MOVPE metamorphic lasers and nanostructures engineering at telecom wavelengths

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dc.contributor.advisor Pelucchi, Emanuele en
dc.contributor.advisor Townsend, Paul D. en
dc.contributor.advisor Povey, Ian en Mura, Enrica E. 2020-01-22T09:40:30Z 2019 2019
dc.identifier.citation Mura, E. 2019. MOVPE metamorphic lasers and nanostructures engineering at telecom wavelengths. PhD Thesis, University College Cork. en
dc.identifier.endpage 165 en
dc.description.abstract In recent years, considerable attention has been drawn to the design of heterostructures on GaAs substrates emitting in the 1.3-µm spectral range for replacing InP injection lasers in medium range fiber-optic communication links. Scaling considerations apart, the enhanced electronic confinement in GaAs-based devices can be expected to reduce carrier leakage at high temperatures, thereby overcoming one of the limiting factors associated with InP-based technologies. InGaAs metamorphic buffer heterostructures constitutes an alternative to the conventional routes relying on quantum dots or dilute nitride approaches, all with their own technical challenges and drawbacks. Metamorphic growth techniques provide compositionally graded buffer layers where the dislocations caused by strain relaxation are confined to the graded layers. However, when grown by metal-organic vapour phase epitaxy (MOVPE), it has been shown as extremely challenging to achieve ∼ 1.3µm emission in InGaAs metamorphic quantum well (QW) lasers (on GaAs substrate), due to a variety of strong, growth related issues, fundamentally linked to the overall epilayer thickness. In this contribution we demonstrate a > 1.3 µm-band laser grown by MOVPE on an engineered metamorphic parabolic graded InxGa1 –xAs buffer. A metamorphic multiple-quantum well structure containing cladding, active, and contact layers was grown. In the cladding, we exploit/control the correlation between epilayer thickness and defect generation and, importantly, demonstrate that the limiting factors introduced by surface instabilities during epitaxy can be managed by an innovative design. The bottom and the upper cladding are built as a combination of AlInGaAs and InGaP alloys in a superlattice (SL) structure. The improved quality of the material was confirmed, for example, by extensive Atomic Force Microscopy (AFM) analyses, showing low roughness (and no direct evidence of defect lines). The heavily compressive strain in QWs and in the metamorphic buffer layer (in combination with the surface step bunched ordering) promoted three-dimensional (3D) features formation under certain growth temperatures and for certain percentage of indium in the QWs. To avoid and control the 3D nanostructuring we proposed as a possible solution the insertion of a GaAs layer deposited before the QW. Moreover, we individuated a range of growth temperature and indium content in the QWs 3D-nanostructures and defects free, verifying the emission of interest. Building on these results, stripe waveguide lasers were fabricated, then characterized electro-optically. Best electro-optical result are reached with modified lower and upper SL cladding structures, adding a graded composition layers at the interfaces following the aim to improve the carrier transport. A 500 µm long and 2.5 µm wide stripe waveguide exhibited a threshold current (Ith) of ∼ 152 mA, corresponding to a density threshold current (Jth) of ∼ 127 mA/cm2 per QWs , operating at room temperature in pulse mode. The turning voltage was ∼ 0.8 V and the resistance series was 4.5 Ω. The emission wavelength was peaked at ∼ 1.34 µm, registered in pulse mode at low duty cycle. With shorter stripes laser, 10 µm and 20 µm wide, with different cavity lengths, we achieved the Light-current-voltage (L-I-V) curves in pulse and continuous wave (CW) mode. The threshold current varied from 130 mA to 170 mA in the operating temperature range of 30 ◦C-80 ◦C, and a characteristic temperature (T0) of 95 K was calculated. The internall loss (αi) and internal quantum efficiency (ηi) extrapolated were ∼ 30 cm−1 and ∼ 57% respectively. Those results prove that the epitaxial structure developed in this thesis work allow to fabricate one the few (specifically the second one, referring to that proposed by a Nippon Telegraph and Telephone Corporation (NTT) Japanese group in 2015 year) InGaAs metamorphic QW laser GaAs based, operating at > 1.3 µm using the MOVPE technology. en
dc.format.mimetype application/pdf en
dc.language.iso en en
dc.publisher University College Cork en
dc.rights © 2019, Enrica Mura. en
dc.rights.uri en
dc.subject InGaAs strained quantum wells en
dc.subject Metamorphic en
dc.subject Telecom lasers en
dc.subject Metal-organic vapour phase epitaxy en
dc.title MOVPE metamorphic lasers and nanostructures engineering at telecom wavelengths en
dc.type Doctoral thesis en
dc.type.qualificationlevel Doctoral en
dc.type.qualificationname PhD en
dc.internal.availability Full text available en
dc.description.version Accepted Version
dc.contributor.funder Irish Research Council en
dc.description.status Not peer reviewed en Physics en
dc.check.reason This thesis is due for publication or the author is actively seeking to publish this material en
dc.check.opt-out Not applicable en
dc.thesis.opt-out false
dc.check.entireThesis Entire Thesis Restricted
dc.check.embargoformat Apply the embargo to the e-thesis on CORA (If you have submitted an e-thesis and want to embargo it on CORA) en
dc.internal.conferring Spring 2020 en
dc.internal.ricu Tyndall National Institute en
dc.relation.project Irish Research Council (EPSPG/2014/35) en

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