High-performance heterostructure backward diode detectors

The combination of atmospheric propagation windows and notches, in conjunction with the rich spectral signatures of many materials in the millimeter-wave through THz region of the electromagnetic spectrum, make sensing and imaging in this spectral range of particular interest in security, defense, and medical spheres. For sensing and imaging systems, high-sensitivity and low-noise detectors are key components; micro- and nano-scale devices are especially promising for detectors since small device scales naturally lead to lower device capacitances (and thus increased operational frequency) while the exploitation of quantum mechanical tunneling at the nanoscale offers significant potential for improving intrinsic detector performance. We report recent developments in InAs/AlSb/GaSb heterostructure backward tunnel diodes for millimeter-wave through THz detection and imaging applications. These devices have demonstrated measured room-temperature curvatures of 47 V-1, exceeding the fundamental limitation of q/kT=38.5 V-1 for Schottky diodes. Since detector sensitivity is proportional to curvature, these increases in curvature translate to improved sensitivity; unmatched sensitivities of 4600 V/W at 94 GHz have been measured, and sensitivities of nearly 50,000 V/W are projected under conjugately-matched conditions. These devices also offer extremely low noise performance; we report projected NEP values below 0.2 pW/Hz1/2 at 94 GHz for conjugately-matched detectors. A challenging issue in the design of optimized interband tunneling-based devices is the difficulty in accurately simulating and modeling the devices. We have developed a numerical model based on self-consistent solution of the Poisson/Schrodinger equations coupled with 8-band k•p band structure and transfer-matrix calculations that agrees well with experimental device results and enables projection of performance for novel structures. This simulation framework suggests several promising avenues for further device performance improvement, and provides a means to optimize detector performance for applications.