We demonstrate quantum-dot (QD)-based, optically pumped semiconductor disk lasers (SDLs) for wavelengths ranging from 950 to 1210nm. QDs grown either in the submonolayer (SML) or in the Stranski–Krastanow (SK) regime are employed as active layers of the SDLs which are based on two different design concepts. Output power of up to 1.4W continuous wave (CW) is achieved with an InAs/GaAs-SML SDL at 1040nm. Up to 21 InGaAs SK-QD layers within a single SDL gain structure are used to realize the ground-state CW lasing with 0.3W at 1210nm. The SK-QD-based SDL shows temperature and pump-power stable emission. Threshold and differential efficiency do not depend on heat-sink temperature.

The high-frequency electrical properties of a vertical-cavity surface-emitting laser with a monolithically integrated electro-optical modulator are studied using small-signal modulation analysis of the electroreflectance. The experimental data obtained are approximated using the suggested equivalent electrical circuit, which accounts for the formation of a nonequilibrium space charge in the carrier-depletion region of the modulator. The bandwidth of the high-frequency electrical-signal transfer to the electro-optical region, determined for the suggested equivalent electrical circuit of the modulator, is shown to be 3GHz.

The buried oxide current-aperture in a pin diode-structure is used to create a strain field for the self-aligned nucleation of site-controlled single quantum dots. A single-photon source fabricated applying this approach shows spectrally very narrow emission lines (FWHM ≤ 25 μeV) and spectrally pure single-photon emission with a second-order autocorrelation g(2)(0) = 0.05.

Using cross-sectional scanning tunneling microscopy and photoluminescence spectroscopy, the atomic structure and optical properties of submonolayer depositions of InAs in GaAs are studied. The submonolayer depositions are formed by a cycled deposition of 0.5 monolayers InAs with GaAs spacer layers of different thicknesses between 1.5 and 32 monolayers. The microscopy images exhibit InAs-rich agglomerations with widths around 5 nm and heights of up to 8 monolayers. A lateral agglomeration density in the 1012 cm−2 range is found. During the capping of the InAs depositions a vertical segregation occurs, for which a segregation coefficient of ∼0.73 was determined. In the case of thin GaAs spacer layers, the observed segregation forms vertically connected agglomerations. The photoluminescence spectra exhibit peaks with linewidths below 10 meV and show a considerable dependence of the peak energy on the spacer thickness, even up to 32 monolayers GaAs, indicating a long range electronic coupling.

Time-resolved photoluminescence experiments on a coupled system of Stranski-Krastanov quantum dots (SK QDs) overgrown by a stack of submonolayer (SML) depositions reveal an acceleration of the carrier dynamics in the SML stack mediated by distance-dependent transfer processes. The coupling between an SML stack and an SK QD layer increases with decreasing spacer thickness $d$, which separates the two different nanostructure systems. This control parameter $d$ as well as the optical transition energies of the SML stack can be adjusted via the growth process. The observed photoluminescence dynamics of the combined SK QD and SML system is well described by a rate equation model which includes both pure zero-dimensional and zero-dimensional--two-dimensional states.

Semiconductor heterostructures represent the backbone for an increasing variety of electronic and photonic devices, for applications including information storage, communication and material treatment

Site-controlled growth of quantum dots (QDs) for single photon emitters (SPEs) is achieved applying a buried stressor approach. Theoretical and experimental analysis shows that site-controlled QD growth on buried oxide stressor-layers benefits enormously from a defect-free growth interface. Laterally modulated strain fields at GaAs(001) growth surfaces are used to tailor surface morphologies at the centre of prescribed mesa structures for subsequent QD growth. Suitable morphologies for site-controlled QD growth such as nano-hillocks and nanoholes are identified. Site-controlled QD growth appears above the boundaries between the oxidised layer and the non-oxidised semiconductor layer. Through fine tuning of wetting layer thickness and growth interruption high selectivity for QD nucleation is achieved. Thus, growth of single QDs at the centre of a current-injection limiting aperture is demonstrated. Moreover, the QD growth on a defect-free surface yields high quality optical properties in terms of narrow emission linewidth and temporal stability with no discernible difference to QDs grown on planar substrates. The technological simplicity of the buried stressor approach and the inherent integration of a current aperture for efficient carrier injection into site-selected QDs enable mass production of SPEs on large substrate sizes. (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Fundamentals of GaAs-based laser designs and the investigated (In)(Ga)As gain media concepts are discussed within this chapter. (Al)GaAs is the material system which is primarily employed for the infrared spectral range. Due to its versatility and ability to form dielectric mirrors for vertically emitting devices, (Al)GaAs forms the basis for a wide range of applications in the near infrared spectrum, and is well-established for industrial mass production.

Optical and electrical investigations of vertical-cavity surface-emitting lasers (VCSEL) with a monolithically integrated electro-optical modulator (EOM) allow for a detailed physical understanding of this complex compound cavity laser system. The EOM VCSEL light output is investigated to identify optimal working points. An electro-optic resonance feature triggered by the quantum confined Stark effect is used to modulate individual VCSEL modes by more than 20 dB with an extremely small EOM voltage change of less than 100 mV. Spectral mode analysis reveals modulation of higher order modes and very low wavelength chirp of < 0.5 nm. Dynamic experiments and simulation predict an intrinsic bandwidth of the EOM VCSEL exceeding 50 GHz.

This chapter discusses the influence of individual QD growth parameters and stacking challenges, along with the material quality and doping levels used for laser device growth. Long wavelength InGaAs QD growth process optimization for applications at $$1.3\,\upmu \mathrm{{m}}$$ is investigated. Notably, the role of the V/III ratio was found to be crucial for the long-term stability of QD properties during subsequent QD overgrowth and annealing. Results of MOVPE grown material properties used for device fabrication and limits of possible doping levels are outlined.

Electrical operation of single photon emitting devices employing site-controlled quantum dot (QD) growth is demonstrated. An oxide aperture acting as a buried stressor structure is forcing site-controlled QD growth, leading to both QD self-alignment with respect to the current path in vertical injection pin-diodes and narrow, jitter-free emission lines. Emissions from a neutral exciton, a neutral bi-exciton, and a charged exciton are unambiguously identified. Polarization-dependent measurements yield an exciton fine-structure splitting of (84 ± 2) μeV at photon energies of 1.28–1.29 eV. Single-photon emission is proven by Hanbury Brown and Twiss experiments yielding an anti-bunching value of g(2)(0) = 0.05 under direct current injection.

We present a “bottom-up” approach for the lateral alignment of semiconductor quantum dots (QDs) based on strain-driven self-organization. A buried stressor formed by partial oxidation of (Al,Ga)As layers is employed in order to create a locally varying strain field at a GaAs(001) growth surface. During subsequent strained layer growth, local self-organization of (In,Ga)As QDs is controlled by the contour shape of the stressor. Large vertical separation of the QD growth plane from the buried stressor interface of 150 nm is achieved enabling high optical quality of QDs. Optical characterization confirms narrow QD emission lines without spectral diffusion.

The atomic structure of multiple buried InAs depositions with a nominal thickness below one monolayer, separated by thin GaAs spacer layers, was investigated using Cs-corrected high-resolution transmission electron microscopy. InAs composition maps were obtained with sub-nanometer resolution by local evaluation of the {200}-Fourier coefficients of the lattice images. A strong segregation behavior of the InAs depositions is found, which leads to significant intermixing with the spacer layers. The segregation coefficient R≈0.7 is found to be independent of the spacer thickness, even for thin spacers with a thickness near the segregation length of about 3 monolayers.

Experimental results from the developed edge-emittin laser-diodes using the highly optimized new QD growth process are presented. Complete blue-shift suppression is achieved for long wavelength QDs. Stacks of QD layers emitting at $$1.3\,\upmu \mathrm{{m}}$$ are grown which show complete wavelength stability upon overgrowth or annealing at 615 $$^{\circ }$$ C and are used within a laser device.