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Research Papers

A Comparative Study of Thermal Metrology Techniques for Ultraviolet Light Emitting Diodes

[+] Author and Article Information
Shweta Natarajan

e-mail: shwetan@gatech.edu

Yishak Habtemichael

e-mail: yhabtemich3@gatech.edu

Samuel Graham

Professor
Mem. ASME
e-mail: sgraham@gatech.edu
Woodruff School of Mechanical Engineering,
Georgia Institute of Technology,
Atlanta, GA 30318

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received August 31, 2012; final manuscript received February 5, 2013; published online July 26, 2013. Assoc. Editor: Pamela M. Norris.

J. Heat Transfer 135(9), 091201 (Jul 26, 2013) (8 pages) Paper No: HT-12-1474; doi: 10.1115/1.4024359 History: Received August 31, 2012; Revised February 05, 2013

Methods used to measure the temperature of AlxGa1−xN based ultraviolet light emitting diodes (UV LEDs) are based on optical or electrical phenomena that are sensitive to either local, surface, or average temperatures within the LED. A comparative study of the temperature rise of AlxGa1−xN UV LEDs measured by micro-Raman spectroscopy, infrared (IR) thermography, and the forward voltage method is presented. Experimental temperature measurements are provided for UV LEDs with micropixel and interdigitated contact geometries, as well as for a number of different packaging configurations. It was found that IR spectroscopy was sensitive to optical properties of the device layers, while forward voltage method provided higher temperatures, in general. Raman spectroscopy was used to measure specific layers within the LED, showing that growth substrate temperatures in the flip-chip LEDs agreed more closely to IR measurements while layers closer to the multiple quantum wells (MQWs) agreed more closely with Forward Voltage measurements.

Copyright © 2013 by ASME
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References

Figures

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Fig. 1

Cross-sectional schematic of a micropixel device, showing the multilayered composite device structure

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Fig. 2

Micrograph showing the electrode architecture of the micropixel device, pointing to the p-contact and n-electrode regions

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Fig. 3

Micropixel devices investigated showing (a) the deep UV lamp consisting of a device atop an CTS submount and a TO3 header, (b) device 1 consisting of a device atop an AlNsubmount and a TO66 header, and (c) device 2 consisting of a device atop an CTS submount and a TO66 header

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Fig. 4

Cross-sectional schematic of an interdigitated device, showing the multilayered composite device structure

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Fig. 5

Micrograph showing the interdigitated electrode geometry of the interdigitated device, depicting the p-mesa and the n-electrode

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Fig. 6

The lead-frame package of the interdigitated device

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Fig. 7

The three locations of micro-Raman measurements in the micropixel device shown in relation to the various layers in the device

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Fig. 8

Locations of micro-Raman measurements in the interdigitated shown in relation to the various layers in the device

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Fig. 9

IR thermograph of the interdigitated device, showing the region of highest temperature in the device to be at the edge of p-mesa which was also the location of micro-Raman measurements

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Fig. 10

Raman spectrum between 514 cm−1 and 775 cm−1 of an unpowered micropixel device at 25 °C, showing the Raman peaks of interest

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Fig. 11

Raman spectrum between 566 cm−1 and 672 cm−1 of the unpowered interdigitated device at 40 °C

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Fig. 12

The temperature rises with increasing input powers in the sapphire layer (location III), the AlN layer (location II), and the n-AlxGa1−xN layer (location I) over the MQW, in the DUVL, measured using micro-Raman spectroscopy. The temperature rise presented for location I has been corrected for the effects of inverse-piezoelectric stress.

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Fig. 13

Temperature rises in the AlN layer and the sapphire layer, measured by micro-Raman thermography, and the temperature rise measured by IR thermography, with increasing input powers, for device 1

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Fig. 14

Temperature rises in the AlN and sapphire layers, measured by micro-Raman spectroscopy, and temperature rise measured by IR thermography, with increasing input powers, for device 2

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Fig. 15

Temperature rises for various input powers, for the interdigitated device, in the p-GaN and AlN layers measured through micro-Raman spectroscopy, and from IR spectroscopy and the forward voltage method

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