Optoelectronic properties of InAs GaAs columnar quantum dot laser diodes

In this thesis results are described with the aim of examining the optoelectronic properties of InAs/GaAs columnar quantum-dots and comparing them with those of more conventional self-assembled quantum-dots. The polarisation properties of a set of columnar quantum-dot samples — of varied aspect ratio and In compositional contrast between the rod-shaped dot and the surrounding 2-D layer — are studied. For this investigation a new method to obtain the ratio of the fundamental TE/TM optical response using edge photo-absorption spectroscopy is proposed, which corrects for the polarisation-dependent features of the experimental set-up. The method is verified by application to compressive and tensile strained InGaP quantum well structures, where the results are in agreement with known ratios of the band-edge matrix elements. When applied to columnar quantum-dot samples it is shown that the TE/TM optical response depends on the dot aspect ratio and the In compositional contrast. A polarisation-independent photo-absorption is illustrated for a columnar quantum-dot of an aspect ratio (dot's height over diameter) 3.51:1, which is desired for use in semiconductor optical amplifiers. For the columnar dot of an extremely high aspect ratio, 7.5:1, a room temperature TM-dominant polarisation lasing emission is observed. By studying the Quantum-Confined Stark Effect, a dramatic enhancement of the Stark shift amplitude is shown for columnar quantum-dot samples of an increased dot aspect ratio from 0.63:1 up to 1.12:1, which may have application in optical modulation/switching. For a higher aspect ratio columnar quantum-dot the shift of the band edge of the photo-absorption spectra is reduced dramatically and this has been attributed to an overall effect where the observable shift becomes the result of higher energy transitions, where their oscillator strength change very rapidly within the studied range of field. For the highest aspect ratio dot, i.e. of aspect ratio 10:1, there is no any observable shift.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Optoelectronic properties of InAs GaAs columnar quantum dot laser diodes

In this thesis results are described with the aim of examining the optoelectronic properties of InAs/GaAs columnar quantum-dots and comparing them with those of more conventional self-assembled quantum-dots. The polarisation properties of a set of columnar quantum-dot samples — of varied aspect ratio and In compositional contrast between the rod-shaped dot and the surrounding 2-D layer — are studied. For this investigation a new method to obtain the ratio of the fundamental TE/TM optical response using edge photo-absorption spectroscopy is proposed, which corrects for the polarisation-dependent features of the experimental set-up. The method is verified by application to compressive and tensile strained InGaP quantum well structures, where the results are in agreement with known ratios of the band-edge matrix elements. When applied to columnar quantum-dot samples it is shown that the TE/TM optical response depends on the dot aspect ratio and the In compositional contrast. A polarisation-independent photo-absorption is illustrated for a columnar quantum-dot of an aspect ratio (dot's height over diameter) 3.51:1, which is desired for use in semiconductor optical amplifiers. For the columnar dot of an extremely high aspect ratio, 7.5:1, a room temperature TM-dominant polarisation lasing emission is observed. By studying the Quantum-Confined Stark Effect, a dramatic enhancement of the Stark shift amplitude is shown for columnar quantum-dot samples of an increased dot aspect ratio from 0.63:1 up to 1.12:1, which may have application in optical modulation/switching. For a higher aspect ratio columnar quantum-dot the shift of the band edge of the photo-absorption spectra is reduced dramatically and this has been attributed to an overall effect where the observable shift becomes the result of higher energy transitions, where their oscillator strength change very rapidly within the studied range of field. For the highest aspect ratio dot, i.e. of aspect ratio 10:1, there is no any observable shift

High quality factor nitride-based optical cavities: microdisks with embedded GaN/Al(Ga)N quantum dots

We compare the quality factor values of the whispery gallery modes of microdisks incorporating GaN quantum dots (QDs) grown on AlN and AlGaN barriers by performing room temperature photoluminescence (PL) spectroscopy. The PL measurements show a large number of high Q factor (Q) resonant modes on the whole spectrum which allows us to identify the different radial mode families and to compare them with simulations. We report a considerable improvement of the Q factor which reflect the etching quality and the relatively low cavity loss by inserting QDs into the cavity. GaN/AlN QDs based microdisks show very high Q values (Q > 7000) whereas the Q factor is only up to 2000 in microdisks embedding QDs grown on AlGaN barrier layer. We attribute this difference to the lower absorption below bandgap for AlN barrier layers at the energies of our experimental investigation

Polarization dependence study of electroluminescence and absorption from InAs / GaAs columnar quantum dots

Semiconductor optical amplifiers based on InGaAs columnar quantum dots (CQDs) with different numbers of superlattice periods were fabricated and tested. The polarization dependence of the electroluminescence(EL) and absorption of such CQDs structures were measured. Compared to standard QDs a large improvement in the ratio of transverse-magnetic (TM) and -electric (TE) integrated EL was obtained in CQDs, depending on the number of stacked GaAs / InAs superlattice periods, which can be attributed to the more symmetric shape of CQDs. TM and TE resolved photovoltage absorption spectroscopy confirmed this improvement. A small spectral separation between TE- and TM-EL peaks has been observed showing that heavy and light holelike states are energetically close in these QDs

Polarization response of quantum-confined structures using edge-photovoltage spectroscopy

We propose a method to obtain the ratio of the fundamental TE/TM optical response of a quantum-confined system from the measurement of the polarization dependence of the edge photovoltage spectrum by correcting for polarization-dependent features of the experimental system. When applied to compressive- and tensile-strained InGaP quantum well structures, the results are in excellent agreement with known ratios of the band-edge matrix elements. The method will be of a particular value in the study of quantum dot systems

Towards polarization insensitive semiconductor optical amplifiers using InAs/GaAs columnar quantum dots

We report columnax quantum dots (CQDs) with extremely large aspect ratios, showing nearly polarization-insensitive electroluminescence. A systematic experimental and theoretical investigation of their polarization properties as a function of aspect ratio is also reported. (c) 2008 Optical Society of Americ

Nitride nanophotonics from the deep ultra-violet to the near infrared: non-linear optics and microlasers

International audienceThe recent developments of nitride nanophotonics, based on photonic crystal membrane nanocavities and microdisk resonators, pave the way to a novel nanophotonic platform. Here we present two recent achievements: first we demonstrate the room-temperature operation of a nitride microlaser emitting in the deep UV spectral range (=275 nm) with GaN/AlN multiple quantum wells. Secondly we tailor the second-harmonic generation of a cw near infra-red radiation coupled to a high quality factor photonic crystal cavity

A nitride-on-Silicon microdisk laser emitting at 275 nm and room-temperature

International audienceThe development of semiconductor lasers in the deep ultra-violet (UV) spectral range is attracting a strong interest, related to their multiple applications for optical storage, biochemistry or optical interconnects. UV-emitting ridge lasers usually embed nitride heterostructures grown on complex buffer layers or expensive substrates – an approach that cannot be extended to nano-photonics and microlasers. We demonstrate here the first deep UV microlaser by combining binary GaN/AlN thin quantum wells (QWs) grown on a silicon substrate and high quality factor microdisk resonators. Those microdisk lasers operate at 275nm at room temperature under optical pumping.The nitride heterostructures grown on silicon present a strong interest for nanophotonic devices emitting in the blue and UV range. The etching selectivity of the silicon substrate allows to realize free membrane photonic structures with high quality factors (Q) [1-3]. In the present microdisk resonators, the electromagnetic modes, the so-called Whispering-Gallery Modes (WGMs), present a low modal volume and Q factors of 6000 [4]. The difficulty in extending their lasing operation in the UV range mainly lies in the control of the active layer. Low defect density quantum wells grown on thick buffer layers or nitride substrates are usually employed for ridge lasers. Here we show that binary GaN/AlN ultra-thin quantum wells directly grown on a silicon substrate can maintain a large emission efficiency and lead to lasing at room temperature (Figure 1). This active layer can form free-standing membranes and is further compatible with future developments of nitride nanophotonic platforms on silicon