Majority Carrier Concentration and Minority Carrier Lifetime in Mid-wave Infrared InGaAs/InAsSb and InAs/InAsSb Superlattice nBn Detectors

Abstract

Infrared unipolar barrier detectors based on III-V materials have progressed tremendously due to success in improving material quality and bandgap engineering. In the standard nBn detector, the single unipolar barrier extends into the conduction band, blocking the majority carrier dark current and significantly inhibiting the generation-recombination and surface contributions to the dark current. The barrier serves to make the detector a minority carrier, diffusion-limited device, however doping still has a dominant impact on device performance due to its relationship with the minority carrier lifetime and minority carrier concentration. Increasing doping degrades the minority carrier lifetime, and thus the quantum efficiency of the photodetector. Diffusion dark current in the nBn detector, which is proportional to the minority carrier concentration, is initially reduced by increased doping until it begins to have an adverse effect on the minority carrier lifetime. Ultimately, absorber doping density significantly affects nBn photocollection and noise characteristics and must be precisely controlled to optimize photodetector performance. Recent advances leading to high minority carrier lifetime in strain balanced InGaAs/InAsSb superlattices have led to it being considered as a higher mobility drop-in replacement to the InAs/InAsSb superlattice nBn. Two InAs/InAsSb and three InGaAs/InAsSb nBn structures designed for maximum electron-hole wavefunction overlap with 5.1-5.3 um wavelength cutoffs have been grown with different absorber doping profiles by molecular beam epitaxy. The material is examined by time-resolved and steady-state photoluminescence, X-ray diffraction, and Nomarski surface imaging. The samples are then processed into variable-area mesa arrays using standard lithography and contact metal deposition. The devices are packaged in and wire-bonded to 68-pin leadless-chip carriers, which are then mounted in a vacuum-sealed dewar for temperature-controlled measurements of the photocurrent, dark current, and capacitancevoltage to evaluate the doping concentration profile in each device. The undoped Ga-free nBn’s exhibited the lowest background n-type majority carrier concentration of 6x10 “cm ~ with a minority carrier lifetime of 3 us. The undoped InGaAs/InAsSb superlattice exhibited a ~4« higher majority carrier concentration of 2x10 ~ cm™~ with a minority carrier lifetime of 2 us. Si-doped samples with constant and graded doping profiles are also examined, and the minority carrier lifetime is observed to degrade with increased doping. An analysis of the minority carrier lifetime’s dependance on doping, impact on detector performance and other characterization results will be presented. Approved for public release: Distribution is unlimited. AFMC PA number xxx-xxxx