The 1998 EMC: Technical Program Highlights
June 24-26, 1998 · 40TH ELECTRONIC MATERIALS CONFERENCE · Charlottesville, Virginia
Sponsored by the Electronic Materials Committee of The Minerals, Metals & Materials Society (TMS), the 40th Electronic Materials Conference (EMC) will be held June 24-26, 1998, at the University of Virginia, Charlottesville, Virginia.
The EMC is celebrating its 40th year as the leading forum for topics in the areas of preparation and characterization of electronic materials. Participants from industry and universities will meet in Charlottesville to learn about new developments and exchange ideas on emerging technologies. The EMC is held in conjunction with the EMC and 56th Device Research Conference (DRC), the latter taking place on June 22-24 in the same location.
This year's EMC plenary speaker is Laurence Eaves of the University of Nottingham, who will speak about "Superlattices and Resonant Tunnelling: A Quarter-Century Overview." Other highlights of the EMC program are listed below.
III-V Nitrides
Particular attention will be paid to the structural and electronic properties of InGaN. An invited talk by Linda Romano (Xerox PARC) will show that the critical layer thickness for InGaN on GaN can be significantly greater than previously anticipated. The bowing of the InGaN band gap also turns out to be unexpectedly large. Phase separation and homogeneity of InGaN alloys will also be addressed in a number of presentations.
Several groups, including Nichia and Cree Research, will be presenting their latest laser results. Lateral epitaxial overgrowth has recently proven to be an efficient technique for reducing extended defect densities in the nitrides. Several speakers will discuss the effects of growth conditions on materials quality; improvements in device performance will also be addressed.
Other topics will include scanning-tunneling microscopy of GaN surfaces, computational studies of dislocations, selective laser processing for lift-off of GaN thin films from sapphire substrates, As and P incorporation in GaN by MBE, Mg diffusion, and fabrication of GaN-based UV and violet LEDs on Si.
Silicon Carbide
Featured this year is recent work demonstrating vast improvements in the area of ion implantation. In addition, state-of-the-art characterization of oxide and MOS interfaces will be presented. In the area of growth and characterization, striking results will be shown on the topic of growth misorientation effects in 4H-SiC growth, defect analysis of epitaxial layers of up to 0.9 mm thickness, and ion irradiation for device isolation of 4H-SiC.
Contacts to Wide-Band-Gap Materials
Development of high-quality, stable contacts is essential for the continued improvement of wide-band-gap devices. The strong influence of interfacial oxides and/or oxynitrides on the electrical properties of Schottky-barrier contacts to n-GaN will be revealed; more ideal characteristics can be obtained when this interfacial layer is minimized. The annealing ambient has also been identifed as an important variable in the processing of ohmic contacts to p-GaN; annealing in oxygen may increase the acceptor concentration by reactivating Mg acceptors passivated by hydrogen. Lower resistances have been found in ohmic contacts to p-GaN prepared by electrodeposition of Pt, which presumably results in a more intimate contact.
Ultrahigh-vacuum cathodoluminescence studies of buried metal-GaN interfaces highlight the role of deep levels in the contact formation. Chemical preparation, reactive ion etching, and focused-ion-beam modification of the semiconductor surface prior to metallization will be shown to have a strong influence on the electrical characteristics of contacts to wide band gap semiconductors.
Nanoscale Fabrication and Characterization
A number of innovative techniques for fabricating nanostructures will be described. Several approaches utilize natural templates at the nanoscale, such as self-assembled monolayers (SAMs) and "natural" lithographic techniques. Critical processing issues, such as ohmic contacts and process damage to nanostructures, will be addressed, and the electronic quality of fabricated nanodevices will be discussed.
Applications of scanning-probe microscopy to nanometer-scale characterization of semiconductor materials and device structures will be discussed. This work reflects a growing need for nanoscale metrology in microelectronics and optoelectronics. A novel characterization technique based on focused-ion-beam analysis will also be presented. It offers the potential for performing three-dimensiional structural and chemical profiling with spatial resoution of order 10 nm. The application of this technique to characterization of reflowed Al via structures will be discussed.
Growth and Characterization of Quantum Structures
New developments in templated and ordered growth include the integration of InAs quantum dots on Si substrates, and the use of patterned substrates to control the lateral position of self-assembled quantum dots. These advances are important for future generations of quantum functional devices.
Size nonuniformity in ensembles of quantum dots leads to inhomogeneously broadened optical properties. Recent breakthroughs in micro-nano optical techniques allow the properties of single quantum structures to be probed. This ability allows the exciton-photon and exciton-phonon interactions to be studied with unprecedented clarity.
Other highlights of the sessions on nanostructures include: observation of up to 10 excitons in CdSe, InP, and InAs colloidal dots; single-dot spectroscopy; observation of multi-excitonic transitions in self-assembled InAs/GaAs; observation of a full sequence of Coulomb-Blockade transitions in InAs/GaAs; and the extension of pseudopotential theory to million-atom dots.
Materials Integration: Wafer Bonding and Compliant Substrates
Materials integration provides an alternative means of incorporating a variety of device functions within a single structure. The integration of two different semiconductors through wafer bonding for optical applications will be demonstrated. Novel techniques for the integration of widely disparate materials are pursued, using lithium niobate thin films on semiconductor surfaces.
Non-Destructive Testing and In-Situ Monitoring
These characterization techniques are essential for device performance predictions and process control. Applications of optical and electronic measurements will focus on epitaxial materials and device studies. In-situ monitoring of MBE as well as MOCVD will be discussed.
Growth and Characterization of SiGe and SiGeC Heterostructures
New results will be presented on formation of islands and quantum dots, including selective epitaxial growth. The influence of defects and impurities on diffusion in SiGe, and new approaches to control of dislocations will be discussed.
Compound Semiconductor Oxides
Advances in the modeling of the wet oxidation of high-Al-content materials, comparison between conventional and low-temperature-grown AlGaAs/GaAs, and the use of phosphide layers to minimize the problems associated with liberated As will be presented. Wet-oxidation device applications include gallium-arsenide-on-insulator (GOI) FETs and optical applications such as AR coatings and as a matrix for light-emitting Er atoms. MOS devices employing MBE-grown Ga2O3(Gd2O3), and the properties of thermally grown oxide on GaN will also be reported.
Processing
With silicon IC technology continously pushing the limits of device scaling, the defect density and reliability of ultrathin oxide films becomes critical. A new HF vapor treatment will be reported that has resulted in growth of high-quality 11-angstrom-thick oxide layers. The effect of post-oxidation annealing on interface defect densities, resulting in higher breakdown reliability, will also be discussed.
Indium-based oxides have long been recognized as a useful transparent contact material in photonic devices. A reversible process will be reported, whereby the conductive state of the film is switched via photoreduction and via an oxidation process. This approach could prove to have a significant impact on both display and memory technologies.
Epitaxy for Devices
Materials and band-gap engineering efforts result in improved performance of transistors as well as optical and tunneling devices. The use of InAlGaP and GaPSb to replace AlGaAs and InAlAs in HBTs and HEMTs, respectively, will be described, along with recent advances in the study of InAs/AlSb as an alternate material system for HEMTs. The properties of relaxed InAlAs/InGaAs layers on GaAs and a composite InP-InGaAs channel on InP for HEMT applications will also be presented. Other papers will discuss modeling and experimental results for selectively-grown optical interconnects, the use of regrowth to fabricate self-aligned surface tunneling transistors, and the demonstration of CdF2/CaF2/Si resonant tunneling diodes using partially ionized beam epitaxy.
Defects and Device Degradation
A variety of defect-related issues relevant to device design, fabrication, and reliability will be discussed. These include misfit dislocation formation in InGaP/GaAs/Ge tandem solar cells, electron traps due to point & extended defects in InGaAsN alloys, and engineering of the ZnSe/GaAs interface to minimize defect formation. In addition, the effect of deep-level defects and surface passivation on InP-based HEMT performance will be described.
Infrared Materials and Devices
Novel infrared device structures including interband and inter-subband quantum cascade lasers and thermal photovoltaic cells have recently been developed. Theory, design, growth, and characterization of infrared structures will all be addressed. The materials investigated include InGaAsSb quaternary layers, InAlSb/InSb heterostructures, as well as InAs/InGaSb, InAsSb/InAsP, and AlGaAs/GaAs superlattices. Fundamental properties and theoretical descriptions of these narrow-bandgap materials such as recombination processes (e.g., Auger) and band structure will be discussed.
Low-Temperature and Composite Semiconductor Materials
Normally it is difficult to form Schottky contacts to n-type InP owing to surface Fermi-level pinning near the conduction-band edge. This problem has recently been overcome through the incorporation of a GaInP Schottky barrier enhancement layer. HFET device results are comparable to InAlAs/InGaAs HEMTs.
Devices that use Schottky barriers are nearly all of the metal/semiconductor type. Reliable Schottky diodes using InAs/GaP mismatched heterostructures have now been produced at Purdue University. Success is attributed to the large lattice mismatch (~11%) which prevents interdiffusion in this system.
The semi-insulating properties of low-temperature (LT) GaAs are well known and have been exploited in ultrafast photodetector circuits. LT-GaInAs, a desirable material for 1.3-1.5 micron detectors, does not exhibit high resistivity. Be has recently been used to reliably compensate the background donor concentration in LT-GaInAs.
Novel and Artificially Structured Thermoelectric Materials
Quantum confinement and novel approaches to crystal structure modification have stimulated a resurgence in interest and innovation in thermoelectric materials for cooling and power generation. This session will highlight the most promising approaches to the ideal of an "electron crystal/phonon glass".
Electroplated bismuth nanowires have been deposited within the pores of ion-irradiated mica. The promise of quantum confinement will also be illustrated by quantum-well superlattices of PbTe and Si/Ge. New thermoelectric compounds, including skutterudites and Zn4Sb3 will also be featured. The structure and properties of epitaxial Bi2Te3 thin films will be compared to those of bulk single crystals. Finally, progress towards devices and new device concepts will be presented.
Special topical session on New Frontiers in Spontaneous Ordering in Semiconductor Alloys
It is now known that growth of any semiconductor alloy from the gas phase leads to spontaneous, superlattice-like atomic ordering, even though one attempts to grow a random alloy. This ordering has been explained theoretically to result from surface reconstruction.
Interestingly, this novel form of semiconductor alloy structure leads to profound changes in the materials properties, including band-gap narrowing, valence-band splitting, altered effective masses and carrier mobilities, and different pressure-induced response. These changes in material properties upon ordering have found important applications.
Ten specially selected speakers will address the observation and consequences of spontaneous ordering in a variety of materials, including III-V compounds, II-VI compounds, and nitrides.
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