GaN-Based Bipolar Cascade Lasers with 25nm Wide Quantum Wells

Utilizing self-consistent numerical simulation in good agreement with measurements, we analyze internal device physics, performance limitations, and optimization options for a unique laser design with multiple active regions separated by tunnel junctions, featuring surprisingly wide InGaN quantum wells. Contrary to common assumptions, these quantum wells are revealed to allow for perfect screening of the strong built-in polarization field, while optical gain is provided by higher quantum levels. However, internal absorption, low p-cladding conductivity, and self-heating are shown to strongly limit the laser performance.

III-nitride optoelectronic devices containing wide quantum wells - unexpectedly efficient light sources

In this paper we review the recent studies on wide InGaN quantum wells (QWs). InGaN QWs are known to suffer from an extremely high built-in piezoelectric polarization, which separates the electron and hole wavefunctions and causes the quantum-confined Stark effect. It is shown, both by means of modeling and experimentally, that wide InGaN QWs can have quantum efficiency superior to commonly used thin QWs. The high efficiency is explained by initial screening of the piezoelectric field and subsequent emergence of optical transitions involving the excited states of electrons and holes, which have a high oscillator strength. A high pressure spectroscopy and photocurrent measurements are used to verify the mechanism of recombination through excited states. Furthermore, the influence of QW width on the properties of optoelectronic devices is studied. In particular, it is shown how the optical gain forms in laser diodes with wide InGaN QWs.