GaN Light-Emitting Triodes (LETs) for High-Efficiency Hole Injection and for Assessment of the Physical Origin of the Efficiency Droop

摘要

The light-emitting triode (LET) is a three-terminal p-n junction device that accelerates carriers in the lateral direction, i.e. parallel to the p-n junction plane, by means of an electric field between two anodes. The lateral field provides additional energy to carriers thereby allowing them to overcome barriers and increasing the carrier injection efficiency into the active region. Both the current between Anode 1 and the cathode, and the light- output power increase with increasing negative bias to the Anode 2. This is consistent with the expectation that a negative bias to the second anode allows carriers to acquire a high kinetic energy thereby enabling them to overcome the barrier for holes, resulting in high injection efficiency into the active region that lies beyond the barrier. In addition, we have proposed an innovative approach that allows us to investigate the relationship between the hole-injection efficiency and the efficiency droop by using the LET (the efficiency droop is the decrease in efficiency of III-V nitride pn-junction devices with increasing injection current). Our simulation reveals that the electron overflow into the p-type GaN cladding layer, caused by low hole- injection efficiency into the MQW active region, is the origin of the efficiency droop. Therefore, the LET, in which the hole-injection efficiency can be controlled by the bias to the second anode, can be an effective method to investigate the physical origin of the efficiency droop. We believe that our research has been highly successful because it has allowed us to analyze and identify the origin of the efficiency droop in III-V nitride pn junction devices. Since this is known to be a major problem, the resolution of this problem is a major step forward in the development of III-V emitter technology including UV emitter technology.