In light emitting devices based on GaN, InN, AlN and their alloys, the presence of a built-in electric field (caused by spontaneous and piezoelectric polarization effects) has a detrimental effect on the efficiency of the device. Indeed, built-in electric fields induce a spatial separation of electrons and holes in the quantum wells of the active region, thereby considerably reducing the radiative recombination rate and, ultimately, the device efficiency.
The aim of this work is the demonstration of the feasibility of high hydrostatic pressure experiments as a tool for the determination of the presence of electric fields in group III-nitride structures. Indeed, the presence of electric fields can be sensitively detected through a drastic reduction of the observed shift of the emitted light energy as a function of pressure with respect to the pressure evolution of the band gap in bulk material. This reduction can be used as a fingerprint of the presence of a built-in electric field.
In this work, we first discuss the behavior under the influence of built-in electric fields and pressure of a variety of quantum structures. After this, we proceed to a proposed design of laser diodes (grown on bulk GaN crystals) based on quantum structures with a reduced internal electric field. For that purpose the appropriate screening of the built-in electric fields by doping and/or injection of charges is applied. In these devices, we show a bulk-like value of the pressure coefficient in the high current injection regime. This result demonstrates the absence of built-in electric fields in our laser diodes, showing that the proposed laser diode design helps to avoid the detrimental effects of the presence of electric fields (such as the reduction of efficiency due to carrier separation and the reduction of laser gain). In the final part, we discuss the particular roles of electric field screening by injected carriers on one hand, and doping on the other.