The effects of p- and n-electrode patterning on the current spreading and driving voltage of a side-view GaN∕sapphire light-emitting diode (LED) chip are investigated via a numerical simulation. The numerical results (current distributions) for the striped pattern p-electrode are well consistent with the optical emission patterns taken from emission images. A desirable uniformity of the current distribution in the active layer can be obtained by the appropriate arrangement of p- and n-electrode patterns. At the same time, a lower voltage drop in the LED chip is also obtained due to a more uniform current distribution in the p-GaN layer and a smaller overall distance for current movement in the n-GaN layer. With an injection current of <mml:math display="inline"><mml:mrow><mml:mn>30</mml:mn><mml:mspace width="0.3em"></mml:mspace><mml:mi>mA</mml:mi></mml:mrow></mml:math>30mA , a decrease in driving voltage of 13% for well-designed electrode patterns can achieve compared to the control devices considered in this study.

The influence of the size of an n-electrode and a current blocking layer (CBL) on the thermal and electrical characteristics of a vertical-injection GaN-based light emitting diode (LED) chip is investigated by numerical simulation. The predicted forward voltages are quite consistent with previous experimental data. The coupled thermal and electrical effects affect the performance of a LED chip. For cases without a CBL, the variation in current density and temperature distributions in the active layer, and the forward voltage and Joule heating percentage of the LED chip increase as the n-electrode width <mml:math display="inline"><mml:mrow><mml:mrow><mml:mo>(</mml:mo><mml:mi>L</mml:mi><mml:mo>)</mml:mo></mml:mrow></mml:mrow></mml:math>(L) decreases. The current crowding and temperature of the hot spot are very significant, although the wall-plug efficiency (WPE) is the highest one obtained for <mml:math display="inline"><mml:mrow><mml:mi>L</mml:mi><mml:mo>=</mml:mo><mml:mn>100</mml:mn><mml:mspace width="0.5em"></mml:mspace><mml:mi>μ</mml:mi><mml:mi mathvariant="normal">m</mml:mi></mml:mrow></mml:math>L=100μm . The better width of the n-electrode in terms of the uniformity of temperature, current density distribution, WPE, and forward voltage may be the case where <mml:math display="inline"><mml:mrow><mml:mi>L</mml:mi><mml:mo>=</mml:mo><mml:mn>200</mml:mn><mml:mspace width="0.5em"></mml:mspace><mml:mi>μ</mml:mi><mml:mi mathvariant="normal">m</mml:mi></mml:mrow></mml:math>L=200μm . The insertion of a CBL into a <mml:math display="inline"><mml:mrow><mml:mn>600</mml:mn><mml:mo>×</mml:mo><mml:mn>600</mml:mn><mml:mspace width="0.5em"></mml:mspace><mml:mi>μ</mml:mi><mml:mi mathvariant="normal">m</mml:mi></mml:mrow></mml:math>600×600μm chip leads to greater uniformity in the distribution of the current density in the effective light-emitting area when <mml:math display="inline"><mml:mrow><mml:mi>L</mml:mi><mml:mo>=</mml:mo><mml:mn>500</mml:mn><mml:mspace width="0.5em"></mml:mspace><mml:mi>μ</mml:mi><mml:mi mathvariant="normal">m</mml:mi></mml:mrow></mml:math>L=500μm . A more uniform temperature distribution in the active layer occurs when <mml:math display="inline"><mml:mrow><mml:mi>L</mml:mi><mml:mo>=</mml:mo><mml:mn>200</mml:mn><mml:mspace width="0.5em"></mml:mspace><mml:mi>μ</mml:mi><mml:mi mathvariant="normal">m</mml:mi></mml:mrow></mml:math>L=200μm , while the case when <mml:math display="inline"><mml:mrow><mml:mi>L</mml:mi><mml:mo>=</mml:mo><mml:mn>300</mml:mn><mml:mspace width="0.5em"></mml:mspace><mml:mi>μ</mml:mi><mml:mi mathvariant="normal">m</mml:mi></mml:mrow></mml:math>L=300μm has the maximum WPE.

We present a heterodyne grating interferometer based on a quasi-common-optical-path (QCOP) design for a two-degrees-of-freedom (DOF) straightness measurement. Two half-wave plates are utilized to rotate the polarizations of two orthogonally polarized beams. The grating movement can be calculated by measuring the phase difference variation in each axis. The experimental results demonstrate that our method has the ability to measure two-DOF straightness and still maintain high system stability. The proposed and demonstrated method, which relies on heterodyne interferometric phase measurement combined with the QCOP configuration, has the advantages of high measurement resolution, relatively straightforward operation, and high system stability.