Aluminum Nitride thin films were prepared over different substrates using DC sputtering at room temperature. The prepared films were mostly c-axis oriented on Al substrates. Poor crystalline were recorded for both glass and Si substrates. Cu substrates supported the growth of cubic (2 0 0) AlN. Annealing process showed noticeable effect on c-axis AlN prepared over Al substrates. The observed crystallite sizes were between 9 nm and 79 nm. The applied stress during the growth were tensile nature and showed high value for (1 1 0) phase on Al substrates. The structural parameters such as dislocation density, micro strain etc., were dependent not only the orientation of AlN crystals but also the substrates used. Annealing process showed noticeable reduction on residual stress and micro strain and improvement on crystallite growth as well as the dislocation density.

Thin films of elements (Cd,Te,Ag) were layered as a stack (Te/Cd/Te/Ag/Cd) for doping process with different Ag and Cd thickness by SEL method. The XRD results were depicted the presence of Cubic phase CdTe with (111) orientation along with Ag2Te, CdAgTe, AgTe phases. The peaks related to Ag atom at higher concentration evinced the presence of non-reacted Ag atoms on the surface with higher Ag concentration. The observed results showed the growth of CdTe crystals in (111) orientation with high Ag concentration. The AFM results of the annealed stack were clearly indicated the influence of Ag concentration in grain growth as well as surface roughness. Photo-resistivity studies of the annealed stacks also revealed the effect of Ag concentration in reducing the resistance with difference light sources. The observed results suggested that the SEL method could be used for effective doping of transition metals to achieve desired properties.

Proper heat management is necessary for better performance of the LEDs. In the present study, the thermo-optical properties of the LED with different type of PCBs were analyzed. The measurement was done with two different testing conditions to identify the effect of increasing drive current at constant ambient temperature and increasing ambient temperature at constant drive current on the the LEDs with different PCBs. In both the conditions, the thermal behaviors of the LED are affected much due to different type of boards. As the drive current increases, the junction temperature and RthJA of the LED with MCPCB reduces around 3.7K/W and 15.3K/W compare with the LED with FR4. The change in magnitude of chromaticity coordinates of LED with FR4PCB and MCPCB calculated as 0.154 and 0.132 respectively. At a lower ambient temperature, the LEDs with FR4 and MCPCB record the RthJA as 71.2K/W and 50.6K/W respectively. However, these values were lowered around 15% at higher ambient temperatures for both the LEDs. As ambient temperature increases, the shift in chromaticity coordinates for the LEDs with MCPCB and FR4 was obtained as 0.0163 and 0.0165. The influence of the different type of PCB’s performance on LEDs was observed in the increasing drive current condition rather than the increasing ambient temperatures.

Proper heat management is necessary for better optical performance of high power light emitting diodes (LEDs). However, the thermal behavior of the LEDs differs as the chip technology changes. In this study, the InGaAlP and InGaN based amber and green LED were used to investigate the influence of different operating conditions on its thermal and optical performances. The increasing driving current affects the InGaN LED more than the InGaAlP LED. As the driving current increases, the green and amber LEDs loses its wall-plug efficiency (WPE) from 18.1 to 10% and 31.1 to 27.1% respectively. The higher drop in WPE of green LED was contributed by the higher junction temperature which rises more than 11.1°C than the amber LED. The RthJA was reduced around 4 K/W in green LED and only 1.9 K/W in the amber LED. However, the increasing ambient temperature give significant effect to the thermal behavior of the amber LED. As the ambient temperatures increases, the WPE of the amber LED reduces from 29.7 to 20.7% whereas the green LED loses its efficiency by 0.6%. By investigating the thermal and optical behaviors of the different chip LEDs under different operating conditions, the appropriate working condition of the LEDs at the optimum level can be identified.

Heat management in Light Emitting Diodes (LED) is necessary to enhance its optical performance and stability. The usage of external heat sink is one of the efficient ways to reduce the thermal effect on the LED packages at low cost.

Proper heat management in solid state lighting (SSL) is vital to enhance its efficiency and reliability. The ease of heat flow through the LED package was described in terms of the thermal resistance, Rth. In this study white and green LEDs were used to investigate the variation in junction temperature and junction-to-ambient thermal resistance, RthJA. It was reported that the green LED always shows higher junction temperature and thermal resistance compared to the white LED. This is due to current crowding effect at the p-n junction of the green LED. At 700mA, the RthJA of green LED was increased about 3KW compare with white LED. Furthermore, the die attach quality also influences the temperature rise and thermal resistance of the LED packages. Due to poor die attach, the RthJA rises about 7K/W when compared with good die attach sample.

The surrounding air influence on the thermal transient measurement was studied. The measurements were carried out by setting two boundary conditions where one was measured in open air condition and another transient was captured under still air environment. The data obtained were analysed using structure function evaluation. Analysis of the experimental methods reveal that the thermal resistance of the high power LED is much lower in still air condition compared to open air condition. For the same driving current of 600mA, the total thermal resistance for open air was 8.07692K/W whereas as for still air condition the value was much lower, 7.26577K/W.