Showing papers in "Semiconductor Science and Technology in 2005"

Transparent conducting oxide semiconductors for transparent electrodes

Abstract: The present status and prospects for further development of polycrystalline or amorphous transparent conducting oxide (TCO) semiconductors used for practical thin-film transparent electrode applications are presented in this paper. The important TCO semiconductors are impurity-doped ZnO, In2O3 and SnO2 as well as multicomponent oxides consisting of combinations of ZnO, In2O3 and SnO2, including some ternary compounds existing in their systems. Development of these and other TCO semiconductors is important because the expanding need for transparent electrodes for optoelectronic device applications is jeopardizing the availability of indium-tin-oxide (ITO), whose main constituent, indium, is a very expensive and scarce material. Al- and Ga-doped ZnO (AZO and GZO) semiconductors are promising as alternatives to ITO for thin-film transparent electrode applications. In particular, AZO thin films, with a low resistivity of the order of 10−5 Ω cm and source materials that are inexpensive and non-toxic, are the best candidates. However, further development of the deposition techniques, such as magnetron sputtering or vacuum arc plasma evaporation, as well as of the targets is required to enable the preparation of AZO and GZO films on large area substrates with a high deposition rate.

THz imaging and sensing for security applications—explosives, weapons and drugs

Abstract: Over the past 5 years, there has been a significant interest in employing terahertz (THz) technology, spectroscopy and imaging for security applications. There are three prime motivations for this interest: (a) THz radiation can detect concealed weapons since many non-metallic, non-polar materials are transparent to THz radiation; (b) target compounds such as explosives and illicit drugs have characteristic THz spectra that can be used to identify these compounds and (c) THz radiation poses no health risk for scanning of people. In this paper, stand-off interferometric imaging and sensing for the detection of explosives, weapons and drugs is emphasized. Future prospects of THz technology are discussed.

ZnO nanorods: synthesis, characterization and applications

Abstract: This paper presents a review of current research activities on ZnO nanorods (or nanowires). We begin this paper with a variety of physical and chemical methods that have been used to synthesize ZnO nanorods (or nanowires). There follows a discussion of techniques for fabricating aligned arrays, heterostructures and doping of ZnO nanorods. At the end of this paper, we discuss a wide range of interesting properties such as luminescence, field emission, gas sensing and electron transport, associated with ZnO nanorods, as well as various intriguing applications. We conclude with personal remarks on the outlook for research on ZnO nanorods.

Growth of 2 inch ZnO bulk single crystal by the hydrothermal method

Abstract: Zinc oxide (ZnO) single crystals were grown by the hydrothermal method using a platinum inner container. The 2 inch ZnO wafers obtained from these bulk crystals possess an extremely high crystallinity and purity. The electrical resistivity is highly uniform over the entire wafer area. After annealing, the step-and-terrace structure was observed on the surface of the wafer. The etch pit density was decreased to less than 80 cm−2. These results suggest that these 2 inch ZnO wafers are suitable for wide band gap device applications.

Chemical recognition in terahertz time-domain spectroscopy and imaging

Abstract: In this paper, we present an overview of chemical recognition with ultrashort THz pulses. We describe the experimental technique and demonstrate how signals for chemical recognition of substances in sealed containers can be obtained, based on the broadband absorption spectra of the substances. We then discuss chemical recognition in combination with THz imaging and show that certain groups of biological substances may give rise to characteristic recognition signals. Finally, we explore the power of numerical prediction of absorption spectra of molecular crystals and illuminate some of the challenges facing state-of-the-art computational chemistry software.

Erbium in silicon

Abstract: The overlap of the principal luminescence band of the erbium ion with the low-loss optical transmission window of silica optical fibres, along with the drive for integration of photonics and silicon technology, has generated intense interest in doping silicon with erbium to produce a silicon-based optical source Silicon is a poor photonic material due to its very short non-radiative lifetime and indirect band gap, but it has been hoped that the incorporation of optically active erbium ions into silicon will permit the development of silicon-based light sources that will interface with both CMOS technology and optical fibre communications Some years into this activity, there have now been a wide range of experimental studies of material growth techniques, optical, physical and electrical properties, along with a considerable body of theoretical work dealing with the site of the erbium ion in silicon, along with activation and deactivation processes This paper reviews the current state of what remains an active field, summarizing results from a range of studies conducted over the last few years, and points to further developments by considering the prospects for successful photonic integration of erbium and silicon

Electrical and optical properties of p-type ZnO

Abstract: ZnO has ideal qualities for bright, efficient UV light emitting diodes and laser diodes, based on p–n junctions. However, while high quality n-type ZnO has been available for many years, the development of good p-type material is a much more recent phenomenon. The most successful acceptor dopants have been the group V elements, N, P and As; N substitutes on the O site, but the exact structures of the P and As acceptors have not yet been established. Resistivities as low as 0.4 Ω cm have been measured, and some UV heterojunction and homojunction LEDs have been fabricated. Optical fingerprints of p-type ZnO often include a photoluminescence line at 3.31 eV, and strong donor-bound exciton lines at 3.357 and 3.367 eV, both of which are well known from previous studies of n-type ZnO.

Annealing effects on the properties of copper oxide thin films prepared by chemical deposition

Abstract: We have investigated the annealing effect on the structural, optical and electrical properties of copper oxide films prepared on glass substrates by chemical deposition. The films were annealed in air for different temperatures ranging from 200 to 350 °C. X-ray diffraction patterns showed that the films as-deposited and annealed at 200 and 250 °C are of cuprite structure with composition Cu2O. Annealing at 300 °C converts these films to CuO. This conversion is accompanied by a shift in the optical band gap from 2.20 eV to 1.35 eV. Also this conversion was obtained by the dc electrical conductivity and FTIR spectroscopy measurements.

Comparison between pulsed terahertz time-domain imaging and continuous wave terahertz imaging

Abstract: We report an evaluation of pulsed terahertz (THz) time-domain measurement and continuous wave (CW) terahertz measurement for non-destructive testing applications. The strengths and limitations of the modalities are explored via the example of the detection of defects in space shuttle foam insulation. It is decided that CW imaging allows for a more compact and simple system, while pulsed measurements yield a broader range of information.

Pulsed laser deposition of thin films and superlattices based on ZnO

Abstract: The pulsed laser deposition (PLD) technique has been applied for the epitaxial growth of ZnO for more than two decades. The emergence of high-temperature stability of the excitonic lasing was first demonstrated in a microcrystalline ZnO film grown by PLD leading to recent remarkable growth in this field. A number of attempts have been made to improve the crystallinity for realizing p-type materials in the quest for ZnO-based short wavelength light emitting devices (LEDs). In this paper, we describe practical advantages of PLD and currently accomplished intrinsic properties of ZnO films according to the abundant literature. We find that correlation between Hall mobility and lateral grain size captures the effect of grain boundaries for the films grown on sapphire substrates. On the other hand, advantages of the use of lattice-matched ScAlMgO4 substrate are evidenced by the lower residual electron density, higher mobility and sharper exciton peaks in the photoluminescence and absorption spectra. We also focus on the wide-band-gap ternary alloy, MgxZn1−xO, especially in terms of the composition dependence of its lattice parameters and band-gap in two different crystallographic phases, to discuss the stability of this metastable compound. The studies on the PLD growth of multilayer and superlattices are briefly reviewed. We finally present the current capability of electron and hole doping by incorporating Ga and N into films grown on (0001) ScAlMgO4 substrates. We conclude that the PLD technique and related technologies have now mature to meet the requirements for fabricating UV-LEDs.

Magnetic oxide semiconductors

Abstract: Magnetic oxide semiconductors, oxide semiconductors doped with transition metal elements, are one of the candidates for a high Curie temperature ferromagnetic semiconductor that is important to realize semiconductor spintronics at room temperature. We review in this paper recent progress of research on various magnetic oxide semiconductors. The magnetization, magneto-optical effect and magneto-transport such as the anomalous Hall effect are examined from the viewpoint of feasibility to evaluate the ferromagnetism. The ferromagnetism of Co-doped TiO2 and transition metal-doped ZnO is discussed.

Band gap shift, structural characterization and phase transformation of CdSe thin films from nanocrystalline cubic to nanorod hexagonal on air annealing

Abstract: Cadmium selenide (CdSe) thin films were deposited on a glass substrate using the chemical bath deposition method at room temperature. The films were deposited using cadmium acetate as a Cd2+ ion source and sodium selenosulfate as a Se2? ion source. The 'as-deposited' CdSe thin films are red in colour and specularly reflective. The 'as-deposited' CdSe layers grew with nanocrystalline cubic phase along with some amorphous phase present, with an optical band gap 'Eg' of 2.3 eV and electrical resistivity of the order of 105?106 ? cm. The 'as-deposited' film is annealed in air at 673 K for 4 h and the effect of annealing on structural, morphological, optical and electrical properties is studied. It is worth noting that after annealing, metastable nanocrystallite cubic phase transforms into stable well crystalline hexagonal phase and films show a 'redshift' of '0.6 eV' in their optical band gap 'Eg'. After annealing, the crystallites' size increases from 45 ? to 180 ?, which results in a decrease in electrical resistivity. These changes have been attributed to the crystallite size dependent properties of CdSe semiconductor thin films.

Optical properties of excitons in ZnO-based quantum well heterostructures

Abstract: Recently the developments in the field of II?VI-oxides have been spectacular. Various epitaxial methods have been used to grow epitaxial ZnO layers. Not only epilayers but also sufficiently good-quality multiple quantum wells (MQWs) have been grown by laser molecular-beam epitaxy (laser-MBE). We mainly discuss the experimental aspect of the optical properties of excitons in ZnO-based MQW heterostructures. Systematic temperature-dependent studies of optical absorption and photoluminescence in these MQWs were used to evaluate the well-width dependence and the composition dependence of the major excitonic properties. Based on these data, the localization of excitons, the influence of exciton?phonon interaction and quantum-confined Stark effects are discussed. The optical spectra of dense excitonic systems are shown to be determined mainly by the interaction process between excitons and biexcitons. The high-density excitonic effects play a role in the observation of room-temperature stimulated emission in the ZnO MQWs. The binding energies of exciton and biexciton are enhanced from the bulk values, as a result of quantum-confinement effects.

Continuous THz-wave generation using antenna-integrated uni-travelling-carrier photodiodes

Abstract: Photonic generation of continuous millimetre- and sub-millimetre waves up to the THz range using antenna-integrated uni-travelling-carrier photodiodes is described. A device integrating a wideband log-periodic antenna exhibits a maximum output power of 2.6 ?W at 1.04 THz with good linearity. A module with a quasi-optical output port fabricated for practical use generates almost the same output power as the chip at around 1 THz and operates at frequencies of up to 1.5 THz. The output power level and the operation frequency are records for wideband photodiodes operating at 1.55 ?m. Devices integrating resonant narrowband dipole antennae have also been fabricated and the output power increases at resonant peak frequencies confirmed. The device having a peak at 1.04 THz exhibits a maximum (detected) output power of 10.9??W at 1.04 THz with good linearity. This output power is the highest value ever directly generated from a photodiode in the THz range, and several times higher than the maximum value reported by the low-temperature-grown GaAs photoconductive switch at around 1 THz.

High power temperature-insensitive 1.3 µm InAs/InGaAs/GaAs quantum dot lasers

Abstract: We report on GaAs-based broad area (100 µm) 1.3 µm quantum dot (QD) lasers with high CW output power (5 W) and wall-plug efficiency (56%). The reliability of the devices has been demonstrated beyond 3000 h of CW operation at 0.9 W and 40 °C heat sink temperature with 2% degradation in performance. P-doped QD lasers with a temperature-insensitive threshold current (T0 > 650 K) and differential efficiency (T1 = infinity) up to 80 °C have been realized.

On the properties of indium doped ZnO thin films

Abstract: Thin films of undoped and In-doped zinc oxide, prepared using chemical spray pyrolysis, were investigated using x-ray diffraction, optical transmission and absorption spectra, SEM, resistivity measurements, x-ray photoelectron spectroscopy and photoluminescence studies. A doping level of 1 at% indium was found to give lowest resistive films and enhanced optical transmission. But increasing the doping percentage resulted in lower optical transmission. XPS investigations revealed the presence of elemental chlorine in the In-doped film. Undoped ZnO thin films gave a strong blue-green emission. Doping with indium apparently resulted in a competitive phenomenon that overshadows the blue-green emission and gave rise to three emissions at 408, 590 and 688 nm.

Generation of terahertz radiation by photomixing with dual- and multiple-mode lasers

Abstract: Photomixing with dual-mode and multi-mode lasers in the sub-terahertz frequency region is presented with a description on the principle and efficiency of photomixing on low-temperature-grown-GaAs photoconductive antennae for generation of continuous-wave terahertz (THz) radiation. The difference frequency stabilization by the common-mode-rejection effect in the dual-mode lasers is discussed with several reported experimental results. It is also shown that generation and detection of broadband sub-THz radiation is possible by photomixing with multi-mode semiconductor lasers on the emitter and detector photoconductive antennae (multi-mode-laser-diode-based terahertz time-domain spectroscopy, MLD-TDS). The MLD-TDS system can be a low-cost and broadband spectrometer in the sub-THz frequency region, which is useful for measurement of complex refractive indices and carrier densities of semiconductor wafers.

Shallow donors and acceptors in ZnO

Abstract: In order to realize controlled p-type doping in ZnO the role of extrinsic and intrinsic donors has to be clarified. The extrinsic n-type dopants Al, Ga and In are commonly found in bulk ZnO crystals, but hydrogen also appears in relevant concentrations eventually controlling the residual n-type carrier concentrations in nominally undoped ZnO. The optical properties of excitonic recombinations in bulk, n-type ZnO are investigated by photoluminescence (PL). At liquid helium temperature the neutral donor–bound excitons dominate in the PL spectrum. Two electron satellite (TES) transitions of the donor–bound excitons allow us to determine the donor binding energies ranging from 46 to 73 meV. In the as-grown crystals a shallow donor with an activation energy of 30 meV controls the conductivity. Annealing annihilates this shallow donor which has a bound exciton recombination at 3.3628 eV. Correlated by magnetic resonance experiments we attribute this particular donor to hydrogen. These results are in line with the temperature-dependent Hall-effect measurements. The Al, Ga and In donor–bound exciton recombinations are identified based on doping and diffusion experiments, and using secondary ion mass spectroscopy. We report on the optical properties of the shallow nitrogen acceptor in ZnO incorporated by diffusion, by ion implantation and by in situ doping in epitaxial films.

Dielectric and infrared properties of TiO2 films containing anatase and rutile

Abstract: Electrical and optical properties of low-temperature, plasma enhanced chemical vapour deposited films of TiO2 have been studied; the source gases were TiCl4 and O2. The amorphous, as-deposited films had a dielectric constant ~33 consistent with their measured density of 3.2 ± 0.2 g cm−3. Films deposited using a −41 V substrate bias contained the anatase phase and some rutile as evidenced from infrared spectroscopy and x-ray scattering. Annealing of these films at 600 °C resulted in a significant increase in the rutile content of the film.

Chemical vapour etching of Si, SiGe and Ge with HCl; applications to the formation of thin relaxed SiGe buffers and to the revelation of threading dislocations

Abstract: We have studied the etching of silicon, SiGe and germanium layers with gaseous HCl in reduced pressure-chemical vapour deposition (RP-CVD). We have observed the occurrence of two etch regimes depending on the etching temperature. The first regime takes place at high temperatures and is characterized by low activation energies (~7 kcal mol−1), this whatever the germanium content of the etched layer. The other regime occurs at low temperatures and has associated high activation energies (which strongly depend upon the germanium concentration of the etched layer: 86 kcal mol−1 for pure Si versus 28 kcal mol−1 for pure Ge). Modifying the HCl partial pressure has different effects depending on the regime. In the high temperature regime, increasing the HCl partial pressure will almost quadratically increase the etch rate (ER ∝ PHCl1.76), this both for Si and Si0.67Ge0.33. Meanwhile, the dependence is sub-linear in the low temperature regime (Si ER ∝ PHCl0.53 and Si0.67Ge0.33 ER ∝ PHCl0.82). The temperature where the regime shifts from one to the other decreases when the Ge concentration increases. To illustrate the added value of the chemical vapour etching, we have demonstrated two possible applications. The first one is the realization of SiGe thin strain relaxed buffers (TSRBs) in the active areas of shallow trench isolation (STI) patterned wafers after etching away the silicon with HCl. We have observed the occurrence of some etching loading effects when moving from a blanket to a patterned wafer. The SiGe TSRBs exhibit some good structural properties (rms roughness of 0.12 nm, no defects observed in cross-sectional transmission electron microscopy). However, they are not fully relaxed and facets are present at the STI/epitaxial stack boundary, signifying they are still not mature enough to be integrated in a metal oxide semiconductor technology. Another possible application is to decorate through some in situ HCl etching the dislocations threading through SiGe relaxed thick layers, with some significant advantages over commonly used wet etching solutions such as the Secco and the Schimmel ones.

Pressurized melt growth of ZnO boules

Abstract: Single crystal zinc oxide is a wide band gap semiconductor with great potential for a variety of commercial applications including substrates, UV photodetectors, acoustic wave devices, light emitting diodes, laser diodes, and high frequency electronic devices. ZnO is unique in that it has a very high exciton binding energy (60 meV) enabling stability at higher device operating temperatures, and it is highly resistant to radiation damage compared even to GaN. Bulk growth of ZnO single crystals is being conducted using the following primary methods: hydrothermal solution growth, seeded sublimation growth, and pressurized melt growth. Cermet, Inc. has employed the pressurized melt growth approach with much success. ZnO dissociates upon heating into a defective ZnO1−x structure, which is addressed by providing an overpressure of oxygen in the growth environment. Single crystals nucleate and grow from the stoichiometric ZnO melt, which is contained in a thin layer of cooled, polycrystalline ZnO, eliminating crucible-introduced impurities. From these large ingots, high quality (~104 defects cm−2, linewidths as low as 49 arcsec), high purity ZnO crystals have been crystallized, oriented, and shaped into round or square boules and eventually processed into epitaxial-ready substrates. The pressurized melt growth approach is highly scalable and can accommodate high growth rates (up to 1 cm h−1), which are two criteria that are appealing to industrial productioin of high quality substrates.

Terahertz lasers based on germanium and silicon

Abstract: Recent experimental and theoretical results of impurity doped germanium and silicon terahertz lasers are reviewed. Three different laser mechanisms exist in p-type germanium. Depending on the operating conditions and the properties of the crystal, laser transitions can occur between light- and heavy-hole subbands, between particular light-hole Landau levels or between impurity states. Electric and magnetic fields are required for laser operation. In n-type silicon lasing originates solely from impurity transitions of group-V donors, which are optically excited. The properties of these lasers depend upon the chemical nature of the impurity centre and the properties of the host material. The principles of operation are discussed in terms of their basic physical concepts. The state-of-the-art performance of these lasers is summarized.

Below bandgap optical absorption in tellurium-doped GaSb

Abstract: Enhancement in below bandgap room temperature infrared transmission has been observed in tellurium (Te)-doped GaSb bulk crystals. The effect of Te concentration on the transmission characteristics of GaSb has been experimentally and theoretically analysed. Undoped GaSb is known to exhibit p-type conductivity with residual hole concentration of the order of (1–2) × 1017 cm−3 at room temperature due to the formation of native defects. For such samples, inter-valence band absorption has been found to be the dominant absorption mechanism. The residual holes could be compensated by n-type dopants such as Te. With increasing Te concentration, free carrier absorption due to electrons and inter-valley transitions in the conduction subband become significant. The dependences of various absorption mechanisms as a function of wavelength have been discussed in this paper.

Conventional n-type doping in diamond: state of the art and recent progress

Abstract: Recent progress in chemical vapour deposition (CVD) diamond technology has enabled the preparation of high-quality n-type CVD diamond layers using phosphorus as a dopant CVD diamond can therefore be considered as a new interesting conventional wide-gap semiconducting material having both n- and p-type dopants, which makes it attractive for numerous applications in high-temperature, high-voltage and high-frequency devices The concentration of phosphorus in n-type CVD diamond can be controlled in the concentration range of 1 × 1016–5 × 1019 cm−3 with a carrier mobility exceeding 600 cm2 V−1 s−1 In this review, the most relevant questions concerning the preparation of P-doped diamond are addressed and discussed in terms of future progress and novel electronic devices We not only discuss the preparation of single crystal epitaxial diamond but also address the growth of large-area n-type polycrystalline CVD diamond, which can be useful for several applications such as for detectors or electron emitters

1024 × 1024 pixel mid-wavelength and long-wavelength infrared QWIP focal plane arrays for imaging applications

Abstract: Mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) 10(24) x 10(24) pixel quantum well infrared photodetector (QWIP) focal planes have been demonstrated with excellent imaging performance. The MWIR QWIP detector array has demonstrated a noise equivalent differential temperature (NEAT) of 17 mK at a 95 K operating temperature with f/2.5 optics at 300 K background and the LWIR detector array has demonstrated a NEAT of 13 mK at a 70 K operating temperature with the same optical and background conditions as the MWIR detector array after the subtraction of system noise. Both MWIR and LWIR focal planes have shown background limited performance (BLIP) at 90 K and 70 K operating temperatures respectively, with similar optical and background conditions. In this paper, we will discuss the performance in terms of quantum efficiency, NE(delta)T, uniformity, operability and modulation transfer functions.

Temperature dependence of electrical parameters of the Au/n-InP Schottky barrier diodes

Abstract: The temperature dependence of current–voltage (I–V) and capacitance–voltage (C–V) characteristics of the Au/n-InP Schottky barrier diodes has been measured in the temperature range of 80–320 K. The forward I–V characteristics are analysed on the basis of standard thermionic emission (TE) theory and the assumption of a Gaussian distribution of the barrier heights (BHs). It has been shown that the ideality factor decreases while the barrier height increases with increasing temperatures, on the basis of TE theory. Furthermore, the homogeneous BH value of approximately 0.524 eV for the device has been obtained from the linear relationship between the temperature-dependent experimentally effective BHs and ideality factors. The modified Richardson plot, according to inhomogeneity of the BHs, has a good linearity over the temperature range. The value of Richardson constant A* has been found to be 5.97 A cm−2 K−2, which is close to the theoretical value of 9.4 A cm−2 K−2 for n-InP. Moreover, the temperature coefficient of the BH is found to be −3.16 × 10−4 eV K−1 for Au/n-InP.

The structural and optical properties of Cu2O films electrodeposited on different substrates

Abstract: Cuprous oxide films were successfully electrodeposited onto three different substrates through the reduction of copper lactate in alkaline solution at pH = 10. The substrates include indium tin oxide film coated glass, n-Si wafer with (001) orientation and Au film evaporated onto Si substrate. The substrate effects on the structural and optical properties of the electrodeposited films are investigated by in situ voltammetry, current versus time transient measurement, ex situ x-ray diffraction, scanning electron microscopy, UV–vis transmittance and reflectance and photoluminescence techniques. The results indicate that the choice of substrate can strongly affect the film morphology, structure and optical properties.

Resonant-phonon-assisted THz quantum-cascade lasers with metal–metal waveguides

Abstract: We report our development of terahertz (THz) quantum-cascade lasers (QCLs) based on two novel features. First, the depopulation of the lower radiative level is achieved through resonant longitudinal optical (LO-)phonon scattering. This depopulation mechanism is robust at high temperatures and high injection levels. In contrast to infrared QCLs that also use LO-phonon scattering for depopulation, in our THz lasers the selectivity of the depopulation scattering is achieved through a combination of resonant tunnelling and LO-phonon scattering, hence the term resonant phonon. This resonant-phonon scheme allows a highly selective depopulation of the lower radiative level with a sub-picosecond lifetime, while maintaining a relatively long upper level lifetime (>5 ps) that is due to upper-to-ground-state scattering. The second feature of our lasers is that mode confinement is achieved by using a novel double-sided metal–metal waveguide, which yields an essentially unity mode confinement factor and therefore a low total cavity loss at THz frequencies. Based on these two unique features, we have achieved some record performance, including, but not limited to, the highest pulsed operating temperature of 137 K, the highest continuous-wave operating temperature of 97 K, and the longest wavelength of 141 µm (corresponding to 2.1 THz) without the assistance of a magnetic field.

Ultrabroadband terahertz pulses: generation and field-resolved detection

Abstract: In this paper, we discuss the latest techniques for the generation and field-resolved detection of tunable femtosecond electromagnetic field transients in a spectral regime covering the complete mid-infrared frequency range. In particular, we review the generation scheme based on phase-matched optical rectification. We also present a novel detection method, exploiting phase-matched electro-optic sampling, which extends the accessible frequency range towards the near-infrared.

High-power 808 nm lasers with a super-large optical cavity

Abstract: We present a detailed design and experimental study of diode laser structures emitting at 808 nm based on the combination of a GaAsP quantum well with well-established AlGaAs waveguide structures By increasing the thickness of the confinement layers of the laser structure, its vertical far field divergence is reduced down to 15° with only a small increase of the threshold current and small loss of efficiency 200 µm aperture 'broad area' devices achieve at a heat sink temperature of 25 °C a continuous wave (CW) output power of more than 15 W with a wall-plug efficiency of 50% with a vertical far field divergence of 18° This output power illustrates the excellent high-power performance by using super-large optical-cavity structures with improved beam characteristics in comparison to the conventional broad waveguide lasers