A 3-D numerical model has been developed to investigate the transient thermal, electrical, and optical output performance of a single-chip light-emitting diode (LED) with an interdigitated mesa geometry under dc operation and a multimicrochip LED under either dc or full-wave operation. These two LED chips are fabricated on the same sapphire wafer. The junction temperature, the light output power, and the electroluminescence intensity of both LEDs are measured under dc to prove the results of the numerical simulations. The numerical simulation results are in good agreement with the experimental ones. The numerical results indicate that the multimicrochip LED under dc operation will demonstrate the best thermal and light output performance. Utilizing the input power considered in the present computation, the light output power for the multimicrochip LED, under either dc or full-wave operation, is raised continuously. On the other hand, the saturation of the light output is observed for the single-chip LED with interdigitated mesa geometry.

Localizing a tiny fault causing abnormal leakage current in a large area P/N junction for a large MOS, diode or BJT structure by nano-probing was demonstrated. The localization was realized through probing the contacts on the junctions and comparing the reversed bias junction current for each contact which maintain the same polarity on the P/N junction. The tiny fault location which is causing the leakage in the large area P/N junction is indicated by the contact with the largest current due to the lowest sheet row resistance path to the fault as measured by nano-probing. Therefore, the success rate to identify the real physical fault by TEM and the ability to take the precise process action to correct the problem is greatly increased by this method. An artificial fault experiment induced by use of FIB as well as real case studies also verifies this method is valid and useful.