Yüksek performanslı nBn kızılötesi fotodedektörler için bariyer mühendisliği.

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.Thesis (Ph.D.) -- Graduate School of Natural and Applied Sciences. Micro and Nanotechnology

A Dual-Band HgCdTe nBn Infrared Detector Design

Low dark current and/or high operating temperature are the main motivations behind the nBn detector structures where removing the valence band discontinuity is usually an important design challenge. With the utilization of the bias polarity, these structures can also be easily designed as dual-band detectors and in this study, a dual-band (MWIR / LWIR) HgCdTe nBn detector configuration has been numerically examined. Valence band barrier suppression has been obtained with the delta-doped and compositional graded layers similar to the recent single band studies

InGaAs nBn SWIR detector design with lattice-matched InAlGaAs barrier

Dark current optimization with band gap engineering has been numerically studied for InGaAs nBn type infrared photodetectors. Undoped InAlGaAs grading layers are utilized in constructing the barrier and dipole delta-doped layers are placed in both sides of the graded layers for eliminating valence band offset. As a result, the high band gap barrier layer blocks the majority carriers and allows minority carrier flow while minimizing various dark current components, as expected from an nBn detector. Substantial improvement has been shown in the dark current level without compromising any photoresponse compared to the conventional pn junction and recently proposed all InGaAs nBn type photodetectors

Barrier engineering for HgCdTe unipolar detectors on alternative substrates

Delta-doped layers together with compositionally grading have been utilized to get nBn configurations for the HgCdTe material system in all the short-wave (SWIR), medium-wave (MWIR) and long-wave (LWIR) infrared bands. Shockley Read Hall (SRH), trap-assisted tunneling (TAT), Auger and radiative recombination mechanisms have been included in the analyses and strong suppression of SRH and TAT currents have been demonstrated with the designed structures. This methodology is especially useful when the carrier lifetime is limited due to alternative substrate usage. No degradation in photo-response has been observed as adjusting the valence band offset is quite flexible with the delta-doped nano-layers and the valence band barrier can be completely removed. Calculations have been performed for 1-3 mu s lifetime targeting the alternative substrate applications and up to 60 degrees of increase in the operation has been shown to be possible

All InGaAs Unipolar Barrier Infrared Detectors

Unipolar barrier detector design is a challenge for InGaAs material system since there is a lack of proper barrier material that blocks majority carriers and allows unimpeded flow of minority carriers. As a bandgap engineering solution, Al/Sb free all InGaAs unipolar barrier detectors have been numerically designed here by compositionally graded and delta-doped layers. Comparison with conventional heterojunction detectors results that there is at least one order of magnitude improvement in dark current without compromising any photoresponse performance. Detailed simulation characterization studies including sensitivity analysis with respect to the design parameters verify the robustness of the proposed structure

Al/Sb Free InGaAs Unipolar Barrier Infrared Detectors

It is numerically shown that Al/Sb free InGaAs unipolar barrier detectors with superior performance compared to the conventional heterojunction detectors can be constructed. Compositionally graded layers provide the transition between the high bandgap InGaAs barrier and the lattice matched InGaAs absorber layers. In addition, the delta doped layers remove the valence band offset in order to block only majority carriers and allow unimpeded flow of minority carriers. More than one order of magnitude reduction in the dark current is observed while photocurrent remains nearly unchanged. Proposed barrier structure utilized in this study is not limited to short wave infrared (SWIR) and can be applied to a variety of materials operating in various infrared regions