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Optimising uniformity of InAs/(InGaAs)/GaAs quantum dots grown by metal organic vapor phase epitaxy
Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
Acreo AB, Electrum 236, S-164 40 Kista, Sweden.
Acreo AB, Electrum 236, S-164 40 Kista, Sweden.
Acreo AB, Electrum 236, S-164 40 Kista, Sweden.
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2006 (English)In: Applied Surface Science, ISSN 0169-4332, Vol. 252, no 15, 5525-5529 p.Article in journal (Refereed) Published
Abstract [en]

A route towards optimisation of uniformity and density of InAs/(InGaAs)/GaAs quantum dots grown by metal organic vapor phase epitaxy (MOVPE) through successive variations of the growth parameters is reported. It is demonstrated that a key parameter in obtaining a high density of quantum dots is the V/III ratio, a fact which was shown to be valid when either AsH3 (arsine) or tertiary-butyl-arsine (TBA) were used as group V precursors. Once the optimum V/III ratio was found, the size distribution was further improved by adjusting the nominal thickness of deposited InAs material, resulting in an optimum thickness of 1.8 monolayers of InAs in our case. The number of coalesced dots was minimised by adjusting the growth interruption time to approximately 30 s. Further, the uniformity was improved by increasing the growth temperature from 485 °C to 520 °C. By combining these optimised parameters, i.e. a growth temperature of 520 °C, 1.8 monolayers InAs thickness, 30 s growth stop time and TBA as group V precursor, a full-width-half-maximum (FWHM) of the low temperature luminescence band of 40 meV was achieved, indicating a narrow dot size distribution.

Place, publisher, year, edition, pages
Elsevier , 2006. Vol. 252, no 15, 5525-5529 p.
Keyword [en]
Quantum dot, Epitaxy, MOVPE, InAs/GaAs, TBA, Growth
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
URN: urn:nbn:se:liu:diva-15764DOI: 10.1016/j.apsusc.2005.12.128OAI: oai:DiVA.org:liu-15764DiVA: diva2:127226
Note
Original Publication: Linda Höglund, E. Petrini, C. Asplund, H. Malm, J. Y. Andersson and Per-Olof Holtz, Optimising uniformity of InAs/(InGaAs)/GaAs quantum dots grown by metal organic vapor phase epitaxy, 2006, Applied Surface Science, (252), 15, 5525-5529 . http://dx.doi.org/10.1016/j.apsusc.2005.12.128 Copyright: Elsevier Science B.V., Amsterdam. http://www.elsevier.com/ Available from: 2009-07-09 Created: 2008-12-03 Last updated: 2010-01-14Bibliographically approved
In thesis
1. Growth and characterisation of InGaAs-based quantum dots-in-a-well infrared photodetectors
Open this publication in new window or tab >>Growth and characterisation of InGaAs-based quantum dots-in-a-well infrared photodetectors
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents results from the development of quantum dot (QD) based infrared photodetectors (IPs). The studies include epitaxial growth of QDs, investigations of the structural, optical and electronic properties of QD-based material as well as characterisation of the resulting components.

Metal-organic vapour phase epitaxy is used for growth of self-assembled indium arsenide (InAs) QDs on gallium arsenide (GaAs) substrates. Through characterisation by atomic force microscopy, the correlation between size distribution and density of quantum dots and different growth parameters, such as temperature, InAs deposition time and V/III-ratio (ratio between group V and group III species) is achieved. The V/III-ratio is identified as the most important parameter in finding the right growth conditions for QDs. A route towards optimisation of the dot size distribution through successive variations of the growth parameters is presented.

The QD layers are inserted in In0.15Ga0.85As/GaAs quantum wells (QWs), forming so-called dots-in-a-well (DWELL) structures. These structures are used to fabricate IPs, primarily for detection in the long wavelength infrared region (LWIR, 8-14 μm).

The electron energy level schemes of the DWELL structures are revealed by a combination of different experimental techniques. From Fourier transform photoluminescence (FTPL) and FTPL excitation (FTPLE) measurements the energy level schemes of the DWELL structures are deduced. Additional information on the energy level schemes is obtained from tunneling capacitance measurements and the polarization dependence studies of the interband transitions. From tunneling capacitance measurements, the QD electron energy level separation is confirmed to be 40-50 meV and from the polarization dependence measurements, the heavy hole character of the upper hole states are revealed.

Further characterisation of the IPs, by interband and intersubband photocurrent measurements as well as dark current measurements, is performed. By comparing the deduced energy level scheme of the DWELL structure and the results of the intersubband photocurrent measurements, the origin of the photocurrent is determined. The main intersubband transition contributing to the photocurrent is identified as the QD ground state to a QW excited state transition. Optical pumping is employed to gain information on the origin of an additional photocurrent peak observed only at temperatures below 60 K. By pumping resonantly with transitions associated with certain quantum dot energy levels, this photocurrent peak is identified as an intersubband transition emanating from the quantum dot excited state. Furthermore, the detector response is increased by a factor of 10, when using simultaneous optical pumping into the quantum dots states, due to the increasing electron population created by the pumping. In this way, the potentially achievable responsivity of the detector is predicted to be 250 mA/W.

Significant variations of photocurrent and dark currents are observed, when bias and temperature are used as variable parameters. The strong bias and temperature dependence of the photocurrent is attributed to the escape route from the final state in the QW, which is limited by tunneling through the triangular barrier. Also the significant bias and temperature dependence of the dark current could be explained in terms of the strong variation of the escape probability from different energy states in the DWELL structure, as revealed by interband photocurrent measurements. These results are important for the future optimisation of the DWELL IP.

Tuning of the detection wavelength within the LWIR region is achieved by means of a varying bias across the DWELL structure. By positioning the InAs quantum dot layer asymmetrically in a 8 nm wide In0.15Ga0.85As/GaAs quantum well, a step-wise shift in the detection wavelength from 8.4 to 10.3 μm could be achieved by varying the magnitude and polarity of the applied bias. These tuning properties could be essential for applications such as odulators and dual-colour infrared detection.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2008. 70 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1226
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
urn:nbn:se:liu:diva-15774 (URN)978-91-7393-741-2 (ISBN)
Public defence
2008-12-19, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Note
On the day of the defence date the status on article IV was: Accepted.Available from: 2008-12-03 Created: 2008-12-03 Last updated: 2009-04-30Bibliographically approved
2. InGaAs-based quantum dots for infrared imaging applications: growth and characterisation
Open this publication in new window or tab >>InGaAs-based quantum dots for infrared imaging applications: growth and characterisation
2007 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, results are presented from the development of quantum dot (QD) based infrared photodetectors (IPs). This includes epitaxial growth of QDs, investigations of the structural, optical and electronic properties of the QD based material as well as characterisation of the resulting components.

Metal organic vapour phase epitaxy is used for growth of selfassembled indium arsenide (lnAs) QDs on gallium arsenide (GaAs) substrates. Through characterisation by atomic force microscopy, the correlation between size distribution and density of quantum dots and different growth parameters, such as temperature, InAs deposition time and V/III-ratio (ratio between group Vand group III species) is achieved. The V/111ratio is identified as the most important parameter, in finding the right growth conditions for QDs. A route towards optimisation of the dot size distribution through successive variations of the growth parameters is presented.

The QD layers are inserted in Ino.15Gao.85As/GaAs quantum wells (QWs), forming so-called dots-in-a-well (DWELL) structures. These structures are used to fabricate IPs, primarily for detection in the long wavelength infrared region (LWIR, 8-12 µm).

The electron energy level schemes of the DWELL structures are deduced by means of Fourier transform photoluminescence (FTPL) and FTPL excitation (FTPLE) measurements. Further characterisation of the IPs, through interband and intersubband photocurrent (pe) measurements as weIl as dark current measurements, is performed. By comparisons of the deduced energy level scheme of the DWELL structure and the results of the intersubband PC measurements, the origin of the PC is determined. The main intersubband transition contributing to the PC is identified as the QD ground state to the QW excited state transition. Significant variations of PC and dark current are observed, when voltage and temperature are used as variable parameters. A possible explanation to this could be the strong variation of the escape probability from different energy states in the DWELL structure, as revealed by interband PC measurements. These results are important for the further optimisation of the DWELL lP.

Place, publisher, year, edition, pages
Kista Snabbtryck, 2007. 49 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1297
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-52952 (URN)LIU-TEK-LIC-2007:6 (Local ID)978-91-85715-85-5 (ISBN)LIU-TEK-LIC-2007:6 (Archive number)LIU-TEK-LIC-2007:6 (OAI)
Presentation
(English)
Supervisors
Available from: 2010-01-25 Created: 2010-01-14 Last updated: 2010-01-25Bibliographically approved

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