ISSN 1063-7826, Semiconductors, 2010, Vol. 44, No. 3, pp. 373–379. © Pleiades Publishing, Ltd., 2010. Original Russian Text © A.L. Zakgeim, G.L. Kuryshev, M.N. Mizerov, V.G. Polovinkin, I.V. Rozhansky, A.E. Chernyakov, 2010, published in Fizika i Tekhnika Poluprovodnikov, 2010, Vol. 44, No. 3, pp. 390–396. 373 1. INTRODUCTION In recent years, the efficiency of semiconductor light-emitting diodes (LEDs) based on AlInGaN het- erostructures has been rapidly rising, which makes these devices the most promising sources of light to replace conventional incandescent lamps in the near future. One of the critical conditions for application of LEDs for illumination purposes is that the light flux from a single emitter should be raised, which can be done by making the area of emitting chips larger and the current load and admissible working temperatures higher. The standard, for the time being, devices are those with a p–n junction area of ~1 mm 2 , working currents of 350–1000 mA (current density J ≈ 35– 100 A cm –2 ), and dissipated power of several watts. According to prognoses [1], both the dimensions of emitting chips and their specific current loads will increase twofold to threefold by 2010–2012. As an illustration of the recent tendencies in the develop- ment of high-power LEDs can be mentioned devices of the Phlatlight series (Luminus Devices, Inc., United States) with a p–n junction area of 12 mm 2 and a working current of 18 A [2]. A particularly acute issue for LEDS operating at high excitation levels is the problem of removal of the released heat and precision control over the tempera- ture of the active region. It is known that heating pro- foundly affects both the functional characteristics of LEDs and their reliability and service life. It is note- worthy that, for large-area devices with a complex configuration of contacts, it is important to know not only the average temperature of the active region, which can be calculated from the heat resistance, but also the detailed distribution pattern of temperature fields by performing the so-called temperature “map- ping.” The reason for this is that modern light-emit- ting chips based on AlGaInN and AlGaInP nanohet- erostructures are for the most part of mesa planar (flip- chip) design with single-side contacts and a thin active region grown on an insulating substrate. Taken together, these factors result in a substantial lateral, along the p–n junction plane, component of the cur- rent and in the current crowding over the p–n junction area [3–5]. At the same time, the widely used flip-chip mounting technique, in which a chip is attached to a carrier plate with separate solder bumps, leads to inho- mogeneous heat removal because of the formation of soldered (heat-conducting) and “hanging” (thermally insulated) regions. Both these factors may give rise to substantial temperature gradients over the chip area and to locally overheated regions potentially hazard- ous to device operation. Indirect methods for measuring the thermal parameters of LEDs are known and widely used. These methods are based on temperature dependences of the electrical [6] or spectral characteristics of LEDs [7, 8]. However, these techniques yield not too precise and, as a rule, averaged results. In principle, the tem- perature “mapping” can be done by analyzing elec- troluminescence (EL) spectra recorded with scanning PHYSICS OF SEMICONDUCTOR DEVICES A Study of Thermal Processes in High-Power InGaN/GaN Flip-Chip LEDs by IR Thermal Imaging Microscopy A. L. Zakgeim a ^, G. L. Kuryshev b , M. N. Mizerov a , V. G. Polovinkin b , I. V. Rozhansky c , and A. E. Chernyakov a a Scientific Technological Center for Microelectronics and Submicrometer Heterostructures, Ioffe Physicotechnical Institute, Russian Academy of Sciences, St. Petersburg, 194021 Russia ^e-mail: zakgeim@mail.ioffe.ru b Institute of Semiconductor Physics, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia c Ioffe Physicotechnical Institute, Russian Academy of Sciences, St. Petersburg, 194021 Russia Submitted July 30, 2009; accepted for publication, August 20, 2009 Abstract—Results of an experimental study of temperature fields generated in high-power AlGaInN hetero- structure flip-chip light-emitting diodes (LEDs) via their self-heating at high working currents are presented. The method of IR thermal imaging microscopy employed in the study enables a direct measurement of the temperature distribution over the p–n junction area with a high resolution of ~3 μm at an absolute measure- ment error of ~2 K. It is shown that large temperature gradients may arise in high-power LEDs at high exci- tation levels as a result of current crowding. This effect should be taken into account when designing light- emitting chips and estimating the admissible operation modes. The method of IR thermal imaging microscopy can also reveal microscopic defects giving rise to current leakage channels and impairing device reliability. DOI: 10.1134/S1063782610030176