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Optical loss and interface morphology in AlGaAs/GaAs distributed Bragg reflectors
KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.ORCID iD: 0000-0002-9040-4740
2007 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 91, no 10, 101101- p.Article in journal (Refereed) Published
Abstract [en]

It is shown that n-type doping of AlGaAs/GaAs distributed Bragg reflectors (DBRs) grown by metal-organic vapor-phase epitaxy has a profound negative impact on the performance of vertical-cavity surface-emitting lasers (VCSELs) based on such mirrors. Using an intracavity contact scheme, 1.3-mu m-range InGaAs VCSELs with and without doping in the bottom DBR are directly compared. Doped mirrors lead to lower slope efficiency, lower output power, and higher threshold current. From x-ray diffraction, high-accuracy reflectance measurements, and atomic force microscopy studies, it is suggested that this performance degradation is due to the doping-enhanced Al-Ga interdiffusion, leading to interface roughening and increased scattering loss.

Place, publisher, year, edition, pages
2007. Vol. 91, no 10, 101101- p.
Keyword [en]
Metallorganic vapor phase epitaxy; Optical losses; Semiconducting aluminum compounds; Semiconductor doping; Surface emitting lasers; X ray diffraction; High-accuracy reflectance measurements; Interface morphology; Vertical-cavity surface-emitting lasers (VCSELs)
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:kth:diva-8625DOI: 10.1063/1.2779242ISI: 000249322900001Scopus ID: 2-s2.0-34548480155OAI: oai:DiVA.org:kth-8625DiVA: diva2:13997
Note
QC 20100825Available from: 2008-06-03 Created: 2008-06-03 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Design and fabrication of long wavelength vertical cavity lasers on GaAs substrates
Open this publication in new window or tab >>Design and fabrication of long wavelength vertical cavity lasers on GaAs substrates
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Vertical cavity surface emitting lasers (VCSELs) are today a commodity on the short wavelength laser market due to the ease with which they are manufactured. Much effort has in the last decade been directed towards making long wavelength VCSELs as successful in the marketplace. This has not been achieved due to the much more difficult fabrication technologies needed for realising high performance long wavelength VCSELs. At one point, GaInNAs quantum wells gain regions grown on GaAs substrates seemed to be the solution as it enabled all-epitaxial VCSELs that could make use of high contrast AlGaAs-based distributed Bragg reflectors (DBRs) as mirrors and lateral selective oxidation for optical and electrical confinement, thereby mimicking the successful design of short wavelength VCSELs. Although very good device results were achieved, reproducible and reliable epitaxial growth of GaInNAs quantum wells proved difficult and the technology has not made its way into high-volume production. Other approaches to the manufacturing and material problems have been to combine mature InP-based gain regions with high contrast AlGaAs-based DBRs by wafer fusion or with high contrast dielectric DBRs. Commonly, a patterned tunnel junction provides the electrical confinement in these VCSELs. Excellent performance has been achieved in this way but the fabrication process is difficult.

In this work, we have employed high strain InGaAs quantum wells along with large detuning between the gain peak and the emission wavelength to realize GaAs-based long wavelength VCSELs. All-epitaxial VCSELs with AlGaAs-based DBRs and lateral oxidation confinement were fabricated and evaluated. The efficiency of these VCSELs was limited due to the optical absorption in the doped DBRs. To improve the efficiency and manufacturability, two novel optical and electrical confinement schemes based on epitaxial regrowth of current blocking layers were developed. The first scheme is based on a single regrowth step and requires very precise processing. This scheme was therefore not developed beyond the first generation but single mode power of 0.3 mW at low temperature, -10ºC, was achieved. The second scheme is based on two epitaxial regrowth steps and does not require as precise processing. Several generations of this design were manufactured and resulted in record high power of 8 mW at low temperature, 5ºC, and more than 3 mW at high temperature, 85ºC. Single mode power was more modest with 1.5 mW at low temperature and 0.8 mW at high temperature, comparable to the performance of the single mode lateral oxidation confined VCSELs. The reason for the modest single mode power was found to be a non-optimal cavity shape after the second regrowth that leads to poor lateral overlap between the gain in the quantum wells and the intensity of the optical field.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. 79 p.
Series
Trita-ICT/MAP AVH, ISSN 1653-7610 ; 2008:10
Keyword
VCSEL, Selective Area Epitaxy, Epitaxial regrowth, Laser
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-4795 (URN)978-91-7178-990-7 (ISBN)
Public defence
2008-06-12, N2, Electrum 3, Isafjordsgatan 28 A/D, Kista, 10:00
Opponent
Supervisors
Note
QC 20100825Available from: 2008-06-03 Created: 2008-06-03 Last updated: 2010-08-25Bibliographically approved
2. Epitaxial growth optimization for 1.3-um InGaAs/GaAs Vertical-Cavity Surface-Emitting lasers
Open this publication in new window or tab >>Epitaxial growth optimization for 1.3-um InGaAs/GaAs Vertical-Cavity Surface-Emitting lasers
2008 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

Long-wavelength (1.3-μm) vertical-cavity surface-emitting lasers (VCSELs) are of great interest as low-cost, high performance light sources for fiber-optic metro and access networks. During recent years the main development effort in this field has been directed towards all epitaxial GaAs-based structures by employing novel active materials. Different active region candidates for GaAs-based 1.3-μm VCSELs such as GaInNAs/GaAs QWs, GaAsSb QWs or InAs/InGaAs QDs have been investigated. However, the difficult growth and materials properties of these systems have so far hampered any real deployment of the technology. More recently, a new variety of VCSELs have been developed at KTH as based on highly strained InGaAs QWs and negative gain cavity detuning to reach the 1.3-μm wavelength window. The great benefit of this approach is that it is fully compatible with standard materials and processing methods.

The aim of this thesis is to investigate long-wavelength (1.3-μm) VCSELs using ~1.2-μm In0.4GaAs/GaAs Multiple Quantum Wells (MQWs). A series of QW structures, DBR structures and laser structures, including VCSELs and Broad Area lasers (BALs) were grown by metal-organic vapor phase epitaxy (MOVPE) and characterized by various techniques: Photoluminescence (PL), high-resolution x-ray diffraction (XRD), atomic force microscopy (AFM), high accuracy reflectance measurements as well as static and dynamic device characterization. The work can be divided into three parts. The first part is dedicated to the optimization and characterization of InGaAs/GaAs QWs growth for long wavelength and strong luminescence. A strong sensitivity to the detailed growth conditions, such as V/III ratio and substrate misorientation is noted. Dislocations in highly strained InGaAs QW structure and Sb as surfactant assisted in InGaAs QW growth are also discussed here. The second part is related to the AlGaAs/GaAs DBR structures. It is shown that the InGaAs VCSELs with doped bottom DBRs have significantly lower slope efficiency, output power and higher threshold current. By a direct study of buried AlGaAs/GaAs interfaces, this is suggested to be due to doping-enhanced Al-Ga hetero-interdiffusion. In the third part, singlemode, high-performance 1.3-μm VCSELs based on highly strained InGaAs QWs are demonstrated. Temperature stable singlemode performance, including mW-range output power and 10 Gbps data transmission, is obtained by an inverted surface relief technique.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. 51 p.
Series
Trita-ICT/MAP AVH, ISSN 1653-7610 ; 2008:4
Keyword
VCSEL MOVPE InGaAs/GaAs quantum wells
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-4648 (URN)978-91-7178-866-5 (ISBN)
Presentation
2008-03-07, Sal N2, Electrum 3, Isafjordsgatan 28, Kista, 14:00
Opponent
Supervisors
Note
QC 20101126Available from: 2008-02-25 Created: 2008-02-25 Last updated: 2010-11-26Bibliographically approved
3. Materials and Processing Technologies for Advanced Electronic and Photonic Devices
Open this publication in new window or tab >>Materials and Processing Technologies for Advanced Electronic and Photonic Devices
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Place, publisher, year, edition, pages
stockholm: KTH Royal Institute of Technology, 2014. 84 p.
Series
TRITA-ICT/MAP AVH, ISSN 1653-7610 ; 2014:15
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-157138 (URN)978-91-7595-351-9 (ISBN)
Public defence
2014-12-17, Sal/Hal A, Electrum, KTH-ICT, Kista, 10:00 (English)
Opponent
Supervisors
Note

QC 20141208

Available from: 2014-12-08 Created: 2014-12-07 Last updated: 2014-12-08Bibliographically approved

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