Ajit V. Barve

High operating temperature interband cascade midwave infrared detector based on type-II InAs/GaSb strained layer superlattice

We report on an interband cascade mid-wave infrared (MWIR) detector based on type-II InAs/GaSb/AlSb strained layer superlattices (T2SL). The reported device has a seven-stage cascade region, each segment containing a MWIR absorber region, a graded T2SL transport region, and an interband tunneling region. Above room temperature spectral response was observed, with a cutoff wavelength of 7 μm at 420 K. Detailed radiometric measurements yielded a Johnson noise limited detectivity of 3.0 × 1011 cmHz1/2W−1 (8.9 × 108 cmHz1/2W−1) and a dark current density of 3.6 × 10−7 A/cm−2 (7.3 × 10−3 A/cm−2) near zero bias with a 100% cutoff wavelength of 5.2 μm and 6.2 μm at 77 K (295 K), respectively, with an estimated 36.2% QE.

Multi-stack InAs/InGaAs sub-monolayer quantum dots infrared photodetectors

We report on the design and performance of multi-stack InAs/InGaAs sub-monolayer (SML) quantum dots (QD) based infrared photodetectors (SML-QDIP). SML-QDIPs are grown with the number of stacks varied from 2 to 6. From detailed radiometric characterization, it is determined that the sample with 4 SML stacks has the best performance. The s-to-p (s/p) polarized spectral response ratio of this device is measured to be 21.7%, which is significantly higher than conventional Stranski-Krastanov quantum dots (∼13%) and quantum wells (∼2.8%). This result makes the SML-QDIP an attractive candidate in applications that require normal incidence.

Reduction in dark current using resonant tunneling barriers in quantum dots-in-a-well long wavelength infrared photodetector

We report the use of resonant tunneling (RT) assisted barriers to reduce the dark current in quantum dots-in-a-well (DWELL) infrared photodetectors. Designed RT barriers allow energy-selective extraction of photoexcited carriers while blocking a continuum of energies. Over two orders of magnitude reduction in the dark current in the RT-DWELL device over a control sample without RT-DWELL at 77K has been demonstrated. Specific detectivity (D*) of 3.6×109cmHz1∕2W−1 at 77K at λpeak=11μm with a conversion efficiency of 5.3% was obtained in the RT-DWELL device. D* for the RT-DWELL device is five times higher than that of the control sample.

Systematic study of different transitions in high operating temperature quantum dots in a well photodetectors

We report a systematic study of different transitions in quantum dots-in-a-well infrared photodetectors in order to optimize the signal to noise ratio of the detector. Bound to continuum transitions offer very high extraction probability for photoexcited electrons but poor absorption coefficient, while the bound to bound transitions have higher absorption but poorer extraction probability. Bound to quasibound transitions are optimum for intermediate values of electric fields with superior signal to noise ratio. The bound to quasibound device has the detectivity of 4×1011 cm Hz1/2 W−1 (3V, f/2 system) at 77 K and 7.4×108 cm Hz1/2 W−1 at 200 K, which is highest reported detectivity at 200 K for detector with long wave cutoff wavelength.

Barrier Engineered Infrared Photodetectors Based on Type-II InAs/GaSb Strained Layer Superlattices

We present the design, growth, fabrication, and characterization of unipolar barrier photodiodes, pBiBn, based on type-II InAs/GaSb superlattice for midwave and longwave infrared detection. Design optimization of barriers using bandgap and band-offset tailorability of InAs/GaSb/AlSb superlattice system, their advantages and evolution of heterostructure designs are discussed for both the regimes. Dark current densities of 1.6 × 10^-7 and 1.42 × 10^-5 A/cm² are measured at 77 K for midwave and longwave detectors with cutoff wavelengths of 5 and 10 μm, respectively. Responsivities of 1.3 (QE = 38%) and 1.66 A/W (QE = 23.5%) are measured at 4.2 and 8.7 μm for the midwave and longwave, respectively, at 77 K. Shot noise limited peak detectivity of 8.9 × 10¹² and 7.7×10¹¹ cm-Hz^1/2-W^-1 are observed at -10 and -40 mV for midwave infrared and longwave infrared detectors, respectively, at 77 K.

Resonant Tunneling Barriers in Quantum Dots-in-a-Well Infrared Photodetectors

The use of resonant tunneling (RT) barriers in the design of quantum dots-in-a-well (DWELL) infrared photodetectors is reported. The design of RT barriers for a variety of goals has been discussed. For simple DWELL designs, we demonstrate 2-3 orders-of-magnitude reduction in the dark current, with significant increase in the specific detectivity (D *) of the device. Two RT barriers are designed to selectively extract midwave and longwave components of the spectral response. We also report the use of RT barriers on strain-optimized quantum dots-in-a-double-well (DDWELL) structures to achieve very low dark current levels with peak D * of 2.9 ×1010 cm· Hz1/2 /W for a longwave infrared detection. Ability to select a particular wavelength in the spectral response is demonstrated with DDWELL architectures as well.

Quantum Dots-in-a-Well Focal Plane Arrays

In this paper, the basics and some of the recent developments in quantum dots-in-a-well (DWELL) focal plane arrays (FPAs) are reviewed. Fundamentally, these detectors represent a hybrid between a conventional quantum well infrared photodetector (QWIP) and a quantum dot infrared photodetector (QDIP), in which the active region consists of quantum dots (QDs) embedded in a quantum well (QW). This hybridization grants DWELLs many of the advantages of its components. These advantages include normally incident photon sensitivity without gratings or optocoupers, like QDIPs, and reproducible control over operating wavelength through ldquodial-in recipesrdquo as seen in QWIPs. Recently reported high-temperature operation results for DWELL FPAs now back up the conclusions drawn by the long carrier lifetimes observed in DWELL heterostructures using femtosecond spectroscopy. This paper will conclude with a preview of some upcoming advances in the field of DWELL FPAs.

Sub-monolayer quantum dots in confinement enhanced dots-in-a-well heterostructure

We have investigated optical properties and device performance of sub-monolayer quantum dots infrared photodetector with confinement enhancing (CE) barrier and compared with conventional Stranski-Krastanov quantum dots with a similar design. This quantum dots-in-a-well structure with CE barrier enables higher quantum confinement and increased absorption efficiency due to stronger overlap of wavefunctions between the ground state and the excited state. Normal incidence photoresponse peak is obtained at 7.5 μm with a detectivity of 1.2 × 1011 cm Hz1/2 W−1 and responsivity of 0.5 A/W (77 K, 0.4 V, f/2 optics). Using photoluminescence and spectral response measurements, the bandstructure of the samples were deduced semi-empirically.

Three color infrared detector using InAs/GaSb superlattices with unipolar barriers

We report on a three color heterojunction band gap engineered type-II InAs/GaSb strained-layer superlattice photodiode for short-wave infrared (SWIR), mid-wave infrared (MWIR), and long-wave infrared (LWIR) detection. The reported structure is a three contact device with nBn architecture for SWIR and MWIR and heterojunction PIbN architecture for LWIR detection. At 77 K, the cutoff wavelength for SWIR, MWIR, and LWIR regions are 3.0 μm, 4.7 μm, and 10.1 μm, respectively. The reported architecture can be used for simultaneous detection in the LWIR/MWIR and LWIR/SWIR bands as well as sequential detection in the MWIR/SWIR bands by switching the polarity of the applied bias.

Investigation of multistack InAs/InGaAs/GaAs self-assembled quantum dots-in-double-well structures for infrared detectors

The authors report the InAs/InGaAs/GaAs/AlGaAs quantum dots-in-double-well (D-DWELL) design, which has a lower strain per DWELL stack than the InAs/InGaAs/GaAs DWELLs thereby enabling the growth of many more stacks in the detector. The purpose of this study is to examine the effects of varying the number of stacks in the double DWELL detector on its device performance. The structures are grown by solid source molecular beam epitaxy on GaAs substrates. After fabrication of single pixel devices, a series of device measurements such as spectral response, dark current, total current, and responsivity were undertaken and the photoconductive gain and the activation energies were extracted. The goal of these experiments is not only to optimize the device performance by optimizing the number of stacks but also to investigate the transport properties as a function of the number of stacks.