There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

We present a comprehensive, up-to-date compilation of band parameters for the technologically important III–V zinc blende and wurtzite compound semiconductors: GaAs, GaSb, GaP, GaN, AlAs, AlSb, AlP, AlN, InAs, InSb, InP, and InN, along with their ternary and quaternary alloys. Based on a review of the existing literature, complete and consistent parameter sets are given for all materials. Emphasizing the quantities required for band structure calculations, we tabulate the direct and indirect energy gaps, spin-orbit, and crystal-field splittings, alloy bowing parameters, effective masses for electrons, heavy, light, and split-off holes, Luttinger parameters, interband momentum matrix elements, and deformation potentials, including temperature and alloy-composition dependences where available. Heterostructure band offsets are also given, on an absolute scale that allows any material to be aligned relative to any other.

Band parameters for III–V compound semiconductors and their alloys

Progress in technology, theory and applications of high-frequency mode-locked diode lasers is reviewed. We present a systematic overview of a wealth of experimental and theoretical results and approaches reported recently in the field of physics, technology and applications of monolithic mode-locked laser diodes.

Monolithic and multi-gigahertz mode-locked semiconductor lasers: constructions, experiments, models and applications

ZnO single crystals, epilayers, and nanostructures often exhibit a variety of narrow emission lines in the spectral range between 3.33 and 3.35 eV which are commonly attributed to deeply bound excitons ($Y$ lines). In this work, we present a comprehensive study of the properties of the deeply bound excitons with particular focus on the ${Y}_{0}$ transition at 3.333 eV. The electronic and optical properties of these centers are compared to those of the shallow impurity related exciton binding centers ($I$ lines). In contrast to the shallow donors in ZnO, the deeply bound exciton complexes exhibit a large discrepancy between the thermal activation energy and localization energy of the excitons and cannot be described by an effective mass approach. The different properties between the shallow and deeply bound excitons are also reflected by an exceptionally small coupling of the deep centers to the lattice phonons and a small splitting between their two electron satellite transitions. Based on a multitude of different experimental results including magnetophotoluminescence, magnetoabsorption, excitation spectroscopy (PLE), time resolved photoluminescence (TRPL), and uniaxial pressure measurements, a qualitative defect model is developed which explains all $Y$ lines as radiative recombinations of excitons bound to extended structural defect complexes. These defect complexes introduce additional donor states in ZnO. Furthermore, the spatially localized character of the defect centers is visualized in contrast to the homogeneous distribution of shallow impurity centers by monochromatic cathodoluminescence imaging. A possible relation between the defect bound excitons and the green luminescence band in ZnO is discussed. The optical properties of the defect transitions are compared to similar luminescence lines related to defect and dislocation bound excitons in other II--VI and III--V semiconductors.

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Bound excitons in ZnO: Structural defect complexes versus shallow impurity centers

Wavelength-agile photonic integrated circuits are fabricated using a one-step ion implantation quantum-well intermixing process. In this paper, we discuss, the issues in processing optimized widely tunable multisection lasers using this technique and present the results achieved using this process. This quantum-well intermixing process is general in its application and can be used to monolithically integrate a wide variety of optoelectronic components with widely tunable lasers.

A quantum-well-intermixing process for wavelength-agile photonic integrated circuits

We report a novel technique for quantum well intermixing which is simple, reliable and low cost, and appears universally applicable to a wide range of material systems. The technique involves the deposition of a thin layer of sputtered SiO2 and a subsequent high temperature anneal. The deposition process appears to generate point defects at the sample surface, leading to an enhanced intermixing rate and a commensurate reduction in the required anneal temperature. Using appropriate masking it is possible to completely suppress the intermixing process, enabling large differential band gap shifts (over 100 meV) to be obtained across a single wafer.

A universal damage induced technique for quantum well intermixing

A novel technique for quantum-well intermixing is demonstrated, which has proven a reliable means for obtaining postgrowth shifts in the band edge of a wide range of III-V material systems. The technique relies upon the generation of point defects via plasma induced damage during the deposition of sputtered SiO/sub 2/, and provides a simple and reliable process for the fabrication of both wavelength tuned lasers and monolithically integrated devices. Wavelength tuned broad area oxide stripe lasers are demonstrated in InGaAs-InAlGaAs, InGaAs-InGaAsP, and GaInP-AlGaInP quantum well systems, and it is shown that low absorption losses are obtained after intermixing. Oxide stripe lasers with integrated slab waveguides have also enabled the production of a narrow single lobed far field (3/spl deg/) pattern in both InGaAs-InAlGaAs, and GaInP-AlGaInP devices. Extended cavity ridge waveguide lasers operating at 1.5 /spl mu/m are demonstrated with low loss (/spl alpha/=4.1 cm/sup -1/) waveguides, and it is shown that this loss is limited only by free carrier absorption in waveguide cladding layers. In addition, the operation of intermixed multimode interference couplers is demonstrated, where four GaAs-AlGaAs laser amplifiers are monolithically integrated to produce high output powers of 180 mW in a single fundamental mode. The results illustrate that the technique can routinely be used to fabricate low-loss optical interconnects and offers a very promising route toward photonic integration.

Monolithic integration via a universal damage enhanced quantum-well intermixing technique

The compositional dependence of the electronic band structure of (AlxGa1−x)0.52In0.48P lattice matched to GaAs is reported. Epitaxial layers, grown by solid‐source molecular‐beam epitaxy, with excellent structural and optical quality are obtained over the whole compositional range. Optical spectroscopic techniques are used to study the electronic band structure as a function of composition. The low‐temperature, direct excitonic band gap is found to be given by Eg(x)=1.979+0.704x eV and the lowest band gap becomes indirect for xc=0.50±0.02. The low‐temperature excitonic direct band gap of Al0.52In0.48P is measured to be 2.680 eV.

Electronic band structure of AlGaInP grown by solid‐source molecular‐beam epitaxy

Precise control over local optical and electrical characteristics across a semiconductor wafer is a fundamental requirement for the fabrication of photonic integrated circuits. Quantum well intermixing is one approach, where the band gap of a quantum well structure is modified by intermixing the well and barrier layers. Here we report recent progress in the development of intermixing techniques for long wavelength applications, discussing two basic techniques. The first is a class of laser disordering techniques which take place in the solid state. The second is a novel intermixing technique involving plasma induced damage. Both techniques enable large band gap shifts to be achieved in standard GaInAsP multiple quantum well laser structures. The potential of both techniques for photonic integration is further demonstrated by the fabrication and characterisation of extended cavity lasers.

Quantum well intermixing in material systems for 1.5 μm (invited)

There is disclosed an improved method of manufacturing an optical device using an impurity induced Quantum Well Intermixing (QWI) process. Reported QWI methods, and particularly Impurity Free Vacancy Diffusion (IFVD) methods, suffer from a number of disadvantages, eg the temperature at which Gallium Arsenide (GaAs) out-diffuses from the semiconductor material to the Silica (SiO2) film. Accordingly, the present invention provides a method of manufacturing an optical device, a device body portion (5a) from which the device is to be made including at least one Quantum Well (QW) (10a), the method including the steps of: causing an impurity material to intermix with the at least one Quantum Well (QW) (10a), wherein the impurity material at least includes Copper (Cu).

Olek P. Kowalski

Papers

A universal damage induced technique for quantum well intermixing

Monolithic integration via a universal damage enhanced quantum-well intermixing technique

Electronic band structure of AlGaInP grown by solid‐source molecular‐beam epitaxy

Quantum well intermixing in material systems for 1.5 μm (invited)

Method of manufacturing optical devices and related improvements