nBn extended short-wavelength infrared focal plane array

Area of Science:

• Semiconductor Physics
• Materials Science
• Infrared Technology

Background:

• Type-II superlattices (T2SLs) offer tunable bandgaps for infrared optoelectronics.
• The nBn photodetector architecture suppresses dark current via a large-bandgap electron barrier.
• Short-wavelength infrared (SWIR) imagers are crucial for various applications.

Purpose of the Study:

• To demonstrate an extended short-wavelength nBn InAs/GaSb/AlSb type-II superlattice-based infrared focal plane array imager.
• To introduce a novel superlattice design for the electron barrier and an etch-stop scheme for improved performance.
• To characterize the photodetector's performance, including cutoff wavelength, quantum efficiency, dark current, and specific detectivity.

Main Methods:

• Fabrication of an nBn photodetector using InAs/GaSb/AlSb type-II superlattices.
• Implementation of a new InAsSb/GaSb superlattice for the electron barrier.
• Development of a bi-layer etch-stop scheme for substrate removal and shorter wavelength cut-on.
• Characterization of device performance at varying temperatures (150 K and 300 K) and biases.

Main Results:

• Demonstrated cutoff wavelengths of ~2.30 µm (150 K) and ~2.48 µm (300 K).
• Achieved saturated quantum efficiencies of 59.7% (150 K) and 63.8% (300 K) without antireflection coating.
• Obtained low dark current densities: 8.75×10⁻⁸ A/cm² (150 K, -400 mV) and 4.75×10⁻² A/cm² (300 K, -200 mV).
• Recorded high specific detectivities: 2.82×10¹² cm·Hz¹/² /W (150 K, 1.78 µm) and 8.55×10⁹ cm·Hz¹/² /W (300 K, 1.78 µm).

Conclusions:

• The novel nBn photodetector architecture with an extended short-wavelength T2SL design significantly reduces dark current.
• The developed etch-stop scheme enables complete substrate removal and facilitates shorter wavelength operation.
• The demonstrated device performance, particularly high detectivity at room temperature, shows great promise for SWIR imaging applications.