Wurtzite quantum well structures under high pressure

Abstract

Quantum well systems based on semiconductors with the wurtzite crystalline structure have found widespread applications in photonics and optoelectronic devices, such as light-emitting diodes, laser diodes, or single-photon emitters. In these structures, the radiative recombination processes can be affected by (i) the presence of strain and polarization-induced electric fields, (ii) quantum well thickness fluctuations and blurring of a well–barrier interface, and (iii) the presence of dislocations and native point defects (intentional and unintentional impurities). A separate investigation of these phenomena is not straightforward since they give rise to similar effects, such as a decrease of luminescence efficiency and decay rate, enhancement of the Stokes shift, and strong blueshift of the emission with increasing pump intensity. In this Perspective article, we review the usefulness of measurements of the quantum well luminescence as a function of the hydrostatic pressure for both scientific research and the development of light-emitting technologies. The results presented here show that high-pressure investigations combined with ab initio calculations can identify the nature of optical transitions and the main physical factors affecting the radiative efficiency in quantum well systems. Finally, we will discuss an outlook to the further possibilities to gain new knowledge about the nature of recombination processes in quantum wells using high-pressure spectroscopy.

Hydrostatic Pressure as a Tool for the Study of Semiconductor Properties – an Example of III-V Nitrides

“…The calculated results for narrow QWs are in good agreement with the experimental data. However, for wider QWs there are discrepancies between the calculated low oscillator strengths and higher experimental decay rate [69]. The experimentally observed decay, which is too high compared to the calculations, could be due to the screening of the electric field by free carriers.…”

“…High-pressure studies, which often combine experiment and theory, can provide important results that are difficult or impossible to obtain otherwise and allow for the description of the main factors that influence radiative recombination processes and radiative efficiency. Recent studies [69,70] have shown that high pressure spectroscopy is an effective tool for analyzing factors related to strain effects, built-in electric fields, and the involvement of defect states in recombination processes in quantum heterostructures. Now we will focus on the built-in electric field (approaching a few MV/cm) present in the polar wurtzite structure of nitride heterostructures.…”

“…The strength of the built-in electric field increases with application of hydrostatic pressure [71]. To investigate the piezoelectric effects, high-pressure spectroscopy can be used based on the following relationship [69,70]:…”

Critical Evaluation of Various Spontaneous Polarization Models and Induced Electric Fields in III-Nitride Multi-Quantum Wells

“…Polarization-induced electric fields can manifest in nanometer-size heterostructures (quantum wells, wires or dots [ 7 , 8 , 9 , 10 ]) and cause a shift of the transition energy between quantum states which is known as quantum-confined Stark effect (QCSE) [ 11 , 12 ]. In some cases, polarization has a beneficial influence on the device performance, e.g., in field effect transistors (FETs) [ 13 , 14 , 15 ].…”

“…However, in optoelectronic devices, such as light-emitting diodes (LEDs) or laser diodes (LDs), the QCSE should be reduced as much as possible. Associated with the spectral shift, there is a separation of electrons and holes within the structure, which reduces the overlap of electron/hole wavefunctions and consequently the radiative recombination rate and the emission efficiency [ 9 , 10 , 11 , 12 , 16 , 17 ]. The majority of nitride-based optoelectronic devices are based on polar multi-quantum wells (MQWs), with heterointerfaces perpendicular to the polarization axis, so that polarization effects are particularly strong.…”