Examining Thin Film AlSb for Room Temperature Gamma Detectors

A thin film semiconductor device was grown by MBE methods, characterized for material quality and evaluated for suitability as a room temperature gamma radiation detector. The objective was to produce a device that was superior to current semiconductor detectors, namely HPGe and CZT which have different limitations due to intrinsic material characteristics. AlSb was chosen because of its desirable properties which include the high atomic number of antimony (Z = 51), relatively large band gap (Eg = 1.6 eV), and theorized high dual carrier mobility. Simulations were performed using MCNP5 to predict energy deposited in AlSb by low energy gammas from Ba-133 and Co-57. A benchmark model was developed using a silicon surface barrier detector to validate AlSb simulations. Prior to radiation experiments, a series of characterization methods were employed to evaluate the material quality. Surface features were measured by Nomarski imaging and AFM, revealing an orange peel texture and screw dislocations. The material composition was examined using XRD and the AlSb layer was observed to be fairly narrow along the lattice axis indicating reduced strain on the lattice structure. Electrical measurements were conducted which exposed low values for resistivity (ρ = 10-3 \u03a9-cm) and average carrier mobility (~ 100 cm2/Vs), and a high hole concentration (~ 1019 cm-3). I-V curves indicated a leaky nature for the diode, and it is suspected that Zener breakdown was occurring. During radiation experiments, no signal was observable above noise levels. The high hole concentration may have contributed to this result by eliminating the intended intrinsic region between the electrodes. Further studies should be conducted with AlSb to investigate the effects of compensation doping and/or growth temperature on carrier concentration and AlSb purity