Towards ultraviolet and blue microcavity lasers

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Bergmann, Michael Alexander,1989Chalmers tekniska högskola,Chalmers University of Technology (author)

Towards ultraviolet and blue microcavity lasers

Article/chapterEnglish2018

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2018

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LIBRIS-ID:oai:research.chalmers.se:2ffc19e7-3ba8-4490-ba53-e5e80da8381c
https://research.chalmers.se/publication/532824URI

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Language:English
Summary in:English

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Subject category:kon swepub-publicationtype
Subject category:ref swepub-contenttype

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The development of III-nitride-based (Al,Ga,In(N)) microcavity lasers is a challenging task. Significant progress in recent years has resulted in realizations of electrically pumped devices with optical output power in the mW-range and with threshold current densities below 20 kA/cm2. However, to become practical, the lifetime and power conversion efficiency of these devices must be improved. Among the challenges are achieving transverse optical mode confinement, highreflectivity mirrors and control over the resonator length. We will highlight our theoretical work on transverse optical mode confinement, emphasising the overwhelming risk of ending up with an optically anti-guided cavity, and its consequences such as very high optical losses that easily could double the threshold gain for lasing. We will show some anti-guided cavities with reasonable threshold gain and built-in modal discrimination. However, all anti-guided cavities are very sensitive to temperature effects and small structural changes in the cavity caused by fabrication imperfections. We have explored electrically conductive distributed Bragg reflectors (DBRs) in both AlN/GaN and ZnO/GaN. The AlN/GaN DBRs were grown with different strain-compensating interlayers, and the DBR without interlayers had the lowest vertical resistivity with a specific series resistance of 0.044 cmfor eight DBRpairs. In the ZnO/GaN DBR, the measured resistance was dominated by lateral and contact contributions, setting a lower measurable limit of ~10 for three DBR-pairs. Numerical simulations show the importance of having in-plane strained layers in the ZnO/GaN DBR, since that leads to cancellation of the spontaneous and piezoelectric polarization. This results in a dramatically reduced vertical resistance, potentially three orders of magnitude lower than what could be measured. cm An alternative to an epitaxially grown DBR is a dielectric DBR, which offers high reflectivity over a broader wavelength range, relaxing the requirements on resonator length control. To deposit a dielectric DBR on the bottom side of the cavity, the sample must first be bonded to a carrier wafer before the substrate can be removed. We used thermocompression gold-gold bonding to successfully bond the laser structure to a Si carrier wafer. The subsequent substrate removal is a challenging process due to the chemical inertness of the III-nitride-based materials. A doping-dependent electrochemical etch technique was used, which allows for the selective removal of a sacrificial (n-doped) layer between the cavity and the substrate. This resulted in nm-precise cavity lift-off with a low root-mean-square surface roughness down to 0.3 nm. Thus, the process is suitable for the fabrication of high-quality optical devices such as microcavity lasers. In addition, the technique offers a new alternative to create III-nitridebased optical resonators, mechanical resonators, thin film LEDs and transistors.

Subject headings and genre

NATURVETENSKAP Fysik hsv//swe
NATURAL SCIENCES Physical Sciences hsv//eng
TEKNIK OCH TEKNOLOGIER Materialteknik Annan materialteknik hsv//swe
ENGINEERING AND TECHNOLOGY Materials Engineering Other Materials Engineering hsv//eng
TEKNIK OCH TEKNOLOGIER Elektroteknik och elektronik hsv//swe
ENGINEERING AND TECHNOLOGY Electrical Engineering, Electronic Engineering, Information Engineering hsv//eng
TEKNIK OCH TEKNOLOGIER Nanoteknik hsv//swe
ENGINEERING AND TECHNOLOGY Nano-technology hsv//eng
ultraviolet
electrochemical etching
microcavity laser
DBR
blue

Added entries (persons, corporate bodies, meetings, titles ...)

Hjort, Filip,1991Chalmers tekniska högskola,Chalmers University of Technology(Swepub:cth)filiphj (author)
Hashemi, Seyed Ehsan,1986Chalmers tekniska högskola,Chalmers University of Technology(Swepub:cth)eseyed (author)
Adolph, David,1971Chalmers tekniska högskola,Chalmers University of Technology(Swepub:cth)adolph (author)
Stattin, Martin,1983Chalmers tekniska högskola,Chalmers University of Technology(Swepub:cth)stattin (author)
Ive, Tommy,1968Chalmers tekniska högskola,Chalmers University of Technology(Swepub:cth)itommy (author)
Bengtsson, Jörgen,1968Chalmers tekniska högskola,Chalmers University of Technology(Swepub:cth)jorgenb (author)
Gustavsson, Johan,1974Chalmers tekniska högskola,Chalmers University of Technology(Swepub:cth)johangus (author)
Haglund, Åsa,1976Chalmers tekniska högskola,Chalmers University of Technology(Swepub:cth)gu95asha (author)
Chalmers tekniska högskola (creator_code:org_t)

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In:Northen Optics and Photonics conference20189789163964886

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