Gallium nitride (GaN)

A wide-bandgap semiconductor used in laser diodes and light emitting diodes (LEDs), GaN is gaining additional importance in high-power, high-frequency applications. Photoluminescence (PL) mapping is a powerful technique to discover defects that can limit lifetime and performance. Here we demonstrate PL mapping of an off-the-shelf, GaN-based LED.

Measurements were taken with a Klar Mini Pro instrument using the 355 nm excitation kit. (The 405 nm kit also gives great results). Even though the device had an epoxy cap over the active layer, the Klar Mini Pro had no trouble obtaining high-resolution images.

A PL spectrum was collected at each (x,y) point. An example is shown in the figure. Peaks corresponding to the InGaN quantum well (QW) layer and defects are indicated. Using KlarFit, the peaks in each spectrum were fit to Gaussian functions.

To produce a PL map, the intensity and peak energy (eV) were plotted over the entire device. Very small variations in QW emission energy (upper right image) can be detected.