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Origin of photoresponse at 8-14 μm in stacks of self-assembled SiGe/Si quantum dots
Linköpings universitet, Institutionen för fysik, kemi och biologi, Yt- och Halvledarfysik. Linköpings universitet, Tekniska högskolan.
Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.ORCID-id: 0000-0002-4547-6673
Linköpings universitet, Institutionen för fysik, kemi och biologi, Yt- och Halvledarfysik. Linköpings universitet, Tekniska högskolan.
Linköpings universitet, Institutionen för fysik, kemi och biologi, Yt- och Halvledarfysik. Linköpings universitet, Tekniska högskolan.
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2009 (Engelska)Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235XArtikel i tidskrift (Övrigt vetenskapligt) Submitted
Abstract [en]

A normal incidence photodetector operating at 8-14 μm is demonstrated using p-type δ-doped SiGe dot multilayer structures grown by molecular beam epitaxy on Si(001) substrates. Based on the experimental results of photoluminescence and photoluminescence excitation spectroscopies together with numerical analysis, the origin of the measured photocurrent was attributed to intersubband optical transitions between the heavy hole and light hole states of the valence band of the self-assembled SiGe dots and subsequent lateral transport of photo-excited carriers in the conduction channels formed by Ge wetting layers.

Ort, förlag, år, upplaga, sidor
2009.
Nationell ämneskategori
Naturvetenskap
Identifikatorer
URN: urn:nbn:se:liu:diva-53203OAI: oai:DiVA.org:liu-53203DiVA, id: diva2:287740
Tillgänglig från: 2010-01-19 Skapad: 2010-01-19 Senast uppdaterad: 2017-12-12
Ingår i avhandling
1. Optical characterization of Silicon-based self-assembled nanostructures
Öppna denna publikation i ny flik eller fönster >>Optical characterization of Silicon-based self-assembled nanostructures
2010 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

This PhD thesis summarizes the work carried on the optical characterizations of some Si-based self-assembled nanostructures, particularly SiGe/Si quantum dots (QDs) and nanocrystalline (nc)-Si embedded in mesoporous silica (MS) using photoconductivity (PC), photoluminescence (PL), and photoluminescence excitation (PLE) measurements.

The spectroscopic studies of SiGe/Si QDs grown on Si by molecular beam epitaxy revealed for the first time well-resolved PLE resonances. When correlated with numerical analysis, these resonances were directly related to the co-existence of spatially direct (inside the SiGe dot) and indirect (across the Si/Ge interface) recombination processes involving different dot populations selected by the monitored detection energy for PLE acquisition. The characteristics of these two transitions were further studied in detail by PLE (in some case implemented together with selective PL) on various samples, which contained either only one Ge dot layer or multiple Gedot/Si stacks, grown at substrate temperatures ranging from 430 to 580 °C; especially the temperature- and excitation power-dependence of the excitation properties. The results illustrated that the electronic structure of SiGe dots are influenced by size, Ge composition, as well as strain connected, and sometimes a mixed effect.

Another attempt of the project was the fabrication of lateral transport mid-infrared photodetectors based on multiple Ge-dot/Si stacked structures. A broadband photoresponsivity of the processed multi-finger detectors was estimated to be about 90 mA/W over 3-15 μm range at 20 K, and the peaked photoresponse was measured at ~10 μm. The origin of the measured photocurrent, as elucidated by photoluminescence and photoluminescence excitation spectroscopies, was related to intersubband absorption of normal incidence infrared radiation corresponding to energies between the ground states of the heavy hole and the light hole in the valence band of the SiGe/Si QDs, and subsequent charge transfer to the Ge 2D wetting layer acting as a conduction channel. The absence of photocurrent in the energy range expected for a transition from the ground state to the first excited state of the heavy hole indicated that the holes in the SiGe dots behave essentially as 2D in character rather than a truly 3D confinement, where the transitions between heavy holes states are not allowed for TE polarized radiation (normal incidence).

Finally, Si(or Ge) nanocrystals embedded in mesoporous silica samples prepared by spincoating and atomic layer chemical vapor deposition were optically investigated by means of PL with various excitation powers, together with several attempts using different post rapid thermal annealing processes. The shape and energy position of the PL spectra of the nc-Si embedded in MS samples and a reference MS template without nc incorporation were rather similar, but the luminescence was much more intense for those embedded with nanocrystals. This implies that the emission mechanism for MS samples with or without nc-Si could be the same, i.e., the light emission was governed by the surface properties of silica. The semiconductor nanocrystals played a role by sensitizing the luminescence emission through generating more photo-excited carriers. These carriers were then trapped in the defect state e.g. the interfacial oxygen defect sites and subsequently recombine to increase the PL intensity.

Ort, förlag, år, upplaga, sidor
Linköping: Linköping University Electronic Press, 2010. s. 54
Serie
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1296
Nationell ämneskategori
Naturvetenskap
Identifikatorer
urn:nbn:se:liu:diva-53206 (URN)978-91-7393-358-2 (ISBN)
Disputation
2010-06-17, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (Engelska)
Opponent
Handledare
Tillgänglig från: 2010-01-19 Skapad: 2010-01-19 Senast uppdaterad: 2011-02-04Bibliografiskt granskad

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Adnane, BouchaibKarlsson, FredrikZhao, MingHansson, GöranHoltz, Per-OlofNi, Wei-Xin

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