Novel evaluation procedure for internal and extraction efficiency of high-power blue LEDs

Internal quantum efficiency (IQE) of a high-brightness blue LED has been evaluated from the external quantum efficiency measured as a function of current at room temperature. Processing the data with a novel evaluation procedure based on the ABC-model, we have determined separately IQE of the LED structure and light extraction efficiency (LEE) of UX:3 chip. Full text Nowadays, understanding of LED efficiency behavior at high currents is quite critical to find ways for further improve­ment of III-nitride LED performance [1]. External quantum ef­ficiency ηe (EQE) provides integral information on the recom­bination and photon emission processes in LEDs. Meanwhile EQE is the product of IQE ηi and LEE ηext at negligible car­rier leakage from the active region. Separate determination of IQE and LEE would be much more helpful, providing correla­tion between these parameters and specific epi-structure and chip design. In this paper, we extend the approach of [2,3] to the whole range of the current/optical power variation, provid­ing an express tool for separate evaluation of IQE and LEE. We studied an InGaN-based LED fabricated by Osram OS. LED structure grown by MOCVD on sapphire substrate was processed as UX:3 chip and mounted into the Golden Dragon package without molding. EQE was measured with Labsphere CDS-600 spectrometer. Plotting EQE versus output power P and finding the power Pm corresponding to EQE maximum ηm enables comparing the measurements with the analytical rela­tionships ηi = Q/(Q+p1/2+p-1/2) ,p = P/Pm , and Q = B/(AC) 1/2 where A, Band C are recombination constants [4]. As a result, maximum IQE value equal to QI(Q+2) can be found from the ratio ηm/ηe plotted as a function of p1/2 +p1-1/2 (see Fig.la) and then LEE calculated as ηext = ηm (Q+2)/Q . Experimental EQE as a function of normalized optical power p is shown in Fig. 1 b along with the analytical approximation based on the ABC­model. The approximation fits perfectly the measurements in the range of the optical power (or operating current) variation by eight orders of magnitude. In conclusion, new express method for separate evaluation of IQE and LEE of III-nitride LEDs is suggested and applied to characterization of a high-brightness blue LED. With this method, we obtained LEE from the free chip surface to the air as 69.8% and IQE as 85.7% at the maximum and 65.2% at the operation current 350 rnA. [I] G. Verzellesi, D. Saguatti, M. Meneghini, F. Bertazzi, M. Goano, G. Meneghesso, and E. Zanoni, "Efficiency droop in InGaN/GaN blue light-emitting diodes: Physical mechanisms and remedies," 1. AppL Phys., vol. 114, no. 7, pp. 071101, Aug., 2013. [2] C. van Opdorp and G. W. 't Hooft, "Method for determining effective non radiative lifetime and leakage losses in double-heterostructure las­ers," 1. AppL Phys., vol. 52, no. 6, pp. 3827-3839, Feb., 1981. [3] M. Meneghini, N. Trivellin, G. Meneghesso, E. Zanoni, U. Zehnder, and B. Hahn, "A combined electro-optical method for the determination of the recombination parameters in InGaN-based light-emitting diodes," 1. AppL Phys., vol. 106, no. II, pp. 114508, Dec., 2009. [4] Qi Dai, Qifeng Shan, ling Wang, S. Chhajed, laehee Cho, E. F. Schubert, M. H. Crawford, D. D. Koleske, Min-Ho Kim, and Yongjo Park, "Carrier recombination mechanisms and efficiency droop in GalnN/GaN light-emitting diodes," App/. Phys. Leu., vol. 97, no. 13, pp. 133507, Sept., 2010. © 2014 IEEE.

Internal versus external R&D:a study of R&D choice with sample selection

This paper extends previous analyses of the choice between internal and external R&D to consider the costs of internal R&D. The Heckman two-stage estimator is used to estimate the determinants of internal R&D unit cost (i.e. cost per product innovation) allowing for sample selection effects. Theory indicates that R&D unit cost will be influenced by scale issues and by the technological opportunities faced by the firm. Transaction costs encountered in research activities are allowed for and, in addition, consideration is given to issues of market structure which influence the choice of R&D mode without affecting the unit cost of internal or external R&D. The model is tested on data from a sample of over 500 UK manufacturing plants which have engaged in product innovation. The key determinants of R&D mode are the scale of plant and R&D input, and market structure conditions. In terms of the R&D cost equation, scale factors are again important and have a non-linear relationship with R&D unit cost. Specificities in physical and human capital also affect unit cost, but have no clear impact on the choice of R&D mode. There is no evidence of technological opportunity affecting either R&D cost or the internal/external decision.

Spatial contrast sensitivity and external noise: applications to optical and neural modulation transfer functions

The thesis will show how to equalise the effect of quantal noise across spatial frequencies by keeping the retinal flux (If-2) constant. In addition, quantal noise is used to study the effect of grating area and spatial frequency on contrast sensitivity resulting in the extension of the new contrast detection model describing the human contrast detection system as a simple image processor. According to the model the human contrast detection system comprises low-pass filtering due to ocular optics, addition of light dependent noise at the event of quantal absorption, high-pass filtering due to the neural visual pathways, addition of internal neural noise, after which detection takes place by a local matched filter, whose sampling efficiency decreases as grating area is increased. Furthermore, this work will demonstrate how to extract both the optical and neural modulation transfer functions of the human eye. The neural transfer function is found to be proportional to spatial frequency up to the local cut-off frequency at eccentricities of 0 - 37 deg across the visual field. The optical transfer function of the human eye is proposed to be more affected by the Stiles-Crawford -effect than generally assumed in the literature. Similarly, this work questions the prevailing ideas about the factors limiting peripheral vision by showing that peripheral optical acts as a low-pass filter in normal viewing conditions, and therefore the effect of peripheral optics is worse than generally assumed.

Adoption of electronic commerce tools in business procurement:enhanced buying center structure and processes

Modern procurement is being shifted from paper-based, people-intensive buying systems toward electronic-based purchase procedures that rely on Internet communications and Web-enhanced buying tools. Develops a typology of e-commerce tools that have come to characterize cutting-edge industrial procurement. E-commerce aspects of purchasing are organized into communication and transaction tools that encompass both internal and external buying activities. Further, a model of the impact of e-commerce on the structure and processes of an organization's buying center is developed. The impact of the changing buying center on procurement outcomes in terms of efficiency and effectiveness is also analyzed. Finally, implications for business-to-business marketers and researchers are discussed.

The individual and society in the GDR under Honecker : orthodoxy, dissidence and internal debate.

The thesis offers a comparative interdisciplinary approach to the examination of the intellectual debates about the relationship between individual and society in the GDR under Honecker. It shows that there was not only a continuum of debate between the academic disciplines, but also from the radical critics of the GDR leadership such as Robert Havemann, Rudolf Bahro and Stefan Heym through the social scientists, literary critics and legal theorists working in the academic institutions to theorists close to the GDR leadership. It also shows that the official line and policy of the ruling party itself on the question of the individual and society was not static over the period, but changed in response to internal and external pressures. Over the period 1971 - 1989 greater emphasis was placed by many intellectuals on the individual, his needs and interests. It was increasingly recognised that conflicts could exist between the individual and society in GDR socialism. Whereas the radical critics argued that these conflicts were due to features of GDR society, such as the hierarchical system of labour functions and bureaucracy, and extrapolated from this a general conflict between the political leadership and population, orthodox critics argued that conflicts existed between a specific individual and society and were largely due to external and historical factors. The internal critics also pointed to the social phenomena which were detrimental to the individual's development in the GDR, but they put forward less radical solutions. With the exception of a few radical young writers, all theorists studied in this thesis gave precedence to social interests over individual interests and so did not advocate a return to `individualistic' positions. The continuity of sometimes quite controversial discussions in the GDR academic journals and the flexibility of the official line and policy suggests that it is inappropriate to refer to GDR society under Honecker simply as totalitarian, although it did have some totalitarian features. What the thesis demonstrates is the existence of `Teiloffentlichkeiten' in which critical discussion is conducted even as the official, orthodox line is given out for public consumption in the high-circulation media.

The contradictions and complementarities of combining ERP systems with enterprise 2.0 supported informal systems

The chapter discusses both the complementary factors and contradictions of adopting ERP based systems with enterprise 2.0. ERP is characterized as achieving efficient business performance by enabling a standardized business process design, but at a cost of flexibility in operations. It is claimed that enterprise 2.0 can support flexible business process management and so incorporate informal and less structured interactions. A traditional view however is that efficiency and flexibility objectives are incompatible as they are different business objectives which are pursued separately in different organizational environments. Thus an ERP system with a primary objective of improving efficiency and an enterprise 2.0 system with a primary aim of improving flexibility may represent a contradiction and lead to a high risk of failure if adopted simultaneously. This chapter will use case study analysis to investigate the use of a combination of ERP and enterprise 2.0 in a single enterprise with the aim of improving both efficiency and flexibility in operations. The chapter provides an in-depth analysis of the combination of ERP with enterprise 2.0 based on social-technical information systems management theory. The chapter also provides a summary of the benefits of the combination of ERP systems and enterprise 2.0 and how they could contribute to the development of a new generation of business management that combines both formal and informal mechanisms. For example, the multiple-sites or informal communities of an enterprise could collaborate efficiently with a common platform with a certain level of standardization but also have the flexibility in order to provide an agile reaction to internal and external events.

Internal market orientation and market/oriented behaviours

Purpose – The purpose of this empirical paper is to investigate internal marketing from a behavioural perspective. The impact of internal marketing behaviours, operationalised as an internal market orientation (IMO), on employees' marketing and other in/role behaviours (IRB) were examined. Design/methodology/approach – Survey data measuring IMO, market orientation and a range of constructs relevant to the nomological network in which they are embedded were collected from the UK retail managers. These were tested to establish their psychometric properties and the conceptual model was analysed using structural equations modelling, employing a partial least squares methodology. Findings – IMO has positive consequences for employees' market/oriented and other IRB. These, in turn, influence marketing success. Research limitations/implications – The paper provides empirical support for the long/held assumption that internal and external marketing are related and that organisations should balance their external focus with some attention to employees. Future research could measure the attitudes and behaviours of managers, employees and customers directly and explore the relationships between them. Practical implications – Firm must ensure that they do not put the needs of their employees second to those of managers and shareholders; managers must develop their listening skills and organisations must become more responsive to the needs of their employees. Originality/value – The paper contributes to the scarce body of empirical support for the role of internal marketing in services organisations. For researchers, this paper legitimises the study of internal marketing as a route to external market success; for managers, the study provides quantifiable evidence that focusing on employees' wants and needs impacts their behaviours towards the market. © 2010, Emerald Group Publishing Limited

Acquirer and owner perceptions of technology integration:the South African case

Developing countries are subject to the same global pressures as their developed counterparts but have additional domestic challenges that may place them at a significant, and perhaps insurmountable, disadvantage. However, technology still offers them the opportunity to participate in the international economy. Difficult conditions in their countries do not absolve managers from formulating and implementing technology policies that can make their firms globally competitive. At a macro-economic level, a number of broad developmental issues impact on the use of technology in developing countries. The subject of this paper is to examine the challenge for South African firms in their efforts to master technology, despite internal and external difficulties. Owners of technology need to consider the local context when supplying their technology to developing markets. The paper aims to investigate the views of technology recipients by examining the perceptions of South African managers regarding technology integration in a manufacturing environment. A number of technology suppliers were also interviewed in order to obtain their opinions on the issues raised by the technology acquirers. The importance of different factors in integrating technology is studied in relation to managers ’ abilities to control these variables. An importance-control grid framework is used to identify critical parameters and to assess how they can be managed in a complex environment.

The East Asian crisis and financing corporate investment:is there a cause for concern?

In view of limited empirical evidence concerning the microeconomic aspects of corporate financial problems in the East Asian countries in the 1990s, this paper analyses the financing pattern of corporate investment in Indonesia, Korea, Malaysia, and Thailand. The analysis is based on an unbalanced panel of listed firms during the period 1989–1997. By using firm size, retention practices, and leverage as three different indicators of financial constraint on firm investment, we have examined the role of various internal and external financing variables on corporate investment in the sample countries. Results indicate that a large number of sample firms depend on free cash flow, especially in Indonesia; there was also a steady increase in debt-equity ratio in all countries. There were signs of agency costs in the use of cash flow in Korea and Malaysia and also in the use of debt financing in Malaysia and Thailand. There was also sign of over-investment among the Thai firms during 1994–1997 though it appears very little if at all was done to redress it in time.

Foreign manufacturing, regional agglomeration and technical efficiency in UK industries: a stochastic production frontier approach

The paper examines howfar foreign manufacturing investment in UK industries, together with the spatial agglomeration of those industries, affect technical efficiency. The paper links research on the estimation of technical efficiency,with those literatures demonstrating the economies associated with foreign direct investment and spatial agglomeration. The methodology involves estimation of a stochastic production frontier with random components associated with industry technical inefficiency, and a standard error. The paper also explores whether the degree of foreign involvement has a greater impact on technical efficiency where the domestic industry sector is characterized by comparatively high productivity and spatial agglomeration. The policy implications of the analysis are discussed.

Trade liberalization and the efficiency of firms in Indian manufacturing

Has the efficiency of firms in India improved since its liberalization in 1991? The authors attempt to answer this question by analyzing the determinants of firm-level efficiency in six manufacturing sectors in India while focusing on the effects of liberalization and domestic competition. They find that there was an increase in overall efficiency in the post-reform period in India in five out of six sectors. While imports do not seem to improve efficiency, liberalization did increase efficiency in four of the sectors.

Do external funds yield lower returns? Recent evidence from East Asian economies

One of the central explanations of the recent Asian Crisis has been the problem of moral hazard as the source of over-investment and excessive external borrowing. There is however rather limited firm-level empirical evidence to characterise inefficient use of internal and external finances. Using a large firm-level panel data-set from four badly affected Asian countries, this paper compares the rates of return to various internal and external funds among firms with low and high debt financing (relative to equity) among financially constrained and other firms. Selectivity-corrected estimates obtained from random effects panel data model do suggest evidence of significantly lower rates of return to long-term debt, even among firms relying more on debt relative to equity in our sample. There is also evidence that average effective interest rates often significantly exceeded the average returns to long-term debt in the sample countries in the pre-crisis period. © 2006 Elsevier Inc. All rights reserved.

ICT and technical efficiency of the manufacturing industries in Iran

This paper extends the existing evidence on the relationship between Information and Communication Technology (ICT) and productivity using data from the entire Iranian manufacturing sector (22 industries) over the period 1993?1999. Estimates of efficiency using panel data confirm the positive and significant impact of ICT investments on productivity. Our finding is consistent with the most recent literatures in the context of developed and a few middle-income developing countries. Human capital and increasing ICT capital are probably two determining factors in gaining the positive payoffs from ICT investments in Iran.

FDI, linkages and the efficiency of state-owned enterprises in China

As China seeks to consolidate its position as an emerging global economic power, reforming the largely inefficient state-owned enterprises (SOEs) presents a major challenge. Using a comprehensive micro data set, we investigate whether SOEs in China have benefited from the managerial, technical and organisational skills possessed by multinational firms operating in the economy, and conclude that the evidence in favour of positive spillovers is not overwhelming. Limited regional linkages and low level of absorptive capacity are found to be the main reasons for this disappointing performance. Policy makers involved in the reform of SOEs should ensure that managers have the right incentives to make long-term investment in absorptive capacity development.