The hole mobility and carrier lifetime of [alpha] mercuric iodide high energy radiation detectors have been enhanced through crystal growth in microgravity. The improvement is closely correlated with specific characteristics of the crystal lattice, which have been identified by high resolution synchrotron x-ray diffraction imaging. These structural features can now be approached in terrestrial growth of [alpha] mercuric iodide.Gravity affects the uniformity of this crystal lattice in two distinct ways: 1) directly through deformation that it imposes on the lattice during growth and 2) indirectly through convection, which mixes residual impurities. The resulting inclusions harden the lattice and facilitate lattice folding. These changes modify in distinct ways the electronic parameters of detectors made from the crystals. As purification procedures are optimized, the formation of inclusions is curtailed, enhancing electronic properties in spite of lattice flexing through loss of precipitation hardening. With more than optimum purification, an array of inclusions is formed without measured deterioration in performance.These studies provide insight into those aspects of [alpha]-mercuric iodide crystal order associated with property improvement. As a consequence of the structural changes observed, requirements for starting material have been modified, physical vapor growth procedures have been adjusted, and crystal handling procedures have been changed to achieve superior radiation detectors. While the electronic properties of [alpha] mercuric iodide have thus already been improved, we provide evidence that further enhancement is possible.
Conference Dates: December 1, 1997
Conference Title: Materials Research Society Symposium
Pub Type: Conferences
crystal growth, mercuric iodide, microgravity