Long-wave type-II superlattice detectors with unipolar electron and hole barriers

The performance of a long-wave infrared type-II InAs/GaSb superlattice photodetector with a 50% cutoff wavelength of approximately 8.7 μm is presented. The ability to lower dark current densities over traditional P-type-Intrinsic-N-type diodes is offered by way of hetero-structure engineering of a pBiBn structure utilizing superlattice p-type (p) and n-type (n) contacts, an intrinsic (i) superlattice active (absorber) region, and uni-polar superlattice electron and hole blocking (B) layers. The spectral response of this pBiBn detector structure was determined using a Fourier transform infrared spectrometer, and the quantum efficiency was determined using a 6250 nm narrow band filter and a 500 K blackbody source. A diode structure designed, grown, and fabricated in this study yielded a dark current density of 1.05 × 10 −5 A∕cm 2 at a reverse bias of −50 mV and a specific detectivity value of greater than 10 11 Jones at 77 K. Theoretical fittings of the diode dark currents at 77 K were used in this study to help isolate the contributing current components observed in the empirical dark current data. A variable temperature study (80 to 300 K) of the dark current is presented for a diode demonstrating diffusion-limited dark current down to 77 K. 1 Introduction Electro-optic and infrared (EO/IR) sensors are being developed and deployed for a wide variety of military systems applications that include but are not limited to special operation missions that call for situational awareness at a covert level. To meet the ever-increasing demands for next-generation imaging systems which include higher operating temperatures and reduced size, weight, and power, a number of technologies are readily deployed for the visible, shortwave infrared (SWIR), mid-wave infrared (MWIR), and long-wave infrared (LWIR) spectral bands. 1 These imaging systems maintain a diverse grouping of materials that excel in their individual categories, or more specifically, in their respective spectral bands where their properties make them ideal candidates. For example, InGaAs-based IR focal plane array (FPA) technologies are commonly used for SWIR sensors that operate in the 1.0 to 1.8 μm band, while InSb-based FPAs tend to dominate as MWIR sensors in the 3 to 5 μm band. 2 For the 8 to 14 μm LWIR band, sensor technologies include Hg 1−x Cd x Te (MCT), microbolometers, and Type-II superlattices (SLS).