were analyzed by X-ray diffraction (XRD) measurements.Higher than optimum nitridation and growth temperatures improve the crystalline quality of the nitridated layer, but does not favor the epitaxial growth of hBN. hBN films grown at the optimum conditions exhibit the c-lattice constant of 6.66 Å from the XRD θ-2θ scan, and the characteristic in plane stretching vibration at 1370.5 cm -1 from Raman spectroscopy. X-ray photoelectron spectroscopy analysis confirmed the formation of stoichiometric hBN films with excellent uniformity.
This paper reports on the device processing and characterization of hexagonal boron nitride (hBN) based solid-state thermal neutron detectors, where hBN thickness varied from 2.5 to 15 µm. These natural hBN epilayers (with 19.9% 10 B) were grown by a low pressure chemical vapor deposition process. Complete dry processing was adopted for the fabrication of these metal-semiconductor-metal (MSM) configuration detectors. These detectors showed intrinsic thermal neutron detection efficiency values of 0.86%, 2.4%, 3.15%, and 4.71% for natural hBN thickness values of 2.5, 7.5, 10, and 15 µm, respectively. Measured efficiencies are very close (≥ 92%) to the theoretical maximum efficiencies for corresponding hBN thickness values for these detectors. This clearly shows the hBN thickness scalability of these detectors. A 15 µm thick hBN based MSM detector is expected to yield an efficiency of 21.4%, if enriched hBN (with ~100% 10 B) is used instead of natural hBN. These results demonstrate that the fabrication of hBN thickness scalable highly efficient thermal neutron detectors is possible.High efficiency neutron detectors are essential for homeland security and nuclear safeguards, since neutrons are a very specific indicator of special nuclear materials (SNMs). Development of solid-state neutron detectors (SSNDs) represents an emerging area of research, because the existing highest efficiency 3 He gas based neutron detectors have drawbacks such as high cost, bulky nature, and high pressure and high bias voltage requirement [1][2][3]. SSNDs utilize high thermal neutron capture cross section (σ) values of neutron sensitive isotopes such as 10 B (σ = 3840 barns) and 6 Li (σ = 940 barns) [2]. Most SSNDs are microstructured Si filled with 10 B or 6 Li, and are of heterogeneous type with separate neutron conversion and charge collection regions.10 B has a natural abundance of ~19.9% [2] and is a constituent element of hexagonal boron nitride (hBN). hBN is therefore an excellent material for homogenous SSND fabrication, where both neutron conversion and charge collection can occur in this semiconductor. Large bandgap of hBN (5.5 eV to 6 eV [4-6]) makes hBN SSNDs radiation hardened. hBN SSNDs are also relatively insensitive to gamma rays [7]. The theoretical requirement of hBN thickness (assuming 100% 10 B) is 35 m and 80 µm, for the detection efficiency of 50% and 80%, respectively, as indicated by our simulation [7]. This work reports on the growth of thick hBN of thickness ranging from 2.5 to 15 m using a chemical vapor deposition (CVD) process. SSNDs with metal-semiconductor-metal (MSM) configuration were fabricated with these hBN films. Charge transport in these devices is along a-axis, which represents the highest charge carrier mobility path in hBN [8]. Device capacitance (Cdev) and dark current (Idev) of an hBN MSM SSND are orders of magnitude lower compared to microstructured Si based SSNDs [3,9]. Since lower values of Cdev and Idev allow for scaling to larger device areas, hBN MSM SSNDs can be scaled to much larger de...
This paper reports on the use of 10 B nano/microparticles in order to fill microstructures of deep trenches fabricated in n-type Si (110) bulk wafers for the development of solid-state thermal neutron detectors. The high aspect-ratio trenches were fabricated in the wafer by wet etching, with a trench width of 3.5 to 6 lm and a maximum depth of 120 lm. Boron was diffused at a temperature of $1000 C in order to convert the entirety of the delicate Si microstructures into a p þ -n junction diode. The deep trenches of the diode were completely filled with 10 B nanoparticles using a simple room-temperature process involving the pumping and venting of a vacuum chamber containing the etched wafer with 10 B nanoparticles atop. The simple filling process was reproduced consistently, and the best 2.5 Â 2.5 mm 2 device demonstrated an intrinsic thermal neutron (E n < 0.5 eV) detection efficiency of 32.2 6 1.5% under a self-biased condition. This result is promising as it demonstrates a complete, low-cost fabrication process for the development of efficient thermal neutron detectors.Published by AIP Publishing. [http://dx.
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