We have analyzed the transport of electrons in the base of a heterojunction bipolar transistor operating in the coherent regime. The analysis is based on the Boltzmann transport equation for the one-electron distribution function. The influence of electron scattering on the transistor current gain in the frequency range beyond the usual cut-off frequency is included in the proposed model. It is demonstrated that the scattering of the electrons in the base region strongly affects the current gain of the heterojunction bipolar transistor in the extended frequency range. Conditions on the relationship between the electron transit times in the base and collector regions and electron scattering rate in the base, which are necessary for the implementation of the current gain beyond the usual cut-off frequency, are found.

Research Center "MICROEL" Krasikov Str. 25a Moscow 11 7218, Russia KEY TERMS Heterojunction bipolar transistor, high-frequency performance, ensemble Monte Carlo particle method ABSTRACTThe high-speed characteristics of InP/InGaAs HBTs with two different collector structures have been investigated using an ensemble Monte Carlo particle simulator. It has been demonstrated that vertical scaling of a standard HBT structure does not result in a substantial improvement of overall speed performance due to the increasing collector capacitance chargine time. As essential reduction of the collector transit delay time has been observed for HBT with nonuniform& doped (n--p+-n--n+) collector structure. The collector transit delay time is reduced due to the extension of the velociy overshoot @on in the collector. The parameters of HBT with proposed collector structure (n--p+-n--n+) have been optimized i n order to obtain the ultimate high-frequency performance under the high collector voltage. 0 1996 John Wiley & Sons, Inc.

The development of logistics in the domestic economy is significantly behind this process in developed countries, both in terms of its accessibility for business entities and in terms of implemented competencies. This is largely due to the use of hierarchical forms of organization of logistics activities, which hinder the efficiency of management decisions in the field of logistics, as well as prevent rapid adaptation to dynamically changing business conditions. This situation for construction business entities is compounded by the lack of a well-established mechanism for their work in the construction market, taking into account changes in legislation on shared-equity construction, as well as the need for early reorientation from narrowfunctional construction work to solving additional consumer problems, increasing the use of technological innovations in the construction sector that change the concept of organizing business processes, relations in the coordinates of "construction firm-consumer". In this regard, it becomes necessary to rethink the approach to organizing logistics activities, which should focus on dynamic relationships between construction organizations, customers, banking structures, investors, construction industry enterprises, supply organizations and transport structures. These circumstances increase the interest in the business environment to the problems of construction logistics, the transformation of construction organizations into real logistics systems that can provide not only a significant economic, but also social effect, since the problem has a pronounced social character. This determined the relevance of the study of the problems of organizing logistics activities in construction and its purpose-the development of theoretical views on the logistics of construction in modern conditions, which will determine the scientific and methodological approaches to the process of creating logistics systems of construction organizations. As the main methods of research on the problems of construction logistics, we used both General scientific methods of knowledge, which allow us to objectively and comprehensively study the conceptual provisions of logistics activities in construction, and private methods (system and complex approaches, dialectical method of scientific knowledge, comparativeanalytical, situational analysis). The main results of the research are the clarification of the categorical logistics apparatus through the formation of methodological approaches to improving the construction management mechanism that is adequate to changing business conditions. The results can be used for research in the field of logistics management at the level of a construction company and the economy of the region.

An ensemble Monte Carlo particle simulation has been used to investigate electron transport in the base region of a heterojunction bipolar transistor operating in the coherent regime. An analytical model of the coherent transistor which includes elastic and quasi-elastic electron scattering has been developed and compared with results of numerical simulation. It has been found that the developed analytical model is in good agreement with the results of numerical simulation. We propose a new expression for the base transport factor of the heterojunction bipolar transistor operating in the coherent regime, which takes into account the influence of thermal dispersion of injected electrons and electron scattering in the base.

Eigh-frequency operation ofnon-planar and planar InP/IaGaAs EBTo with va.rious collector dophg proffles has been investigated usiug a Monte Carlo particle simulation. It is shown that vertical ecaling of collector does not provide a substantial improvement in EBT overall speed performa,uce due to the drastic increase of the collector capacitance charging time with reducirg the collector layer thickness. A considerable impmvement of rrRT high-fiequency performance has been obtaired i! EBT with buried eubcollector a.nd non-uniform collector doping proffle.