Long wavelength lasers and semiconductor optical amplifiers based on InAs quantum wire-/dot-like active regions were developed on InP substrates dedicated to cover the extended telecommunication wavelength range between 1.4 and 1.65 µm. In a brief overview different technological approaches will be discussed, while in the main part the current status and recent results of quantum-dash lasers are reported. This includes topics like dash formation and material growth, device performance of lasers and optical amplifiers, static and dynamic properties and fundamental material and device modelling.

We report measured evolutions of the optical band gap, refractive index, and relative dielectric constant of TiO2 film obtained by electron beam gun evaporation and annealed in an oxygen environment. A negative shift of the flat band voltage with increasing annealing temperatures, for any film thickness, is observed. A dramatic reduction of the leakage current by about four orders of magnitude to 5×10−6 A/cm2 (at 1 MV/cm) after 700 °C and 60 min annealing is found for films thinner than 15 nm. An equivalent SiO2 thickness of the order of 3–3.5 nm is demonstrated. An approach is presented to establish that at different ranges of applied voltage the hopping, space charge limited current, and Fowler–Nordheim are the basic mechanisms of carrier transport into the TiO2 film.

We describe a theoretical model for the linear optical gain properties of a quantum wire assembly and compare it to the well known case of a quantum dot assembly. We also present a technique to analyze the gain of an optical amplifier using bias dependent room temperature amplified spontaneous emission spectra. Employing this procedure in conjunction with the theoretical gain model, we demonstrate that InAs/InP quantum dash structures have quantum-wire-like characteristics. The procedure was used to extract the net gain coefficient, the differential gain, and the relative current component contributing to radiative recombination.

We present a detailed study of the evolution with annealing temperature (in an oxygen environment) of the morphological and structural properties of thin erbium oxide (Er2O3) films evaporated in an electron beam gun system. The electrical characteristics of metal-oxide-semiconductor structures are also described. Atomic force microscope and x-ray difractometry were used to map out the morphology and crystalline nature of films ranging in thickness from 4.5 to 100 nm. High-resolution cross-sectional transmission electron microscopy imaging and Auger electron spectroscopy reveal three sublayers: an outer dense nanocrystalline Er2O3 layer, a middle transition layer and amorphous SiO2 film placed close to the Si substrate. The effective dielectric constant depends on the thickness and the annealing temperature. A 1–2.8 nm interfacial SiO2 layer as well as an ErO inclusion with low polarizability are formed during the deposition and the annealing process has a profound effect on the dielectric constant and the leakages. The minimum effective oxide thickness is 2.4–2.8 nm and in the thinnest films we obtained a leakage current density as low as 1–5×10−8 A/cm2 at an electric field of 1 MV/cm. We observe a shift of the flatband voltage to the positive side and significant lowering of the positive charge down to ∼1×1010 cm−2. For a 4.5 nm film, the maximum total breakdown electric field was approximately 1×107 V/cm.

We report properties of Er2O3 films deposited on silicon using electron-beam gun evaporation. We describe the evolution with thickness and annealing temperature of the morphology, structure, and electrical characteristics. An effective relative dielectric constant in the range of 6–14, a minimum leakage current density of 1–2×10−8 A/cm2 at an electric field of 106 V/cm and breakdown electric field of 0.8–1.7×107 V/cm are demonstrated. Breakdown electric field and leakage current densities are correlated with the surface morphology. The obtained characteristics make the Er2O3 films a promising substitute for SiO2 as an ultrathin gate dielectric.

Structural properties of an ultrathin, 4.5 nm, erbium-oxide film and electrical properties of metal–oxide–semiconductor structure based on it are described. The evolution of the dielectric constant, total charge density, breakdown electric field, and leakage current density with annealing temperature in an oxygen environment are reported. The dielectric constant in the as-deposited state is relatively low, ∼7, possibly because the initial deposition forms ErO (with low polarizibility) rather than Er2O3. Annealing causes a transformation of ErO to Er2O3 but at the same time it initiates the growth of an interfacial SiO2 layer so that the effective dielectric constant is reduced to 5.5. Using the 4.5 nm film following annealing at up to 750 °C, we demonstrate an effective oxide thickness in the range 2.4–3.2 nm, with a leakage current density as low as 1–2×10−8 A/cm2 at an electric field of 106 V/cm and a breakdown electric field of 0.8–1.7×107 V/cm. A shift of the flat band voltage to the positive side and lowering of the total positive charge density down to 1012 cm−2 with annealing temperature are observed and can be explained by a charge compensation mechanism between the charges accumulated at the SiO2/Er2O3 and Si/SiO2 interface.

The dynamic properties of ground- and excited-state emission in InAs/GaAs quantum-dot lasers operating close to 1.31 μm are studied systematically. Under low bias conditions, such devices emit on the ground state, and switch to emission from the excited state under large drive currents. Modification of one facet reflectivity by deposition of a dichroic mirror yields emission at one of the two quantum-dot states under all bias conditions and enables to properly compare the dynamic properties of lasing from the two different initial states. The larger differential gain of the excited state, which follows from its larger degeneracy, as well as its somewhat smaller nonlinear gain compression results in largely improved modulation capabilities. We demonstrate maximum small-signal bandwidths of 10.51 GHz and 16.25 GHz for the ground and excited state, respectively, and correspondingly, large-signal digital modulation capabilities of 15 Gb/s and 22.5 Gb/s. For the excited state, the maximum error-free bit rate is 25 Gb/s.

No abstract