........ published in NEWSLETTER # 51
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........ published in NEWSLETTER # 51
SEMICONDUCTOR INTERFACES AT THE SUB_NANOMETER SCALE
by Professor H. Salemink, IBM Research Division, Zurich (Switzerland)
The Advanced Research Workshop on the Physical Properties of Semiconductor Interfaces at the Sub_Nanometer Scale was held from 31 August to 2 September, in Riva del Garda. The papers published in the resulting volume (NATO ASI SERIES E243) reflect the topics discussed at the meeting. The purpose of the workshop was to evaluate the influence of atomic scale fluctuations on nanaometer scale electronic properties like local valence band, energy bandgap, optical levels and crystalline ordering. These will be important issues for the ultimate limits that can be achieved in the manufacture of nanaometer_scale (quantum) devices. Expitaxial growth techniques like MBE and MOVPE have been well advanced in the last 10 years: nevertheless, many views on growth and interface formations are based on the downscaled extrapolation of homogeneous assumptions, which were valid on a more macroscopic scale. The outcome of the workshop might impact the ideas on the details of atomistic growth, role of growth terraces, the definition of compound `interfaces' and the models for growth, bandstructure and band_ offset calculations and compound formation. A major goal is to develop a view as to how such atomic scale fluctuations can influence the physical parameters in nanometer sized structures and devices. Usually the average physical properties are calculated and analyzed with the assumption of homogeneity in the compound material and the electronic bandstructure is predicted using the concept of homogeneous, synthetic (interpolated) crystal potentials. The deviations from ideality become directly observable on the atomic scale using new techniques based on scanning tunneling microscopy (STM). The results from different experimental techniques used for interface analysis, like photoluminescence, Rheed, Leed, TEM, Beem and Xray were presented and inter_compared.
Special attention was given to lectures and discussions describing compound growth on an atomic scale which is a key problem in the controlled growth of quantum structures; opportunities for selective growth will be of importance here, as well as the use of strain and quantum confinement in electro_optical and electron_wave devices.
From a practical point of view, it is important to note that all these details finally affect the properties of nanometer scale electronic devices: for this purpose a session on the relation between growth parameters and device performance was included.
Leading scientists from different disciplines, ranging from theory, growth, analysis and device design, contributed with presentations and discussions in their areas; an attempt was made to develop a cohesive view of subnanometer_scale effects on nanaometer scale devices. Indications of limits and directions for future research and cooperation were formulated.
Reference books: B179, B253, B281, B285, E184, E243