The junction temperature of AlGaN ultraviolet light-emitting diodes emitting at 295nm is measured by using the temperature coefficients of the diode forward voltage and emission peak energy. The high-energy slope of the spectrum is explored to measure the carrier temperature. A linear relation between junction temperature and current is found. Analysis of the experimental methods reveals that the diode-forward voltage is the most accurate (±3°C). A theoretical model for the dependence of the diode forward voltage (Vf) on junction temperature (Tj) is developed that takes into account the temperature dependence of the energy gap. A thermal resistance of 87.6K∕W is obtained with the device mounted with thermal paste on a heat sink.

Dissociative chemisorption of CH 4 on a cesiated Pt (111) A new instrument employing molecular beam techniques and laser induced fluorescence ͑LIF͒ for measuring the reactivity of gas phase radicals at the surface of a depositing film has been designed and characterized. The instrument uses an inductively coupled plasma source to create a molecular beam containing essentially all plasma species. A tunable excimer pumped dye laser is used to excite a single species in this complex molecular beam. LIF signals are imaged onto a gated, intensified charge coupled device ͑ICCD͒ to provide spatial resolution. ICCD images depict the fluorescence from molecules both in the molecular beam and scattering from the surface of a depositing film. Data collected with and without a substrate in the path of the molecular beam provide information about the surface reactivity of the species of interest. Here, we report the first measurements using the third generation imaging of radicals interacting with surfaces apparatus. We have measured the surface reactivity of SiH molecules formed in a 100% SiH 4 plasma during deposition of an amorphous hydrogenated silicon film. On a 300 K Si ͑100͒ substrate, the reactivity of SiH is near unity. The substrate temperature dependence ͑300-673 K͒ of the reactivity is also reported. In addition, reactivity measurements for OH molecules formed in a water plasma are presented. In contrast to the SiH molecule, the reactivity of OH radicals is 0.55Ϯ0.05 on the surface of a Si ͑100͒ substrate.

Ultraviolet light-emitting diodes (LEDs) have been grown by metalorganic vapor phase epitaxy using AlN nucleation layers and thick n-type Al0.48Ga0.52N current spreading layers. The active region is composed of three Al0.36Ga0.64N quantum wells with Al0.48Ga0.52N barriers for emission at 290 nm. Devices were designed as bottom emitters and flip-chip bonded to thermally conductive submounts using an interdigitated contact geometry. The ratio of quantum well emission to 330 nm sub-band gap emission is as high as 125:1 for these LEDs. Output power as high as 1.34 mW at 300 mA under direct current operation has been demonstrated with a forward voltage of 9.4 V. A peak external quantum efficiency of 0.18% has been measured at an operating current of 55 mA.

The OH(X 2 Π) radical in a 20:80 tetraethoxysilane (TEOS)/O 2 plasmas has been characterized during deposition of SiO 2 using the imaging of radicals interacting with surfaces (IRIS) method. The reactivity of OH at the surface of a growing SiO 2 film has been determined as a function of the applied radio-frequency (rf) plasma power (P) and the substrate temperature (T S ). The reactivity (R) of OH during deposition of SiO 2 on a 300 K Si substrate is 0.41 ( 0.04. R decreases as substrate temperature increases but is unaffected by increasing rf power. Translational and rotational temperatures (Θ T and Θ R , respectively) of the OH radical are also determined. For a 20:80 TEOS/O 2 plasma (P ) 85 W), Θ T ) 912 ( 20 K and Θ R ) 450 ( 20 K. Θ T is significantly higher than Θ R and increases with increasing rf power. Using isotopically labeled 18 O 2 as a precursor, the source of the oxygen in OH is identified as the O 2 gas, not oxygen from the ethoxy groups on TEOS. With these data, the role of OH in deposition of SiO 2 from TEOS-based plasmas and the effects of plasma deposition parameters on film formation are discussed.

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