| 1. |
- Hoglund, L, et al.
(author)
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Selective optical doping to predict the performance and reveal the origin of photocurrent peaks in quantum dots-in-a-well infrared photodetectors
- 2009
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In: INFRARED PHYSICS and TECHNOLOGY. - Exeter : Elsevier BV. - 1350-4495 .- 1879-0275. ; 52:6, s. 272-275
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Journal article (peer-reviewed)abstract
- Resonant optical pumping across the band gap was used as artificial doping in InAs/In0.15Ga0.85As/GaAs quantum dots-in-a-well infrared photodetectors. Through efficient filling of the quantum dot energy levels by simultaneous optical pumping into the ground states and the excited states of the quantum dots, the response was increased by a factor of 10. Low temperature photocurrent peaks observed at 120 and 148 meV were identified as intersubband transitions emanating from the quantum dot ground state and the quantum dot excited state, respectively by a selective increase of the electron population in the different quantum dot energy levels.
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| 2. |
- Höglund, Linda, 1974-, et al.
(author)
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Bias and temperature dependence of the escape processes in quantum dots-in-a-well infrared photodetectors
- 2008
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In: Applied Physics Letters. - New York : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 93:10, s. 103501-
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Journal article (peer-reviewed)abstract
- The performance of quantum dots-in-a-well infrared photodetectors (DWELL IPs) has been studied by means of interband and intersubband photocurrent measurements as well as dark current measurements. Using interband photocurrent measurements, substantial escape of electrons from lower lying states in the DWELL structure at large biases was revealed. Furthermore, a significant variation in the escape probability from energy states in the DWELL structure with applied bias was observed. These facts can explain the strong temperature and bias dependence of both photocurrent and dark currents in DWELL IPs.
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| 3. |
- Höglund, Linda, 1974-, et al.
(author)
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Bias mediated tuning of the detection wavelength in asymmetrical quantum dots-in-a-well infrared photodetectors
- 2008
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In: Applied Physics Letters. - New York : AIP Publishing. - 0003-6951 .- 1077-3118. ; 93:20
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Journal article (peer-reviewed)abstract
- Bias-mediated tuning of the detection wavelength within the infrared wavelength region is demonstrated for quantum dots-in-a-well and dots-on-a-well infrared photodetectors. By positioning the InAs quantum dot layer asymmetrically in an 8 nm wide In0.15Ga0.85As/GaAs quantum well, a shift in the peak detection wavelength from 8.4 to 10.3 mu m was observed when reversing the polarity of the applied bias. For a dots-on-a-well structure, the peak detection wavelength was tuned from 5.4 to 8 mu m with small changes in the applied bias. These tuning properties could be essential for applications such as modulators and dual-color infrared detection.
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| 4. |
- Höglund, Linda, 1974-, et al.
(author)
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Origin of photocurrent in lateral quantum dots-in-a-well infrared photodetectors
- 2006
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In: Applied Physics Letters. - New York : American Institute of Physics. - 0003-6951 .- 1077-3118. ; 88:21
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Journal article (peer-reviewed)abstract
- Interband and intersubband transitions of lateral InAs/In0.15Ga0.85As dots-in-a-well quantum dot infrared photodetectors were studied in order to determine the origin of the photocurrent. The main intersubband transition contributing to the photocurrent (PC) was associated with the quantum dot ground state to the quantum well excited state transition. By a comparison between intersubband PC measurements and the energy level scheme of the structure, as deduced from Fourier transform photoluminescence (FTPL) and FTPL excitation spectroscopies, the main transition contributing to the PC was identified.
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| 5. |
- Höglund, Linda, 1974-, et al.
(author)
-
Optical pumping as artificial doping in quantum dots-in-a-well infrared photodetectors
- 2009
-
In: Applied Physics Letters. - New York : AIP Publishing. - 0003-6951 .- 1077-3118. ; 94:5, s. 053503-
-
Journal article (peer-reviewed)abstract
- Resonant optical pumping across the band gap was used as artificial doping in InAs/In0.15Ga0.85As/GaAs quantum dots-in-a-well infrared photodetectors. By selectively increasing the electron population in the different quantum dot energy levels, the low temperature photocurrent peaks observed at 120 and 148 meV, could be identified as intersubband transitions emanating from the quantum dot ground state and the quantum dot excited state, respectively. With efficient filling of the quantum dot energy levels through simultaneous optical pumping into the ground states and the excited states of the quantum dots, the response was increased by a factor of 10.
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| 6. |
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| 7. |
- Höglund, Linda, 1974-, et al.
(author)
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Energy level scheme of InAs/InxGa1-xAs/GaAs quantum-dots-in-a-well infrared photodetector structures
- 2010
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In: Physical Review B. Condensed Matter and Materials Physics. - Woodbury, NY : American Physical Society. - 1098-0121 .- 1550-235X. ; 82:3, s. 035314-
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Journal article (peer-reviewed)abstract
- A thorough investigation of quantum-dots-in-a-well structures for infrared photodetector applications has been performed employing different experimental techniques. The electronic structure of self-assembled InAs quantum dots embedded in an In0.15Ga0.85As/GaAs quantum well (QW) was deduced from photoluminescence (PL) and PL excitation (PLE) spectroscopy. From polarization-dependent PL it was revealed that the quantum dots hold two electron energy levels and two heavy-hole levels. Tunnel capacitance spectroscopy confirmed an electron energy level separation of about 50 meV, and additionally, that the conduction-band ground state and excited state of the dots are twofold and fourfold degenerates, respectively. Intersubband photocurrent spectroscopy, combined with simultaneous interband pumping of the dots, revealed a dominant transition at 150 meV (8.5 mu m) between the ground state of the quantum dots and the excited state of the QW. Results from detailed full three-dimensional calculations of the electronic structure, including effects of composition intermixing and interdot interactions, confirm the experimentally unravelled energy level scheme of the dots and well.
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| 8. |
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| 9. |
- Raj, Pushparani, et al.
(author)
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Fabrication and characterisation of a silicon-borosilicate glass microfluidic device for synchrotron-based hard X-ray spectroscopy studies
- 2021
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In: RSC Advances. - Cambridge : RSC Publishing. - 2046-2069. ; 11:47, s. 29859-29869
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Journal article (peer-reviewed)abstract
- Some of the most fundamental chemical building blocks of life on Earth are the metal elements. X-ray absorption spectroscopy (XAS) is an element-specific technique that can analyse the local atomic and electronic structure of, for example, the active sites in catalysts and energy materials and allow the metal sites in biological samples to be identified and understood. A microfluidic device capable of withstanding the intense hard X-ray beams of a 4th generation synchrotron and harsh chemical sample conditions is presented in this work. The device is evaluated at the K-edges of iron and bromine and the L3-edge of lead, in both transmission and fluorescence mode detection and in a wide range of sample concentrations, as low as 0.001 M. The device is fabricated in silicon and glass with plasma etched microchannels defined in the silicon wafer before anodic bonding of the glass wafer into a complete device. The device is supported with a well-designed printed chip holder that made the microfluidic device portable and easy to handle. The chip holder plays a pivotal role in mounting the delicate microfluidic device on the beamline stage. Testing validated that the device was sufficiently robust to contain and flow through harsh acids and toxic samples. There was also no significant radiation damage to the device observed, despite focusing with intense X-ray beams for multiple hours. The quality of X-ray spectra collected is comparable to that from standard methods; hence we present a robust microfluidic device to analyse liquid samples using synchrotron XAS.
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