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Three-terminal Ge dot/SiGe quantum-well photodetectors for near-infrared light detection
Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics . Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics . Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics . Linköping University, The Institute of Technology.
2006 (English)In: Applied Physics Letters, ISSN 0003-6951, Vol. 89, 083510-083513 p.Article in journal (Refereed) Published
Abstract [en]

A three-terminal metal-oxide-semiconductor field-effect transistor type of photodetector has been fabricated with a multiple stack of Ge dot/SiGe quantum-well heterostructures as the active region for light detection at 1.3–1.55  µm. Gate-dependent edge incidence photoconductivity measurements at room temperature revealed a strong dependence of the photoresponse on the gate voltage. At positive gate bias, the hole transport from the dots into the wells was improved, resulting in a faster response. The high photoresponsivity at negative VG, measured to be 350  mA  W–1 at 1.31  µm and 30  mA  W–1 at 1.55  µm, was ascribed to the photoconductive gain.

Place, publisher, year, edition, pages
2006. Vol. 89, 083510-083513 p.
Keyword [en]
germanium, Ge-Si alloys, elemental semiconductors, semiconductor quantum wells, photodetectors, MOSFET, photoconductivity
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:liu:diva-12573DOI: 10.1063/1.2337867OAI: oai:DiVA.org:liu-12573DiVA: diva2:1726
Available from: 2008-09-15 Created: 2008-09-15 Last updated: 2009-05-11
In thesis
1. Si-based structures for light emission and detection
Open this publication in new window or tab >>Si-based structures for light emission and detection
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Efforts to improve the optical performance of the indirect bandgap semiconductor silicon (Si) has been a major subject of research in the field of Si photonics due to the promising applications of Si based light emitters and detectors for optical communication. With that motivation three different Si based material systems were investigated; Si:Er/O layered structures, SiGe quantum dots and SiSn nano structures, all grown using the technique of molecular beam epitaxy (MBE). The main focus of this work has been on Si:Er/O layers, which lead to fabrication of Si-based light emitting diodes (LED) emitting at 1.54 mm wavelength. The work on SiGe structures lead to the fabrication of near-infrared light detectors, whereas the SiSn structures have not shown any strong optical character.

Studies include epitaxial growth, structural characterization, device processing, electrical and optical characterizations. Material characterization of Si:Er/O structures using analytical electron microscopy (AEM) revealed interesting results with identification of two different type of microstructures in these layers depending on the Er and O concentrations. Several Si:Er/O LEDs were fabricated with different Er and O concentrations and the optical characteristics were investigated in order to find the best doping levels of Er and O for efficient light emission. The electroluminescence measurements revealed a strong 1.54 mm emission from these devices due to the intra 4f shell transition of Er3+ from the excited state (4I13/2) to the ground state (4I15/2). Si:Er/O waveguide LEDs have also been grown on SOI wafers using the optimized structure parameters obtained from mode confinement simulations as well as the microstructure investigations. The Si:Er/O waveguide LEDs are aimed at fabricating a planar Si cavity with Bragg mirrors on both sides to obtain light amplification and realise an electrically pumped Si laser. A focused ion beam (FIB) instrument was used to fabricate the Bragg mirrors but initial attempts did not result in light amplification in our Si:Er/O waveguide cavities.

SiGe quantum dots are well-known quantum structures which are formed in a selfassembled fashion from Si/SiGe layer structures with a variety of shapes, sizes and compositions depending mainly on parameters like growth temperature and layer thicknesses. Optical properties of SiGe quantum structures have been studied while there has been little knowledge about their composition. A detailed compositional investigation of different SiGe dots on a nanometer scale was performed using AEM. The results showed a large degree of interdiffusion in large quantum dots, which was consistent with the optical properties of these dots. Using a multiple stack of Ge quantum dots and SiGe quantum wells, MOSFET type photodetectors working at 1.3 – 1.55 mm wavelength have also been fabricated and characterized.

Research on the SiSn system was mainly motivated by the possibility to obtain a direct bandgap transition in Si based material as it was predicted theoretically and experimentally observed in the related GeSn material system by other researchers. Structural and optical characterizations of SiSn nano structures were performed. Although the same SiSn nano structures exhibit a weak signature of optical absorption, low temperature photoluminescence measurements did not reveal any emission peaks related to the SiSn dots.

Abstract [sv]

Kisel är den helt dominerande halvledaren för tillverkning av de integrerade kretsar som utgör grunden för vårt nuvarande IT-samhälle. Samtidigt har det inte varit möjligt att använda kisel-komponenter inom det stora optoelektronikområdet, exempelvis i sändare och mottagare för fiberoptisk kommunikation. På grund av de stora fördelar det skulle innebära att kunna integrera optoelektronik med kiselbaserade komponenter på samma halvledarskiva så har det under de senaste åren varit mycket forskning kring möjligheterna att modifiera kisel så att det kan användas inom optoelektronik.

I denna avhandling har tre olika materialkombinationer studerats för att undersöka om kiselbaserade material kan användas för emission eller detektion av optiska signaler. Den största delen av arbetet handlar om att tillverka, studera och utnyttja strukturer med låga halter av erbium och syre som kan fungera som lysdioder i det infraröda området med just den våglängd, 1,54 μm, som används i de flesta fall av fiberoptisk kommunikation. Genom att studera hur ljusintensiteten beror på erbium- och syrekoncentrationerna samt den erhållna mikrostrukturen i materialet så har tillverkningen kunnat optimerats för högsta intensitet. Vidare har multilagerstrukturer utvecklats så att ljusemissionen sker ifrån en s.k. vågledare. Målsättningen har varit att skapa möjligheter för att erhålla s.k. stimulerad emission vilket skulle resultera i en kiselbaserad laser.

En annan del av avhandlingen berör tillverkning, karakterisering och användning av s.k. germanium kvantprickar som kan erhållas på kiselytor om man belägger ytan med ett antal atomlager av germanium. Dessa öar kan sedan begravas av kisel och får intressanta optiska egenskaper. Studier har gjorts av hur stor interdiffusionen är av kisel och germanium i kvantprickarna vilket påverkar vilka ljusvåglängder som kan absorberas eller emitteras av kvantprickarna. Med hjälp av sådana kvantprickar har detektorer för våglängder 1,3-1,5 μm tillverkats och karakteriserats.

Då även tenn/kisel kvantprickar har rapporterats ge användbar absorption av vissa våglängder har en studie genomförts av tillverkning och karakterisering av material som innehåller sådana kvantprickar.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2008. 106 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1213
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-12575 (URN)978-91-7393-798-6 (ISBN)
Public defence
2008-09-25, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2008-09-15 Created: 2008-09-15 Last updated: 2009-05-04Bibliographically approved
2. Near-infrared photodetectors based on Si/SiGe nanostructures
Open this publication in new window or tab >>Near-infrared photodetectors based on Si/SiGe nanostructures
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Two types of photodetectors containing Ge/Si quantum dots have been fabricated based on materials grown by molecular beam epitaxy and characterized with several experimental techniques. The aim was to study new device architectures with the implementation of Ge nanostructures, in order to obtain high detection efficiency in the near infrared range at room temperature.

Heterojunction bipolar phototransistors were fabricated with 10 Ge dot layers in the base-collector (b-c) junction. With the illumination of near infrared radiation at 1.31 to 1.55 µm, the incident light would excite the carriers. The applied field across the b-c junction caused hole transport into the base, leading to a reduced potential barrier between the emitter-base (e-b) junction. Subsequently, this resulted in enhanced injection of electrons across the base into the collector, i.e., forming an amplified photo-induced current. We have therefore obtained significantly enhanced photo-response for the Ge-dot based phototransistors, compared to corresponding quantum dot p-i-n photodiodes. Responsivity values up to 470 mA/W were measured at 1.31 µm using waveguide geometry, and ∼2.5 A/W at 850 nm, while the dark current was as low as 0.01 mA/cm2 at –2 V.

Metal-oxide field-effect phototransistors were also studied. These lateral detectors were processed with three terminals for source, drain and gate contacts. The Ge quantum dot layers were sandwiched between pseudomorphically grown SiGe quantum wells. The detector devices were processed using a multi-finger comb structure with an isolated gate contact on top of each finger and patterned metal contacts on the side edges for source and drain. It was found that the photo-responsivity was increased by a factor of more than 20 when a proper gate bias was applied. With VG above threshold, the measured response was 350 and >30 mA/W at 1.31 and 1.55 µm, respectively.

Properties of Si/Si1-xGex nanostructures were examined, in order to facilitate proper design of the above mentioned transistor types of photodetectors. The carrier recombination processes were characterized by photoluminescence measurements, and the results revealed a gradual change from spatially indirect to direct transitions in type II Si1-xGex islands with increased measurement temperature. Energy dispersive X-ray spectrometry of buried Ge islands produced at different temperatures indicated a gradual decrease of the Ge concentration with temperature, which was due to the enhanced intermixing of Si and Ge atoms. At a deposition temperature of 730°C the Ge concentration was as low as around 40 %.

Finally, the thermal stability of the Si/SiGe(110) material system, which is a promising candidate for future CMOS technology due to its high carrier mobility, was investigated by high resolution X-ray diffraction reciprocal space mapping. Anisotropic strain relaxation was observed with maximum in-plane lattice mismatch in the [001] direction.

Place, publisher, year, edition, pages
Institutionen för fysik, kemi och biologi, 2006
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1003
Keyword
SiGe, Ge dots, nanostructures, molecular beam epitaxy, photodetector
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-5909 (URN)91-85497-24-X (ISBN)
Public defence
2006-02-27, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Note
On the day of the defence date the status of article IV was Manuscript and the title was "A three-terminal Ge dot/SiGe quantum well MOSFET photodetector for near infrared light detection"; the status of article VI was Submitted and the title was "Band alignment studies in Si/Ge quantum dots based on optical and structural investigations"; the status of article VII was Manuscript and the title was "Thermal stability of SiGe/Si(110) investigated by high-resolution X-ray diffraction reciprocal space mapping".Available from: 2006-02-27 Created: 2006-02-27 Last updated: 2009-02-18

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Elfving, AndersKarim, AmirHansson, Göran V.Ni, Wei-Xin

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