Photometers are widely used for the measurement of the average LED intensity as defined by CIE 127, under the circumstance that LEDs have many kinds of intensity spatial distributions. Significant measurement errors can be resulted due to the following facts: 1) a photometer with a diffuser generally has a spatial response that is stronger in the center of the detector; and 2) LED angular distributions of intensity often have a sidelobe about the central axis rather than a central peak. A special measuring facility for illuminance intensity distribution of LEDs and spatial response distribution of photometers has been designed. An evaluation factor Bc[ has been introduced to describe the spatial response distribution uniformity of photometers. Three kinds of photometers with different spatial response distribution were used to measure the averaged LED intensity individually. Experiment shows that the photometer with a diffuser has a response distribution of a cosine function, and the illuminance intensity distribution of LEDs generally presents a sine, trapezoidal, or cosine function with the 6.5 field of view for CIE Condition B. The results show that the measurement errors could be more than À5.10% when using the photometer with a diffuser to measure the average intensity of LEDs with a narrow beam angle. It is very important that the uniformity of spatial response distribution of the photometer should be considered when calibrating Averaged LED Intensity as it can introduce a significant error.

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The effect of the number of layers and the length of the heat shields on the heating efficiency and temperature distributions in the substrate have been studied by establishing the model of a single-piece 18-inch MOCVD reactor. The results show that the number of layers of the heat shields is directly proportional to the heating efficiency, decreasing the length of the thermal shield can reduce the standard deviation(STD) of the substrate temperature. When the length of the heat shields is 56mm, the coefficient of substrate temperature STD is 21.41 °C and the STD is about 45% lower than the traditional susceptor. An area within substrate radius of 200mm, the coefficient of substrate temperature STD is 2.64 °C and the STD is about 93% lower than the traditional susceptor. The results obtained will provide theoretical basis for developing the heating structure of large-sized MOCVD reactor.

A pallet structure with an annular slot is proposed in the perpendicular MOVPE chamber by electromagnetic heating Compared with the conventional pallet, the shape of the slot changes the directions of the thermal conduction in the pallet, which makes the temperature distribution of the substrate more uniform. The optimized pallet structure which makes the most uniform temperature profile of the substrate is also given. In addition, the intervals of the applied parameters such as the current frequency, current strength and coil turns which keep the stable change of the substrate temperature are also obtained, by analyzing the change of the substrate temperature with the parameters. When one of the parameters is changed in the interval, the temperature magnitude can be adjusted while ensuring a certain uniformity of the temperature. This is beneficial to control the growth of the thin film.

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