The properties of III-nitride quantum wells (QWs) are significantly affected by polarization fields. We show that, in the case of wide QWs, there exist two fundamentally different transition types characterized by quantum-confinement effects or bulklike behavior—depending on the carrier density in the structure. At low carrier density, spontaneous and piezoelectric polarization lead to tight confinement and low spatial overlap between the electron and hole wave functions. However, if the carrier density is sufficient for screening of the polarization fields, the wave functions spread out, reach high overlap, and the energy states come close to each other, similar to a bulk semiconductor. Streak camera measurements in the subthreshold regime of nitride laser diodes and numerical simulations show consistent results and let us clearly differentiate between contributions of individual states for low carrier density and the emergence of a high density of energetically close states at high carrier density.

In group‐III‐nitride quantum wells (QWs), a strong piezoelectric field is formed. A built‐in potential from the p–n junction is working in the opposite direction depending on an externally applied voltage. Furthermore, the electric field in the QW can be partially screened by a high charge carrier density. Herein, the influence of these effects on recombination and spectrum for over 10 nm wide InGaN QWs is investigated. The very low overlap of electrons and holes would suggest inefficient devices. However, it is shown that thick QWs can be more effective and reach high optical gain. This can be explained by the screening of the electric field, resulting in a high overlap of excited electron and hole states that enable lasing. Herein, a pulsed electrical excitation scheme is used, where carrier injection at forward bias and predominant recombination at zero or reverse bias are separated in time. The interplay between the piezoelectric field and the built‐in potential on carrier recombination in dependence on an external bias voltage is observed. In particular, a strong increase of the radiative recombination rate after the trailing edge of the driving pulse is observed.

In nitride‐based laser diodes, the poor conductivity of the p‐type region, higher light absorption, and the difficult processing of an ohmic p‐contact with low resistance are major challenges. Recently interband tunnel junctions (TJs) have been used to replace much of the hole transport layers by electron transport layers, and also to allow for two n‐type contacts. In this work, GaN‐based laser diode stacks with TJs are analyzed. The devices are grown with plasma‐assisted molecular beam epitaxy and include two waveguides with active regions consisting of 25 nm wide InGaN quantum well (QW), each, which are connected through a TJ. A second TJ is placed on top to eliminate the p‐type contact. In this study, the time‐dependent spectral behavior of such structures is analyzed by streak camera measurements. The two QWs have different lasing thresholds and emission wavelength. Using the temporal resolution of the streak camera, a lasing onset of the second QW a few nanoseconds after the first one is observed. Single shot measurements show unusual intensity oscillations from both QWs, however, one is stable and the other laser diode (LD) has irregular oscillations.

Low-temperature photoluminescence (PL) has been studied under hydrostatic pressure and varying excitation powers in three samples of single In_0.17Ga_0.83N quantum wells with different widths: 2.6 nm, 5.2 nm, and 10.4 nm. Transitions involving ground states were strong in the 2.6 nm well, weak in the 5.2 nm well, and absent in the 10.4 nm well. Pressure coefficients of PL lines have been used to estimate the electric field in the wells. In the widest well, the field seems to be fully screened (at high excitation powers). Simulations involving Poisson and Schrödinger equations allowed us to identify the experimental PL lines. Pressure evolution of the PL spectra agreed with the simulation. We present diagrams showing the dependence of the field in the well on pressure and on carrier concentration. In wide wells, these diagrams illustrate the transition from a 2D-like system to a 3D-like system.

Low temperature photoluminescence (PL) has been studied under hydrostatic pressure and under varying excitation powers in three samples of single In0.17Ga0.83N quantum wells with different widths: 2.6 nm, 5.2 nm, and 10.4 nm. Transitions involving ground states were strong in the 2.6 nm well, weak in the 5.2 nm well, and absent in the 10.4 nm well. Pressure coefficients of PL lines have been used to estimate the electric field in the wells. In the widest well the field seems to be fully screened (at high excitation powers). Simulations involving Poisson and Schrodinger equations allowed to identify the experimental PL lines. Pressure evolution of the PL spectra agreed with the simula-tion.