InAs quantum dots with size fluctuations of less than 4% were grown on GaAs using the self-assembling method. By covering the quantum dots with In0.2Ga0.8As or In0.2Al0.8As, strain in InAs dots can be partly reduced due to relaxation of lattice constraint in the growth direction. This results in low-energy emission (about 1.3 μm) from the quantum dots. The photoluminescence linewidth can be reduced to 21 meV at room temperature. This width is completely comparable to the theoretical limit of a band-to-band emission from a quantum well at room temperature. Because the dots can be uniformly covered by the strain reducing layers, factors that degrade size uniformity during coverage, such as compositional mixing or segregation, will be suppressed, allowing for an almost ideal buried quantum dot structure.

A narrow photoluminescence linewidth of 21 meV at 1.35 μm from strain-reduced InAs quantum dots covered by In0.2Ga0.8As grown on GaAs substrates

http://nathan.instras.com/documentDB/paper-89.pdf

Photonic crystals in the optical regime — past, present and future

The lowest room-temperature threshold current density, 26 A/cm/sup 2/, of any semiconductor diode lasers is reported for a quantum dot device with a single InAs dot layer contained within a strained In/sub 0.15/Ga/sub 0.85/As quantum well. The lasers are epitaxially grown on a GaAs substrate, and the emission wavelength is 1.25 /spl mu/m.

Extremely low room-temperature threshold current density diode lasers using InAs dots in In0.15Ga0.85As quantum well

InAs self-organized quantum dots inserted in InGaAs quantum well have been grown on GaAs substrates by molecular beam epitaxy. The lateral size of the InAs islands has been found to be approximately 1.5 times larger as compared to the InAs/GaAs case, whereas the island heights and surface densities were close in both cases. The quantum dot emission wavelength can be controllably changed from 1.1 to 1.3 μm by varying the composition of the InGaAs quantum well matrix. Photoluminescence at 1.33 μm from vertical optical microcavities containing the InAs/InGaAs quantum dot array was demonstrated.

InAs/InGaAs quantum dot structures on GaAs substrates emitting at 1.3 μm

Concerns over possible toxicities of conventional metal-containing quantum dots have inspired growing research interests in colloidal silicon nanocrystals (SiNCs), or silicon quantum dots (SiQDs). This is related to their potential applications in a number of fields such as solar cells, optoelectronic devices and fluorescent bio-labelling agents. The past decade has seen significant progress in the understanding of fundamental physics and surface properties of silicon nanocrystals. Such understanding is based on the advances in the preparation and characterization of surface passivated colloidal silicon nanocrystals. In this critical review, we summarize recent advances in the methods of preparing high quality silicon nanocrystals and strategies for forming self-assembled monolayers (SAMs), with a focus on their bio-applications. We highlight some of the major challenges that remain, as well as lessons learnt when working with silicon nanocrystals (239 references).

/pdf/colloidal-silicon-quantum-dots-from-preparation-to-the-576g22lny4.pdf

Colloidal silicon quantum dots: from preparation to the modification of self-assembled monolayers (SAMs) for bio-applications

Room-temperature lasing at the wavelength of 1.31 μm is achieved from the ground state of an InGaAs/GaAs quantum-dot ensemble. At 79 K, a very low threshold current density of 11.5 A/cm2 is obtained at a wavelength of 1.23 μm. The room-temperature lasing at 1.31 μm is obtained with a threshold current density of 270 A/cm2 using high-reflectivity facet coatings. The temperature-dependent threshold with and without high-reflectivity end mirrors is studied, and ground-state lasing is obtained up to the highest temperature investigated of 324 K.

1.3 μm room-temperature GaAs-based quantum-dot laser

Data are presented on low threshold, 1.3-/spl mu/m oxide-confined InGaAs-GaAs quantum dot lasers. A very low continuous-wave threshold current of 1.2 mA with a threshold current density of 28 A/cm/sup 2/ is achieved with p-up mounting at room temperature. For slightly larger devices the continuous-wave threshold current density is as low as 19 A/cm/sup 2/.

Low-threshold oxide-confined 1.3-μm quantum-dot laser

Room-temperature continuous-wave operation of a 13 μm quantum dot laser is reported The threshold current for a single layer active region with p–up mounting is only 41 mA with a threshold current density of 45 A/cm2 The minimum room temperature threshold current density is 25 A/cm2 for pulsed operation Cryogenic and temperature dependent measurements are performed on broad-area lasers fabricated from the same active material At 4 K the broad-area threshold current density for uncoated facets is 6 A/cm2

Room-temperature continuous-wave operation of a single-layered 1.3 μm quantum dot laser

Data are presented on the temperature dependence of 1.3-/spl mu/m wavelength quantum-dot (QD) lasers. A low-threshold current density of 90 A/cm/sup 2/ is achieved at room temperature using high reflectivity coatings. Despite the low-threshold current density, lasing at the higher temperatures is limited by nonradiative recombination with a rapid increase in threshold current occurring above /spl sim/225 K. Our results suggest that very low threshold current density (/spl les/20 A/cm/sup 2/) can be achieved at room temperature from 1.3-/spl mu/m QD lasers, once nonradiative recombination is eliminated.

Temperature dependence of lasing characteristics for long-wavelength (1.3-μm) GaAs-based quantum-dot lasers

Data are presented on one- and two-stack InAs quantum dot lasers that have reduced temperature sensitivity of their lasing threshold. Adjustment of dot size and composition is used to increase the energy separation between the ground and first excited radiative transition energies to 104 meV, with a dot density of ∼3.1×1010 cm−2. The one- and two-stack lasers show broad area as-cleaved room temperature threshold current densities as low as 43 and 35 A/cm2, respectively. The wide energy separation between the ground and first excited radiative transitions leads to significant improvements in the temperature sensitivity of threshold.

G. Park

Papers

1.3 μm room-temperature GaAs-based quantum-dot laser

Low-threshold oxide-confined 1.3-μm quantum-dot laser

Room-temperature continuous-wave operation of a single-layered 1.3 μm quantum dot laser

Temperature dependence of lasing characteristics for long-wavelength (1.3-μm) GaAs-based quantum-dot lasers

Discrete energy level separation and the threshold temperature dependence of quantum dot lasers