Advances in the technology of electronic and optoelectronic devices are often a result of the development of new material systems with properties that are superior to those of existing materials. This happened when silicon replaced germanium in the early years of the semiconductor industry. Another time this happened was when gallium arsenide emerged as a semiconductor of choice for building extremely fast devices. A similar development may be in the offing for optoelectronics this time with the advent of zinc oxide (ZnO). This is a promising material that might one day substantially replace gallium nitride (GaN) as the material of choice for making short-wavelength light emitters and detectors. ZnO—a II–VI oxide semiconductor—possesses properties that are broadly similar to that of GaN, which is now almost universally used for making blue light-emitting diodes (LEDs) and violet lasers, as well as a number of other devices. A number of years ago, GaN emerged as the leading material from which short-wavelength optoelectronic devices are fabricated. Its dominance has remained unchallenged so far and has only grown with further advances in the technology of III-nitrides. ZnO now appears to have the potential to challenge the pre-eminence of III-nitrides, but whether it lives up to its promise in the coming years will depend on whether the considerable challenges that remain before this material becomes industrially useful could be overcome in an acceptable manner. Mere laboratory advances will not be sufficient—robust and reliable processes will have to be developed that could be used to routinely fabricate efficient, stable, and long-lived devices on a large scale. Nevertheless, working devices have been built from ZnO and related materials that show the potential inherent in this material system. LEDs made from ZnO have received the most attention to date and the aim of this focused review is to highlight the various approaches that have been taken in recent years to fabricate both heterojunction and homojunction ZnO LEDs. The high binding energy of excitons in ZnO, relative to thermal energy at room temperature, makes ZnO LEDs and diode lasers potentially brighter than comparable devices made from other semiconductors. This can have dramatic consequences for near- and mid-ultraviolet (UV) emitters where GaN has not performed so well in terms of cost and device efficiency. If potential problems with ZnO family semiconductors, as outlined later in this paper, could be overcome then high-brightness solid-state light sources will become possible for such budding applications as water purification, resin cross-linking, microprinting, high-density data storage, non-line-of-sight optical communication, and indoor plant growth, to name a few. However, in order to enable these advances and to open new markets, considerable work still needs to be done to perfect the art of making high-quality ZnO-based pn-junctions.

Energy efficiency and lighting quality considerations are driving research into laser-pumped white light sources. Laser diodes as pump sources for downconversion phosphors promise freedom from “droop” that adversely affects the efficiency of light-emitting diodes (LEDs). High-intensity laser diode-pumped light sources for applications such as search lights and automobile headlights have been demonstrated recently. Our paper describes the design and construction of a domestic/office-type solid-state luminaire driven by light from an integrated violet laser-diode module. A trichromatic phosphor made from a blend of separate europium-containing rare-earth phosphors was used as the downconversion medium. Mechanical and optical design of the reflector and the phosphor plate are described. Characteristics of both the pump light and the downconverted light are also described. Our studies also looked at the variation of chromaticity coordinates with variation in pump power and the effect of laser speckle on the lamp’s light output. Finally, there is a brief discussion of energy conversion efficiency and longevity considerations, comparing pumping with LEDs versus pumping with laser diodes.

Over the past two decades, solid-state light sources that rely on a semiconductor light-emitting device to generate light for illumination purposes have largely taken over from incandescent and discharge lamps.^{1 – 4} These new light sources have the benefits of small size, high efficiency operation, long operating lifetimes, and environmental sustainability. Given that space lighting accounts for a substantial portion of humankind’s total energy usage, this shift has been a defining development of our times. In the United States alone, around 219 billion kWh of energy is used annually for artificial lighting. Had highly energy efficient solid-state lighting not been invented, a much larger amount of energy would have been used for this purpose.

We describe in detail the growth procedures and properties of thermal silicon dioxide grown in a limited and dilute oxygen atmosphere. Thin thermal oxide films have become increasingly important in recent years due to the continuing down-scaling of ultra large scale integration metal oxide silicon field effect transistors. Such films are also of importance for organic transistors where back-gating is needed. The technique described here is novel and allows self-limited formation of high quality thin oxide films on silicon surfaces. This technique is easy to implement in both research laboratory and industrial settings. Growth conditions and their effects on film growth have been described. Properties of the resulting oxide films, relevant for microelectronic device applications, have also been investigated and reported here. Overall, our findings are that thin, high quality, dense silicon dioxide films of thicknesses up to 100 nm can be easily grown in a depleted oxygen environment at temperatures similar to that used for usual silicon dioxide thermal growth in flowing dry oxygen.

We have studied transport in mesoscopic superconductor-semiconductor hybrid structures consisting of two-dimensional arrays of micrometer-sized niobium dots deposited on high-mobility InAs:GaSb quantum wells. The grating arrays were designed to have a dot size and spacing of 3, 1.5, and 1 μm, so as to be smaller than the electron mean free path of ∼5 μm. At low temperatures all the structures show clear evidence of Andreev reflection while the two smaller period samples also exhibit a proximity-induced superconducting phase. We present measurements of the differential resistance at different temperatures and magnetic fields. For fields greater than 0.3 T, different features are observed in the differential resistance which we attribute to nonuniform flux penetration around the superconducting dots. © 1996 The American Physical Society.

Material growth and etching processes that cause the formation or removal of one atomic or molecular layer at a time are becoming commonplace. Starting from the research labs, such atomic layer process technologies have now migrated to the fab floor. This compact review examines the reasons behind the popularity of these techniques through both a tutorial approach and by citing relevant works that show the practical uses of both additive and subtractive atomic layer processes. Succinct introductions to both atomic layer deposition (ALD) and atomic layer etching (ALE) have been provided. Beyond that, this review examines, in particular, seed layer growth and plasma-enhanced ALD (PEALD), as well as various applications of ALE for the removal of semiconductors, metals and dielectrics.