Materials Science Forum Vol. 590

Abstract: A brief history of visible light-emitting diodes (LED's) is given, from the first experimental observations of H.J.Round in 1907 to the mid-1970's when red and green emitters were in extensive production. Early investigations were empirical. This was changed with the invention of the transistor in 1947 by the demonstration of minority carrier injection at a forwardbiased junction, followed by recombination. In 1952 the discovery of the semiconducting behaviour of III-V compounds introduced a new range of materials. Gallium nitride seemed attractive for light emission and was investigated at Philips and RCA laboratories but at the time proved to be too difficult for practical use. Gallium phosphide emerged as the most promising material and groups to investigate it were set up at SERL in England, Philips Central Research Laboratories in Germany and Bell Telephone Laboratories in the USA. Zinc and oxygen doping gave red emission. At Philips, the emphasis was on efficiencies. At SERL the emphasis was on reproducibility for manufacturable devices and when the conditions for zinc and oxygen doping were strictly controlled the world's first practical visible LED's were produced at the end of 1961. At Bell Telephone Laboratories progress was initially slow but with the advent of liquid-phase epitaxial growth production of red emitters on the scale required became possible. The accidental discovery of nitrogen doping of gallium phosphide at Bell led to the production of good green emitters. Until the end of the 1970's, gallium phosphide red and green emitters dominated the LED market. Subsequent developments to the present day are sketched in outline.

Abstract: This chapter serves as an introduction to the chapters on III-nitrides in this book. It gives a brief review of the development of relevant III-nitride materials for light emitters since the late 1960´s, when single crystalline GaN layers grown on sapphire were first demonstrated. The first wave of scientific work died out in the late 1970´s, since low-ohmic p-GaN could not be made at the time. After another 10 years several important breakthroughs were made, using the technology of metal organic vapor phase epitaxy (MOVPE). Smooth thin epilayers could be made, and ways to dope the materials n-type as well as p-type were invented. In the period 1986-1997 high brightness violet and blue double heterostructure (DH) LEDs, narrow quantum well (QW) LEDs, and QW based violet laser diodes with a long operating lifetime of 10000 hours were demonstrated, mainly by Japanese groups. Since then the development efforts have spread worldwide, and a large spectrum of novel applications based on nitride emitters are already in practical use. Perhaps the most important one is the future possibility of using nitride LEDs for general lighting purposes.

Abstract: There is a growing demand for a silicon-based light emitters generating a light with a wavelength in of 1.3-1.6 μm range, which can be integrated into silicon chips and used for in-chip opto-electronic interconnects. Among other possibilities, the D1 luminescence at about 1.55 m, caused by dislocations in Si, can be a suitable candidate for such in-chip light emitters. Here we present a brief review of today knowledge about electronic properties of dislocations in silicon and dislocation-related luminescence in connection with possible application of this luminescence for silicon infrared light-emitting diodes (Si-LEDs).

Abstract: The paper reviews methods of hydrophobic wafer bonding. Hydrophobic surfaces are obtained by removing the oxide layer from the surfaces of crystalline silicon substrates. Bonding such surfaces causes the formation of a dislocation network in the interface. The structure of the dislocation network depends only on the misalignment (twist and tilt components). The different dislocation structures are discussed. Because wafer bonding offers a method to the reproducible formation of such networks, different applications are possible

Abstract: Single crystal Si, Si0.948Ge0.052 and Si0.66Ge0.34 diodes as well as Ge transistor structures with high electroluminescence (EL) intensities in the region of interband transitions at room temperature were fabricated by different techniques and their luminescence properties were studied. By varying the Ge content in the solid solution, one can control the wavelength at the emission maximum in the range of 1.1 - 1.8 μm. The integrated EL intensity varies by a factor of less than two in the temperature ranges of 80 - 500 and 80 - 300 K for Si and SiGe LEDs, respectively. Si LEDs can effectively operate, at least, up to ~200°C. The data analysis shows that recombination involving excitons is the dominant mechanism of near-band-edge radiative recombination in all the light-emitting structures at room temperature. Some of the structures have record values of EL intensity and/or quantum efficiency, so they can be used as effective light emitters in Si optoelectronics. In particular, Si LEDs were designed with a small p-n junction area of 8x10-3 mm2 and a radiation power of 0.3 mW. The record total emission power of 46 mW was achieved in solar cell LEDs with an emitting surface area of 3 сm2. The internal quantum efficiencies of 0.5% and 0.3% were recorded in Si0.948Ge0.052 and Si0.66Ge0.34 LEDs at the wavelengths of 1.15 and 1.3 μm, respectively. Room temperature near-band-edge EL was first observed in Ge structures.

Abstract: Silicon-On-Insulator (SOI) technology exhibits significant performance advantages over conventional bulk silicon technology in both electronics and optoelectronics. In this chapter we present an overview of recent applications on light emission from SOI materials. Particularly, in our work we used SOI technology to fabricate light emitting diodes (LEDs), which emit around 1130 nm wavelength with an external quantum efficiency of 1.4 × 10−4 at room temperature (corresponding to an internal quantum efficiency close to 1 %). This is almost two orders of magnitude higher than reported earlier for SOI LEDs. This large improvement is due to three carrier confinement mechanisms: geometrical effects, quantum-size effects, and electric field effects. Our lateral p+/p/n+ structure is powered through two very thin silicon slabs adjacent to the p+/p and n+/p junction. Such use of thin silicon films aims to reduce the p+ and n+ contact area and to confine the injected carriers in the central lowly doped p-region. With this approach, we realized an efficient compact infrared light source with high potential switching speed for on-chip integration applications.

Abstract: In this article we will give an overview of our work devoted to Si-based light emission which was done in the last years. Si-based light emitters were fabricated by ion implantation of rare earth elements into the oxide layer of a conventional MOS structure. Efficient electroluminescence was obtained for the wavelength range from UV to the visible by using a transparent top electrode made of indium-tin oxide. In the case of Tb-implantation the best devices reach an external quantum efficiency of 16 % which corresponds to a power efficiency in the order of 0.3 %. The properties of the microstructure, the IV characteristics and the electroluminescence spectra were evaluated. The electroluminescence was found to be caused by hot electron impact excitation of rare earth ions, and the electric phenomena of charge transport, luminescence centre excitation, quenching and degradation are explained in detail.

Abstract: Ultraviolet light emitting diodes with emission wavelengths less than 400 nm have been developed using the AlInGaN material system. Rapid progress in material growth, device fabrication and packaging enabled demonstration of deep-UV light-emitting devices with emission from 400 to 210 nm with varying efficiencies. For high aluminum alloy compositions needed for the shorter wavelength devices, these materials border between having material properties like conventional semiconductors and insulators, adding a degree of complexity to developing efficient light emitting devices. This chapter provides a review of III-nitride based UV light emitting devices including technical developments that allow for emission in the ultraviolet spectrum, and an overview of their applications in optoelectronic systems.

Abstract: The fundamental growth issues of AlN and AlGaN on sapphire and SiC using metalorganic vapor phase epitaxy, particularly the growth of AlN and AlGaN on a groove-patterned template are reviewed. In addition, the conductivity control of AlGaN is shown. The conductivity control of p-type AlGaN, particularly the realization of a high hole concentration, is essential for realizing high-efficiency UV and DUV LEDs and LDs.