QD lasers: physics and applications (original) (raw)
2005, Semiconductor and Organic Optoelectronic Materials and Devices
Quantum dot (QDs) heterostructures structurally represent tiny 3D insertions of a narrow bandgap material, coherently embedded in a wide-bandgap single-crystalline matrix. The QDs are produced by conventional epitaxial techniques applying self-organized growth and behave electronically as artificial atoms. Strain-induced attraction of QDs in different rows enables vertically-coupled structures for polarization, lifetime and wavelength control. Overgrowth with ternary or quaternary alloy materials allows controllable increase in the QD volume via the island-activated alloy phase separation. Repulsive forces during overgrowth of QDs by a matrix material enable selective capping of coherent QDs, keeping the defect regions uncapped for their subsequent selective evaporation. Low-threshold injection lasing is achieved up to 1350 nm wavelength at 300K using InAs-GaAs QDs. 8 mW VCSELs at 1.3 µm with doped DBRs are realized. Edge-emitters demonstrate 10 GHz bandwidth up to 70 o C without current adjustment. VCSELs show ~4 GHz relaxation oscillation frequency. QD lasers demonstrate above 3000 h of CW operation at 1.5 W at 45 o C heat sink temperature without degradation. The defect reduction technique (DRT) applied to thick layers enables realization of defect-free structures on top of dislocated templates. Using of DRT metamorphic buffer layers allowed 7W GaAs-based QD lasers at 1500 nm.
Sign up for access to the world's latest research.
checkGet notified about relevant papers
checkSave papers to use in your research
checkJoin the discussion with peers
checkTrack your impact
Related papers
QD lasers: physics and applications
Storage and Retrieval for Image and Video Databases, 2005
Quantum dot (QDs) heterostructures structurally represent tiny 3D insertions of a narrow bandgap material, coherently embedded in a wide-bandgap single-crystalline matrix. The QDs are produced by conventional epitaxial techniques applying self-organized growth and behave electronically as artificial atoms. Strain-induced attraction of QDs in different rows enables vertically-coupled structures for polarization, lifetime and wavelength control. Overgrowth with ternary or quaternary alloy
Quantum dot lasers: breakthrough in optoelectronics
Thin Solid Films, 2000
Semiconductor heterostructures with self-organized quantum dots (QDs) have experimentally exhibited properties expected for zerodimensional systems. When used as active layer in the injection lasers, these advantages help to strongly increase material gain and differential gain, to improve temperature stability of the threshold current, and to provide improved dynamic properties. Molecular beam epitaxy (MBE) represents a developed technology well suited for fabrication of self-organized QDs. Optimization of deposition parameters can ensure that the self-organized islands are small (,10 nm), have a similar size and shape and form dense arrays. Saturation material gain is as high as 150000 cm 21 compared with QW values of about 3000 cm 21. Maximum differential gain reported for QD lasers approaches 10 212 cm 2 and exceeds the QW laser values by about three orders of magnitude. Direct observation of relaxation oscillations reveals present cutoff frequencies close to 10 GHz. High internal (.96%) and differential (70%) ef®ciencies at 300 K are realized. Using the novel concept of electronically-coupled QDs and oxide-de®ned 10 mm apertures, CW lasing with J th 180 A/cm 2 , is realized in surface-emitting QD lasers (300 K). Wall-plug ef®ciencies are up to 16%. Total currents as low as 68 mA are measured for 1mm apertures. GaAs-based lasers for the 1.3 mm range with low J th (65 A/cm 2) at room temperature (RT) are realized using InAs/InGaAs/GaAs QDs obtained by activated spinodal decomposition. In stripes the lasing occurs via the QD ground state (J th 90 A/cm 2) for cavity lengths L. 1 mm (uncoated). Differential ef®ciency is 55% and internal losses are 1.5 cm 21. A characteristic temperature near RT is 160 K. 3W CW operation at RT is achieved. The recent progress in lasers based on self-organized MBE QDs already made it possible to fabricate devices with dramatically improved characteristics as compared to recent QW devices for the most important commercial applications.
Novel In-Plane Semiconductor Lasers V, 2006
We have performed a systematic study of structural and optical properties of Quantum dot (QDs) lasers based on InAs/InGaAs quantum dots grown on GaAs substrates emitting in the 1.3 -1.5 µm range. 1.3 µm range QD lasers are grown using GaAs as matrix material. It is shown that the lasers, grown with large number of QD stacks are metamorphic, with plastic relaxation occurring through the formation of misfit dislocations. Thus, 1.3 µm QD lasers with large number of stacks grown without strain compensation are metamorphic. Another type of defects is related to local dislocated clusters, which are the most dangerous. When proper optimization of the growth conditions is carried out, including a selective thermal etching off of statistically formed dislocated clusters through the defect-reduction technique (DRT), no significant impact of misfit dislocations on the degradation robustness is observed. In uncoated devices a high cw single mode power of ~700 mW is realized limited by thermal roll-over, which is not affected by 500 h ageing at room temperature. At elevated temperatures the main degradation mechanism revealed is catastrophic optical mirror damage (COMD). When the facet are passivated, the devices show the extrapolated operation lifetime in excess of 10 6 h at 40 o C at ~100 mW cw single mode output power. Longer wavelength (1.4 -1.5 µm) devices are grown on metamorphic (In,Ga,Al)As layers deposited on GaAs substrates. In this case, the plastic relaxation occurs through formation of both misfit and threading dislocations. The latter kill the device performance. Using DRT in this case enables blocking of threading dislocation with growth of QDs in defect-free upper layers. DRT is realized by selective capping of the defect-free areas and high-temperature etching of nano-holes at the non-capped regions near the dislocation. The procedure results in etching of holes and is followed by fast lateral overgrowth with merger of the growth fronts. If the defect does not propagate into the upper layer when the hole is capped, the upper layers become defect-free. Lasers based on this approach exhibited emission wavelength in the 1.4 -1.5 µm range with a differential quantum efficiency of about ~50%. The narrow-stripe lasers operate in a single transverse mode and withstand continuous current density above 20 kA cm -2 without degradation. A maximum continuous-wave output power of 220 mW limited by thermal roll-over is obtained. No beam filamentation was observed up to the highest pumping levels. Narrow stripe devices with as-cleaved facets are tested for 60 o C (800 h) and 70 o C (200 h) on-chip temperature. No noticeable degradation has been observed at 50 mW cw single mode output power. This shows the possibility of degradation-robust devices on foreign substrates. The technology opens a way for integration of various III-V materials and may target degradation-free lasers on silicon for further convergence of computing and communications.
We have performed a systematic study of structural and optical properties of Quantum dot (QDs) lasers based on InAs/InGaAs quantum dots grown on GaAs substrates emitting in the 1.3 – 1.5 µm range. 1.3 µm range QD lasers are grown using GaAs as matrix material. It is shown that the lasers, grown with large number of QD stacks are metamorphic, with plastic relaxation occurring through the formation of misfit dislocations. Thus, 1.3 µm QD lasers with large number of stacks grown without strain compensation are metamorphic. Another type of defects is related to local dislocated clusters, which are the most dangerous. When proper optimization of the growth conditions is carried out, including a selective thermal etching off of statistically formed dislocated clusters through the defect-reduction technique (DRT), no significant impact of misfit dislocations on the degradation robustness is observed. In uncoated devices a high cw single mode power of ~700 mW is realized limited by thermal ...
Epitaxial growth of quantum-dot heterostructures on metamorphic buffers
2005
Recent achievements in self-organized quantum dots (QDs) have demonstrated their potential for long-wavelength laser applications. However, the wavelength of QD structures pseudomorphically grown on GaAs substrate is typically not longer than 1 .3 tm. In this work we study a novel approach for extension of the spectral range of GaAs-based diode lasers up to 1.5 jtm. We use a sensitivity of QD emission to the band gap energy of surrounding matrix. The method is based on formation of a QD array inside a metamorphic InGaAs epilayer. Growth regimes of metamorphic buffer that enable mirror-like surface morphology in combination with effective dislocation trapping are discussed. Structural and optical properties of metamorphic InAs/InGaAs QDs are presented. It is shown that the wavelength of QD emission can be controllably tuned in the 1.37-1.58 tm range by varying the composition of metamorphic InGaAs matrix. Details of formation, fabrication, and characterization of metamorphic-based diode lasers are also presented. We demonstrate a lasing wavelength as long as 1.48 jtm in the 20-80 °C temperature interval. The minimum threshold current density is 800 A/cm2 at RT. The external differential efficiency and pulsed power maximum exceed 50%and 7 W, respectively.
Nano-engineering approaches to self-assembled InAs quantum dot laser medium
Journal of Electronic Materials, 2006
An umber of nano-engineering methods are proposed and tested to improve optical properties of alaser gain medium using the self-assembled InAs quantum dot (QD) ensemble. The laser characteristics of concerni nclude higher gain, larger modulation bandwidth, highere fficiency at elevated temperatures,h ighert hermal stability, and enhanced reliability. The focus of this paper is on the management of QD properties throughd esign and molecular beam epitaxial growth and modification of QD heterostructures.This includes digital alloysa sh igh-quality wide-bandgap barrier;u nder-and overlayers with various compositions to control thed ynamics of QD formation and evolution on the surface; shape engineering of QDs to improve electron-hole overlapa nd reduce inhomogeneous broadening; band engineering of QD heterostructures to enhance the carrierl ocalization by reduction of thermal escapef rom dots; as well as tunnel injection from quantum wells( QWs) to accelerate carriert ransfer to the lasing state. Beneficial properties of the developedQ Dm edia are demonstrated at room temperature in laser diodes with unsurpassedthermal stabilitywithacharacteristic temperatureof380 K, high waveguide modal gain . 50 cm ÿ 1 ,u nsurpassed defect toleranceo vert wo orderso fm agnitude highert han that of QWs typically used in lasers, and efficient emission from at wo-dimensional (2-D)p hotonic crystal nanocavity.
Semiconductor quantum dots for application in diode lasers
Thin Solid Films, 1998
. Recent progress in the epitaxy molecular beam epitaxy and metal-organic chemical vapor deposition of strained heterostructures and the use of the Stranski-Krastanow growth mode allows to create spontaneously ordered, defect-free and dense arrays of nano-size islands. Such islands act as electronic quantum dots. In superlattices the islands are ordered in vertical stacks. Using such self-ordered InGaAsrAlGaAs quantum dots we have fabricated diode lasers for which some properties are superior to those of current lasers based on quantum wells. In particular, we have demonstrated low laser threshold current and high temperature stability of the threshold. q 1998 Elsevier Science S.A.
Loading Preview
Sorry, preview is currently unavailable. You can download the paper by clicking the button above.