A Low-Temperature Bonding Process Using Mixed Cu–Ag Nanoparticles

A low-temperature bonding process to form joints with high strength and ionic migration resistance using mixed Cu–Ag nanoparticles was studied. Although it was difficult to obtain strong joints using Cu nanoparticles, with the addition of Ag nanoparticles to the Cu nanoparticles the bonding strength of the Cu-to-Cu joints increased. The joints formed by the mixed Cu–Ag nanoparticles at 350°C exhibited a high bonding strength of ~50 MPa. Counterelectrodes made of the mixed Cu–Ag nanoparticles had four times higher ionic migration resistance compared with counterelectrodes made only of Ag nanoparticles.     

Low-Temperature,Strong SiO<Subscript>2</Subscript>-SiO<Subscript>2</Subscript> Covalent Wafer Bonding for III–V Compound Semiconductors-to-Silicon Photonic Integrated Circuits

We report a low-temperature process for covalent bonding of thermal SiO₂ to plasma-enhanced chemical vapor deposited (PECVD) SiO₂ for Si-compound semiconductor integration. A record-thin interfacial oxide layer of 60 nm demonstrates sufficient capability for gas byproduct diffusion and absorption, leading to a high surface energy of 2.65 J/m² after a 2-h 300°C anneal. O₂ plasma treatment and surface chemistry optimization in dilute hydrofluoric (HF) solution and NH₄OH vapor efficiently suppress the small-size interfacial void density down to 2 voids/cm², dramatically increasing the wafer-bonded device yield. Bonding-induced strain, as determined by x-ray diffraction measurements, is negligible. The demonstration of a 50 mm InP epitaxial layer transferred to a silicon-on-insulator (SOI) substrate shows the promise of the method for wafer-scale applications.     

III–V wafer markets

The majority of the world's biggest producers of compound semicon-ductor components are Japanese, as are most of the largest suppliers of the wafers from which these devices are made. Both the production and consumption of all commercially significant categories of III–V wafers - GaP, InP and GaAs - are dominated by diversified Japanese companies.     

Direct calculations on the band offsets of large-lattice-mismatched and heterovalent Si and III–V semiconductors

Band offset in semiconductors is a fundamental physical quantity that determines the performance of optoelectronic devices. However, the current method of calculating band offset is difficult to apply directly to the large-lattice-mismatched and heterovalent semiconductors because of the existing electric field and large strain at the interfaces. Here, we proposed a modified method to calculate band offsets for such systems, in which the core energy level shifts caused by heterovalent effects and lattice mismatch are estimated by interface reconstruction and the insertion of unidirectional strain structures as transitions, respectively. Taking the Si and III–V systems as examples, the results have the same accuracy as what is a widely used method for small-lattice-mismatched systems, and are much closer to the experimental values for the large-lattice-mismatched and heterovalent systems. Furthermore, by systematically studying the heterojunctions of Si and III–V semiconductors along different directions, it is found that the band offsets of Si/InAs and Si/InSb systems in [100], [110] and [111] directions belong to the type I, and could be beneficial for silicon-based luminescence performance. Our study offers a more reliable and direct method for calculating band offsets of large-lattice-mismatched and heterovalent semiconductors, and could provide theoretical support for the design of the high-performance silicon-based light sources.     

Heterostructures in III–V optoelectronic devices

Heterojunctions are used in most III–V optoelectronic devices. Through their use a number of additional degrees of freedom are introduced as compared with homojunction devices. Moreover, new effects, not possible with homojunctions, appear and are applied in many new devices. A classification of heterojunctions is made and their advantages are discussed. The application of heterojunctions in laser diodes is described in some detail.     

On a new method of heterojunction formation in III–V nanowires

The process of the formation of axial heterostructures in nanowires is considered on the basis of the vapor–liquid–solid model of growth. A new method of heterostructure formation in (Al, Ga)As nanowires by varying the arsenic flux is proposed.     

Peculiarities of the Properties of III–V Semiconductors in a Multigrain Structure

The systematized results of studies of the properties of InAs, InSb, and GaAs semiconductors in a multigrain structure based on measurement and analysis of the current–voltage and spectral characteristics are presented. It is established that electron emission and injection are determined by the localization effects of states in the bulk and surface region of submicron grains. The phenomena of current limitation and lowfield emission characteristic of quantum dots are revealed and studied. The results can be used in studies and in the development of multigrain structures for gas and optical sensors, detectors, and emitters of infrared and terahertz ranges.     

III–V compounds as single photon emitters

Single-photon emitters (SPEs) are one of the key components in quantum information applications. The ideal SPEs emit a single photon or a photon-pair on demand, with high purity and distinguishability. SPEs can also be integrated in photonic circuits for scalable quantum communication and quantum computer systems. Quantum dots made from III–V compounds such as InGaAs or GaN have been found to be particularly attractive SPE sources due to their well studied optical performance and state of the art industrial flexibility in fabrication and integration. Here, we review the optical and optoelectronic properties and growth methods of general SPEs. Subsequently, a brief summary of the latest advantages in III–V compound SPEs and the research progress achieved in the past few years will be discussed. We finally describe frontier challenges and conclude with the latest SPE fabrication science and technology that can open new possibilities for quantum information applications.     

Centrotherm: III–V LPE Technology Centre

Centrotherm with its HQ in Blaubeuren, Germany, has established a III–V Technology Center in Alsdorf near Aachen. The equipment installation will permit both demonstration runs and training to be offered to the customer.     

Polarized Retroreflection from Nanoporous III–V Semiconductors

Semiconductors - “Retroreflected light with strong linear polarization coinciding with that of the incident beams is detected from strongly absorbing nanoporous III–V semiconductors....     

Bromine ion-beam-assisted etching of III–V semiconductors

Bromineion-beam-assisted etching produces smooth vertical sidewalls in GaAs, GaP, InP, AlSb, and GaSb as well as in the usual alloys formed from these materials. Care must be taken, however, during etching to match the specific material system with an appropriate substrate etch temperature. For example, vertical walls were obtained using substrate temperatures in the range of 150 to 200°C with InP, 80 to 140°C with GaAs and GaP, and below 30°C with AlSb and GaSb. GaN has also been etched with the technique. Our etching experience and the vapor pressure data for bromine with group III and group V elements lead us to believe that all of the various technologically important III-V binaries, ternaries, and quaternaries can be etched. Etch rates of most of the materials can be varied from several nm/min to 0.16 μm/min through the bromine flow rate, Ar⁺ ion beam density and energy, and the substrate temperature. Bromine ion-beam-assisted etching also appears to have an advantage over chlorine ion-beam-assisted etching in many situations, in that substrate temperature ranges can be found for which vertical sidewalls are maintained while etching through layered structures composed of various alloys of the materials. Here we present results obtained from etching a number of III-V binaries, alloys, and heterostructures.     

Reliability of III–V concentrator solar cells

III–V concentrator solar cells are starting to be commercialized. However, no complete studies about their reliability have been carried out. A review about both the accelerated ageing tests and real time tests developed till now is presented. A proposal about the required tests is also done. In this stage, the tests show that III–V concentrator cells are robust devices with MTTFs well over the expected ones (30 years).     

Inhomogeneous dopant distribution in III–V nanowires

We present a theoretical study of the dopant spatial distribution in III–V nanowires grown by molecular beam epitaxy. The evolution of the dopant concentration is obtained by solving the non-stationary diffusion equation. Within the model, it is shown why and how the dopant inhomogeneity appears, as observed experimentally in the case of Be doping of GaAs nanowires and in other material systems.     

Dynamic nuclear self-polarization of III–V semiconductors

III–V semiconductors exhibit dynamic nuclear self-polarization (DYNASP) owing to the contact hyperfine interaction (HFI) between optically excited conduction electrons and lattice nuclei. In the self-polarization process at a low temperature, electron spin state and the nuclear polarization (magnetization) exchange a positive feedback, increasing energy splitting of the conduction electron states, thereby a large nuclear polarization. This phenomenon was theoretically predicted previously for conduction electrons excited linearly and elliptically polarized light. The polarization of the conduction electrons was represented by a parameterα in a formula for nuclear polarization (Eq. (9) in Ref. [1]); however, the effect of external magnetic fields on the nuclear polarization was not considered. Therefore, this study introduces this effect by further extending the previous studies. Herein, α′ represents the combination of the effects of elliptically polarized electrons and an external magnetic field, which is used in the equations presented in previous studies. When α′ = 0, a large nuclear polarization is obtained below critical temperature T_c, but no polarization occurs above T_c. When α′ > 0, the nuclear polarization is enhanced above T_c. Below T_c, the nuclear polarization follows a hysteresis curve when α′ is partially manipulated by adjusting the degree of the polarization of the exciting laser.     

Lithography scaling issues associated with III–V MOSFETs

In this work we investigate fabrication issues associated with scaling down the gate length and source drain contact separation of a III–V MOSFET. We used high resolution electron-beam lithography and lift-off for gate and ohmic contact patterning to fabricate gate-last lithographically-aligned MOSFETs. This work considers the effect of variations in resist thickness on gate lengths and also the fabrication of long narrow gaps using electron-beam lithography. The study showed that the effect of resist thickness variation on metal linewidth is insignificant. A difference of around 2–3 nm was found between PtAu linewidths fabricated using 150 and 280 nm thick resist. A VB6 lithography tool was found to be useful for linewidth measurements. We showed that the choice of resist is critical to gap formation, and that PMMA is not well suited to this task.