| 41. |
- Jain, Vishal, 1989-, et al.
(författare)
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A comparative study of nanowire based infrared p+-i-n+ photodetectors
- 2012
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Konferensbidrag (refereegranskat)abstract
- We present a comparative study of electrical and optical properties of two types of p+-i-n+ photodetectors based on self-assembled ensembles of vertical InP nanowires (NWs) monolithically grown on InP. The detectors differ in the type of p+ contact, one detector geometry has p+-i-n+ segments integrated into the NWs (type A) while the other detector has i-n+ NW segments grown directly on a p+ substrate(type B). The samples were prepared by first depositing 80 nm Au nanoparticles on a p+ InP substrate using an aerosol technique and subsequently growing NWs using MOVPE. The NWs have a polytypecrystal structure of alternating wurtzite and zincblende segments. The processing of the detectors include deposition of SiO2, followed by an etching step to remove the oxide from the tip of the NWs, and finally sputtering of ITO on 1x1 mm2 device areas. The two most prominent differences between the detectors concern the current-voltage (I-V) characteristics and the spatial location of generated photocurrent. From spectrally resolved photocurrent measurements, we conclude that the photocurrent in detector type A is primarily generated in the NWs, whereas the photocurrent in type B detectors mainly stems from the substrate. Photogenerated carriers in the substrate diffuse to the NWs where they are effectively funnelled into the NWs. The I-V characteristics of the type A detector displays a non-trivial transport behaviour for forward biases, whereas type B shows excellent rectifying behavior with an ideality factor of about 2.5. We will discuss detailed analysis of the spectral fingerprints of the two detector types revealing the mixed crystal phase of the polytype NWs and bandstructure effects, temperature dependence of the I-V characteristics and typical photodetector parameters.
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| 42. |
- Johansson, Mikael, et al.
(författare)
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Correlation between overgrowth morphology and optical properties of single self-assembled InP quantum dots
- 2003
-
Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 68:12
-
Tidskriftsartikel (refereegranskat)abstract
- We have studied the early stages of GaInP overgrowth on InP quantum dots (QD's) experimentally and theoretically. A direct correlation between the surface morphology and the optical properties of individual InP QD's is made using scanning tunneling microscopy (STM) and scanning tunneling luminescence. The geometric structure of the islands is further investigated using cross-sectional transmission electron microscopy (TEM). The overgrowth occurs in three stages; initially the InP QD's act as seeding points for the overgrowth, where the GaInP grows laterally from the side facets of the QD. The growth occurs preferentially in the [110] direction and elongated GaInP/InP islands are formed. As the overgrowth continues the islands increase laterally in size and GaInP also starts to grow between the islands, but not covering the top of the InP QD's. The growth of GaInP on top of the QD's commences once the islands have begun to coalesce. Using a model based on the STM and TEM results the electronic structures of the QD's have been calculated by eight-band k.p theory. The calculations are in good agreement with the experimental results. Our findings unravel the details of the strain induced energy shift of the QD luminescence previously reported [Pistol , Appl. Phys. Lett. 67, 1438 (1995)].
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| 43. |
- Junno, Tobias, et al.
(författare)
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Single-electron devices via controlled assembly of designed nanoparticles
- 1999
-
Ingår i: Microelectronic Engineering. - 0167-9317. ; 47:1-4, s. 179-183
-
Tidskriftsartikel (refereegranskat)abstract
- Single-electron transistors (SET) rely for their functionality on extreme control of lithography and lateral positioning as well as of properties of the building blocks from which the devices are built. By an aerosol-based nanoparticle fabrication we can prepare nanocrystals down to sub-10nm dimensions with metallic or semiconducting character, as well as having a core + shell design for definition of tunnel-gaps. We present here results for a type of device that is based on the possibility to design functionality in the internal structure of the nanoparticles which are used as building blocks. We use such pre-fabricated building blocks to construct coulomb blockade devices and show that they operate at temperatures above 150K.
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| 44. |
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| 45. |
- Karlsson, Reine, et al.
(författare)
-
Flervetenskaplig ljusforskning
- 2011
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Rapport (populärvet., debatt m.m.)abstract
- Den här skriften handlar om ljus och ljusets betydelse för oss människor. Tolv forskare med vitt skilda bakgrunder samlas och diskuterar frågor som skrider över gränserna. Vad är ljus egentligen? Hur kan vi förstå ljus? Hur påverkar det oss? På vilket sätt kan vi använda oss av det? Vilka tekniska möjligheter har vi att skapa och styra olika sorters ljus? Vilka möjligheter ger det oss inför framtiden? I centrum för dialogen står samarbete och nytänkande. Här ges en inblick i perspektiv på ljus från områden som biologi, teknik, material, fysik, estetik, filosofi, medicin och psykologi, vilka sammantaget, på ett åskådligt och lättbegripligt sätt, presenterar den flervetenskapliga ljusrelaterade kompetensen i Lund. Gruppen av experter hoppas att de frågor som ställs och de svar som ges i den här skriften ska inspirera och leda vidare inom fältet ljusforskning. Tillsammans med Pufendorfinstitutet, genom vilket expertgruppens initiativ getts möjlighet att växa och utvecklas, vill de med andra ord att sätta ljuset på...just ”ljuset”!
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| 46. |
- Karlström, Olov, et al.
(författare)
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Analysing the capacitance–voltage measurements of vertical wrapped-gated nanowires
- 2008
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 19:43
-
Tidskriftsartikel (refereegranskat)abstract
- The capacitance of arrays of vertical wrapped-gate InAs nanowires is analysed. With the help of a Poisson–Schrödinger solver, information about the doping density can be obtained directly. Further features in the measured capacitance–voltage characteristics can be attributed to the presence of surface states as well as the coexistence of electrons and holes in the wire. For both scenarios, quantitative estimates are provided. It is furthermore shown that the difference between the actual capacitance and the geometrical limit is quite large, and depends strongly on the nanowire material.
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| 47. |
- Lee, S. -K, et al.
(författare)
-
Reduction of the barrier height and enhancement of tunneling current of titanium contacts using embedded Au nano-particles on 4H and 6H silicon carbide
- 2002
-
Ingår i: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 389-393:2, s. 937-940
-
Tidskriftsartikel (refereegranskat)abstract
- We have investigated the electrical characteristics of Ti Schottky contacts with embedded Au nano-particles on various types of epilayers of SiC (4H- and 6H-SiC). From our current-voltage (I-V) and capacitance-voltage (C-V) measurements, we observed that Ti Schottky contacts with embedded Au nano-particles had 0.19 eV (n-4H-SiC) and 0.15 eV (n-6H-SiC) lower barrier height than those of particle free Ti Schottky contacts. In order to understand this reduction of the Schottky barrier height (SBH) for Ti Schottky contacts with embedded Au nano-particles, it has been proposed that SBH lowering is caused by an enhanced electric field due to the small size of the Au nano-particles and the large SBH difference. We have also tested these contacts on highly doped n-and p-type SiC material to study ohmic contacts using linear TLM measurements.
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| 48. |
- Lee, S. K., et al.
(författare)
-
Reduction of the Schottky barrier height on silicon carbide using Au nano-particles
- 2002
-
Ingår i: Solid-State Electronics. - 0038-1101 .- 1879-2405. ; 46:9, s. 1433-1440
-
Tidskriftsartikel (refereegranskat)abstract
- By the incorporation of size-selected Au nano-particles in Ti Schottky contacts on silicon carbide, we could observe considerably lower the barrier height of the contacts. This result could be obtained for both n- and p-type Schottky contacts using current-voltage and capacitance voltage measurements. For n-type Schottky contacts, we observed reductions of 0.19-0.25 eV on 4H-SiC and 0.15-0.17 eV on 6H-SiC as compared with particle-free Ti Schottky contacts. For p-type SiC, the reduction was a little lower with 0.02-0.05 eV on 4H- and 0.10-0.13 eV on 6H-SiC. The reduction of the Schottky barrier height is explained using a model with enhanced electric field at the interface due to the small size of the circular patch and the large difference of the barrier height between Ti and Au.
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| 49. |
- Lewen, R., et al.
(författare)
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High frequency characterization of a GaInAs/InP electronic waveguide T-branch switch
- 2002
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 91:4, s. 2398-2402
-
Tidskriftsartikel (refereegranskat)abstract
- We report comprehensive microwave measurements on a T-branch switch; a GaInAs/InP electron waveguide based structure. The study includes a small signal model of the device where limitations of high frequency operation are discussed. An example of large signal operation where the nonlinearity of the device is exploited by operating the T-branch switch as a frequency multiplier is demonstrated.
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| 50. |
- Lind, Erik, et al.
(författare)
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Improved subthreshold slope in an InAs nanowire heterostructure field-effect transistor
- 2006
-
Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 6:9, s. 1842-1846
-
Tidskriftsartikel (refereegranskat)abstract
- An n-type InAs/InAsP heterostructure nanowire field-effect transistor has been fabricated and compared with a homogeneous InAs field-effect transistor. For the same device geometry, by introduction of the heterostructure, the threshold voltage is shifted 4 V, the maximum current on-off ratio is enhanced by a factor of 10 000, and the subthreshold swing is lowered by a factor 4 compared to the homogeneous transistor. At the same time, the drive current remains constant for a fixed gate overdrive. A single nanowire heterostructure transistor has a transconductance of 5 mu A/V at a low source-drain voltage of 0.3 V. For the homogeneous InAs transistor, we deduced a high electron mobility of 1500 cm(2)/Vs.
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