The difficulties in achieving high hole concentrations in group-III nitrides originate from high values of activation energy of acceptors. The average hole concentration can be increased in a p-doped nitride superlattice (SL). However, most of the holes ionized from the acceptors are localized inside the quantum wells (QWs) and cannot participate in vertical transport utilized in traditional light-emitting devices (LEDs). In this report we propose two novel solutions of the problem of hole injection enhancement in wide band-gap LEDs.
Low-intensity emitters: The conventional LEDs can be modified by introducing a two-terminal hole injector that consists of a p-doped SL-base with two contacts. A bias voltage applied between these contacts provides lateral hole acceleration and increases the effective hole temperature. This results in significant enhancement of overbarrier hot-hole concentration. The proposed LED can be thought of as a three terminal device, where the hot-hole SL-injector is placed on the top of heterostructure with an intrinsic i-layer, and an n-doped region. In the report, we discuss parameters of the nitride-based hot-hole injectors and characteristics of the three terminal UV-LEDs.
High-intensity lateral current pumped emitters: To achieve high-density electron-hole plasma (EHP) and interband population inversion in group-III nitrides, we propose a planar p-i-n structure created in selectively-doped SLs: a region doped with acceptors is followed in lateral direction by an i-region and, finally, by an n-region. Thermal activation of the dopants supplies carriers into the QW layers. The QW layers accumulate both types of free carriers and a lateral p-i-n structure is formed.