Processing technologies for long-wavelength vertical-cavity lasers
2001 (English)Doctoral thesis, comprehensive summary (Other scientific)
Vertical-cavity surface-emitting lasers (VCSELs) areattractive as potential inexpensive high-performance emittersfor fibre-optical communication systems. Their surface-normalemission together with the small dimensions are beneficial forlow-cost fabrication since it allows on-wafer testing,simplified packaging and effective fibre-coupling. Forhigh-speed data transmission up to hundreds of metres, 850-nmVCSELs are today the technology of choice. For higher bandwidthand longer distance networks, emission at long-wavelength(1.3-1.55 µm) is required. Long-wavelength VCSELs are,however, not available since no materials system offershigh-index-contrast distributed Bragg reflectors (DBRs) as wellas high-gain active regions at such wavelengths.High-performance DBRs may be built up from AlGaAs/GaAsmultilayers, but long wavelength quantum wells (QWs) are onlywell established in the InP system. Therefore, the bestperforming devices have relied on wafer-fusion betweenInP-based QWs and AlGaAs-DBRs. More recently, however, the mainefforts have been shifted towards all-epitaxial GaAs-baseddevices, employing 1.3-µm GaInNAs QWs.
In this thesis, different processing technologies forlong-wavelength VCSELs are described. This includes a thoroughinvestigation of wafer-fusion between InP and GaAs regardingelectro-optical as well as metallurgical properties, and thedevelopment of a stable low-pressure process for the selectiveoxidation of AlAs. Optimised AlGaAs/GaAs DBRs were designed andfabricated. An important and striking observation from thatstudy is that n-type doping potentially is much moredetrimental to device performance than previously anticipated.These investigations were exploited in the realisation of twonew VCSEL designs. Near-room-temperature continuous-waveoperation of a single-fused 1.55-µm VCSEL was obtained.This demonstrated the potential of InGaAsP/InP DBRs inhigh-performance VCSELs, but also revealed a high sensitivityto self-heating. Further efforts were therefore directedtowards all-epitaxial GaAs-based structures. This resulted in ahigh-performance 1215-nm VCSEL with a highly strained InGaAssingle QW. This can be viewed as a basis for longer-wavelengthVCSELs, i.e., with an emission wavelength approaching 1300 nm,either by an extensive device detuning or with GaInNAs QWs.
Keywords: VCSEL, vertical cavity laser, semiconductorlaser, long-wavelength, DBR, oxidation, wafer fusion, InGaAs,semiconductor processing
Place, publisher, year, edition, pages
Kista: Mikroelektronik och informationsteknik , 2001. , x, 62 p.
Trita-HMA, ISSN 1404-0379 ; 2001:6
VCSEL, vertical-cavity laser, semiconductor laser, long-wavelength, DBR, oxidation, wafer fusion, InGaAs, semiconductor processing
IdentifiersURN: urn:nbn:se:kth:diva-3258ISBN: ISSN 1404-0379OAI: oai:DiVA.org:kth-3258DiVA: diva2:9040
NR 201408052001-11-222001-11-22Bibliographically approved