The heteroisomeric diode

Abstract

We have fabricated a new class of diode from two different polytypes of boron carbide. Diodes were fabricated by chemical vapour deposition from two different isomers of closo-dicarbadodecaborane: closo-1,2-dicarbadodecaborane (orthocarborane, C 2 B 10 H 12) and closo-1,7-dicarbadodecaborane (metacarborane, C 2 B 10 H 12), differing only by the carbon placement within the icosahedral cage. We find that the electronic structure (molecular orbitals) of these two isomer molecules and the resulting decomposition reflect the tendency of metacarborane to form an n-type semiconductor while orthocarborane is an effective source compound for a slightly p-type semiconducting boron carbide. The diodes of this novel class are effective solid state neutron detectors, and have a number of unique applications.

Neutron detection with cryogenics and semiconductors

“…They exposed the device to a nuclear reactor, acquired pulse-height spectra, and ascribed features in the spectra to the reaction products of the 10 B(n, α) 7 Li reaction. In subsequent work [17], they report the fabrication of an all-boron-carbide device made by depositing n-type boron carbide onto a p-type boron carbide layer previously deposited on an aluminium substrate, and, on exposure to a 120 n/cm 2 /s thermal neutron flux, they observed a current of approximately 18 fA. Unfortunately, the authors give no indication that this current is consistent with the incident flux, nor any explanation of how they observe such small currents in the presence of reported DC bias currents several orders of magnitude larger.…”

The all boron carbide diode neutron detector: Comparison with theory

“…Semiconducting boron carbide represents a new class of semiconducting materials with potential applications in neutron detection and radioactive decay calorimetry [1][2][3][4][5][6][7]. Boron carbide thin fi lm diodes and devices have begun to attract attention as potentially highly effi cient solid state neutron detectors [8][9][10].…”

“…This controversy has been somewhat addressed by the fabrication of all boron carbide neutron detectors [4,6] from semiconducting polytypes of boron carbide.…”

“…The homojunction diode has seen effective realization by doping the semiconducting boron carbide during fi lm growth through plasma-enhanced chemical vapor deposition (PECVD) from a suitable carborane [25,26]. A few all boron carbide devices [4,6], generally from semiconducting boron carbides formed from the decomposition of molecular precursors such as from the decomposition of closo-dicarbadodecaboranes: closo-1,2-dicarbadodecaborane (orthocarborane, C 2 B 10 H 12 ) and closo-1,7-dicarbadodecaborane (metacarborane, C 2 B 10 H 12 ) [4]. This latter all boron carbide device has been described as a heteroisomeric diode [4], as two electronically different semiconducting boron carbide polytypes are used, and the diode is not quite a conventional homojunction diode, although the two semiconducting boron carbides are compositionally similar.…”

“…A few all boron carbide devices [4,6], generally from semiconducting boron carbides formed from the decomposition of molecular precursors such as from the decomposition of closo-dicarbadodecaboranes: closo-1,2-dicarbadodecaborane (orthocarborane, C 2 B 10 H 12 ) and closo-1,7-dicarbadodecaborane (metacarborane, C 2 B 10 H 12 ) [4]. This latter all boron carbide device has been described as a heteroisomeric diode [4], as two electronically different semiconducting boron carbide polytypes are used, and the diode is not quite a conventional homojunction diode, although the two semiconducting boron carbides are compositionally similar. More recently, an all boron carbide heterojunction diode has been fabricated using two very different types of boron carbide [27].…”