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Barrier engineering for high-performance nBn infrared photodetectors

Uzgur, Fatih
Despite intensive studies, for high-performance applications, lowering dark current is still a challenging problem for pn-type infrared (IR) photodetectors. Over the last two decades, barrier-type IR detectors have been proposed as a solution for obtaining high-performance and high operation temperature conditions. However, the valence band discontinuity limits the material alternatives to which the barrier detector architecture can be applied. In this thesis work, it has been numerically shown that some material limitations in the barrier detector architecture can be eliminated using bandgap engineering techniques. Herein, simulations and analyses were performed by using Synopsys Sentaurus technology computer-aided design (TCAD) commercial device simulator via calculations of the current, continuity, and Poisson’s equations with high precision. In this study, delta-doped layers, together with compositionally grading, were utilized to get InGaAs and HgCdTe nBn type IR barrier detector configurations. For the shortwave IR (SWIR) band InGaAs nBn detector, lattice-matched InAlAs and lattice-mismatched InGaAs were used for the barrier material. At least 40 and 20 times improvement, respectively, were calculated in the dark current level by suppressing the surface leakage and generation-recombination (G-R) current mechanisms without compromising any photo-response when compared to the conventional pn junction. This method was also applied successfully for obtaining an extended SWIR (eSWIR)/SWIR InGaAs dual-band nBn detector structure. In the case of HgCdTe material systems, strong suppression of G-R and trap assisted tunneling (TAT) currents were numerically demonstrated with the designed nBn structures in the SWIR, midwave IR (MWIR), and longwave IR (LWIR) bands, which could be useful for the alternative substrate HgCdTe technology. The HgCdTe dual-band nBn detector configuration was also examined in MWIR/LWIR bands again by using compositionally graded and delta-doped layers. Thanks to the flexibility of this method, the length and thickness of the barrier can be adjusted, while zero valence band offset is achieved at the same time for the compositionally bandgap adjustable materials.