Tech Briefs

Efficiency droop, heretofore observed in ultraviolet lightemitting diodes, can be overcome.

Light-emitting triodes (LETs) have been the focus of a program of research with a goal of increasing the quantum efficiencies of ultraviolet-lightemitting devices implemented in the AlxInyGa1-x-yN (0 ≤ x+y ≤ 1) material system. Heretofore, AlxInyGa1-x-yN-based light-emitting diodes (LEDs) have exhibited "efficiency droop" — decreasing quantum efficiency with increasing injection current. LETs can be used as means of studying and overcoming efficiency droop.

Figure 1. These Energy-Band Diagrams are typical of two alternative structures of AlxInyGa1-x-yN-based ultraviolet LEDs.
Figure 1 depicts relevant aspects of two alternative structures typical of AlxInyGa1- x-yN-based ultraviolet LEDs. In one structure, an electron blocking layer (EBL) is inserted between an electron-acceptortype (p-type) cladding layer and a multiple- quantum-well (MQW) active region. The EBL serves to prevent the overflow of electrons from (and thereby confine electrons to) the active region. If the EBL is heavily p-doped, then it does not impede the injection of holes into the active region. However, depending upon the chemical composition of the specific LED, heavy p-doping of the EBL is not possible, in which case, in addition to confining electrons to the active region, the EBL also constitutes a potential barrier for holes, hindering injection of holes into the active region and thereby limiting the internal quantum efficiency.