| 1. |
- Baskar, K., et al.
(författare)
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Surface morphology and localised states of GaInNAs single quantum wells grown by MOVPE
- 2003
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Ingår i: Journal of Crystal Growth. - 0022-0248 .- 1873-5002. ; 248, s. 431-436
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Tidskriftsartikel (refereegranskat)abstract
- GaInNAs/GaAs single quantum wells (QWs) have been grown by metalorganic vapour phase epitaxy (MOVPE). The surface morphology has been studied by atomic force microscopy (AFM). The density of pits observed on the surface of QW structures was found to depend on the growth temperature and dimethylhydrazine (DMHy) flow. Cross-sectional AFM image showed the presence of defects at the interface of GaInNAs/GaAs. The low temperature photoluminescence characteristics of the QWs as a function of growth temperature. DMHy flow and density of surface pits have been discussed. The origin of pit formation is addressed based on the pyrolysis products present during the growth of QWs. The results suggest that higher growth temperature maybe desirable to obtain good quality GaInNAs QWS.
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| 2. |
- Douheret, O., et al.
(författare)
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Characterization of GaAs/AlGaAs laser mesas regrown with semi-insulating GaInP by scanning capacitance microscopy
- 2002
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 81:6, s. 960-962
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Tidskriftsartikel (refereegranskat)abstract
- In this work, cross-sectional scanning capacitance microscopy (SCM) is used to investigate GaAs/AlGaAs buried heterostructure lasers. Laser mesas are buried with GaInP:Fe selectively regrown by hydride vapor phase epitaxy. It is shown that a complete 2D map of the electrical properties of device structure including, delineation of regrown interfaces and electrical nature of the regrown GaInP layer can be obtained. The behavior of the SCM signal with ac bias is used to verify the semi-insulating nature of the regrown layer at different locations of the sample. The measured SCM signal for the regrown GaInP:Fe layer is uniformly zero, indicating very low free carrier densities and confirming semi-insulating properties. This observation strongly suggests, in addition, uniform Fe incorporation in the regrown layers, close to and far away from the mesa. Finally, a nanoscale feature in the SCM contrast appearing as a bright (dark) spot in dC/dV mode (feedback bias mode) is observed at the mesa sidewall close to the interface between the regrown GaInP:Fe and the p-cladding layer. The origin of this contrast is discussed in terms of local band-bending effects and supported by 2D Poisson simulations of the device structure.
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| 3. |
- Douheret, O., et al.
(författare)
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Determination of spatial resolution in atomic-force-microscopy-based electrical characterization techniques using quantum well structures
- 2005
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Ingår i: Journal of Vacuum Science & Technology B. - : American Vacuum Society. - 1071-1023 .- 1520-8567. ; 23:1, s. 61-65
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Tidskriftsartikel (refereegranskat)abstract
- In this work, a procedure to determine the spatial resolution in scan ning capacitance (SCM) and scanning spreading resistance microscopy (SSRM) is proposed and demonstrated. It is based on profiling of confined carriers (in cross section) in quantum well (QW) structures consisting of QWs with different well widths and interwell spacing. Spatial resolution of sub-5 nm was observed for SSRM with commercially available diamond-coated silicon probes and sub-30 nm for SCM with IrPt5-coated probes. The influence of experimental parameters such as tip-sample bias and tip averaging on lateral resolution is discussed and appropriate measurement conditions for performing high-resolution measurements are highlighted. Finally, it is proposed that such structures can be used not only to select probes appropriate for high resolution measurements, but also in the development of new probes.
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| 4. |
- Maknys, K., et al.
(författare)
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Electrical characterization of InGaAs/InP quantum wells by scanning capacitance microscopy
- 2003
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 83:20, s. 4205-4207
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Tidskriftsartikel (refereegranskat)abstract
- In this work, cross-sectional scanning capacitance microscopy (SCM) is used to investigate InGaAs/InP quantum wells. It is demonstrated that SCM is indeed capable of detecting the electrons in the quantum wells and that the SCM signal shows a systematic trend for the different wells. Clear dips in the dC/dV signal are observed at the InGaAs quantum wells and imply carrier densities higher than the surrounding barriers. It is also shown that the depletion regions in the barriers adjacent to the wells can be resolved. The results show that geometric tip-averaging effects significantly influence the imaging of electrons in quantum wells and limit the lateral resolution.
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| 5. |
- Maknys, K., et al.
(författare)
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Probing carriers in two-dimensional systems with high spatial resolution by scanning spreading resistance microscopy
- 2003
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 83:11, s. 2184-2186
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Tidskriftsartikel (refereegranskat)abstract
- In this work, cross-sectional scanning spreading resistance microscopy (SSRM) is used to profile carriers in quantum wells (QWs). The investigated structures consist of InGaAs wells of different widths sandwiched between Si-doped InP barriers. It is demonstrated that SSRM is indeed capable of detecting electrons in the quantum wells with high lateral resolution and that the SSRM signal shows a systematic trend for the different wells. Clear dips in the resistance signal are observed at the quantum wells and imply accumulated electron densities higher than in the surrounding barriers. Carrier density in the QW is found by using the calibration curve obtained from the resistance measurements on reference layers sample. It is also shown that only at certain appropriate tip-sample bias conditions the depletion regions in the barriers adjacent to the wells are resolved. Finally, we demonstrate that under very low forward biases the full width at half maximum of the observed resistance dips in SSRM data is nearly equal to the geometric QW widths.
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| 6. |
- Mitraka, Evangelia, et al.
(författare)
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Solution processed liquid metal-conducting polymer hybrid thin films as electrochemical pH-threshold indicators
- 2015
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Ingår i: Journal of Materials Chemistry C. - : Royal Society of Chemistry. - 2050-7526 .- 2050-7534. ; 3:29, s. 7604-7611
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Tidskriftsartikel (refereegranskat)abstract
- A global and accurate mapping of the environment could be achieved if sensors and indicators are mass-produced at low cost. Printed electronics using polymeric (semi) conductors offer a platform for such sensor/indicator based circuits. Herein, we present the material concept for an electrochemical pH-threshold indicator based on a printable hybrid electrode which comprises a liquid metal alloy (GaInSn) embedded in a conducting polymer matrix (PEDOT). This hybrid electrode displays a large variation in open circuit potential versus pH in an electrochemical cell, which when connected to the gate of an electrochemical transistor leads to a dramatic change in the drain current in a narrow range of pH.
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