Impact of etching process and surface recombination on the performance of GaAs light-emitting diodes

Abstract

The quantum efficiency performance of GaAs-based light emitting diodes (LEDs) can be visibly degraded by its surface recombination. One of the detrimental influencing factors is the presence of surface defects. Especially when an LED has a high surface-to-volume ratio, the injection of carriers is strongly is weakened by the surface defects on sidewalls. There are two etching techniques to define the mesa of LED. Wet etching has equivalent vertical and horizontal etch rates, forming visible undercutting and undulating wall profiles. Dry etching, referring to reactive ion etching (RIE) used in the thesis, provides more regular profiles but may cause harmful plasma damage. Here, two GaAs/AlGaAs/InGaP double heterojunction (DHJ) LEDs were processed by wet and dry etching respectively. They were characterized with current-voltage (IV) measurements and scanning electron microscope (SEM) to compare the electrical properties and surface topography with each other.

The results confirm that the surface recombination is not negligible for small size LEDs. Dry etching generates a higher surface current associated with non-radiative recombination. Particularly, the calculated perimeter current density J02P increases by 142%. J02 contributes to the total LED current at low bias (<1.0 V). According to the previous studies, higher J02 means higher leakage current on the surface and lower internal quantum efficiency (IQE). It is demonstrated by SEM that wet etching produced visible lateral etching on the InGaP layers. Dry etching formed more uniform sidewalls but generated more rough fissures. The devices are required to be exposed to plasma, producing more unwanted surface defects. Therefore, although dry etching can avoid lateral etching, a higher leakage current was observed due to the larger surface area exposed to plasma. Wet etching is more advantageous than dry etching for GaAs-based LEDs in a small size (e.g., 250 micrometer).