Thin Film Solid State Active Dosimetry

Abstract

With the many advances in semiconductor manufacturing, the pool of available materials for use in their production also continues to broaden. One such example is aluminum antimonide (AlSb). Its promising properties for radiation detection have attracted multiple researchers, and allow for the possibility that it may be a high resolution, room temperature x-ray/gamma detector. Antimony has an atomic number of 51 (Z=51) and is responsible for the majority of photon interactions. Furthermore, the mass attenuation coefficient is comparable with other well-known solid state gamma detectors such as CZT. With a band gap of 1.6 eV (CZT=1.5 eV), low leakage current at room temperature is expected, and high charge carrier statistics from radiation interactions can be expected. Charge carrier statistics are driven by high charge mobility (μ) and lifetime (τ). μτ for CZT is on the order of 5x10{sup -3} cm{sup 2}/V for electrons, but two orders of magnitude smaller for holes. This results in large variations in detector pulse height depending on the location of interaction (close to the anode vs. close to the cathode). Theoretically, AlSb should exhibit much more symmetric electron and hole properties near 5x10{sup -3} cm{sup 2}/V. According to the Hecht relation, this should produce a more uniform detector response and increase the number of generated charge carriers, improving resolution. An added benefit is that AlSb can be grown directly onto Si substrates, enabling fully integrated circuit board-level sensors. However, several characteristic properties remain unknown and inconsistent published results due to difficulties in producing the material. Difficulties in bulk growth methods (material interactions with growth hardware such as crystals and air) resulted in high levels of defects. The use of AlSb in optoelectronics from thin film growth methods has been documented, including growth directly onto Si, and provides the potential for much more controlled material. In our work we use thin film growth of AlSb geared towards high quality material for understanding the properties for radiation detection. (authors)