Local carrier recombination and associated dynamics in m-plane InGaN/GaN quantum wells probed by picosecond cathodoluminescence

Abstract

We report on spatially resolved and time-resolved cathodoluminescence (CL) studies of the recombination mechanisms of InGaN/GaN quantum wells (QWs) grown by metal-organic vapour phase epitaxy on bulk m-plane Ammono GaN substrates. As a result of the 2° miscut of the GaN substrate, the sample surface exhibits step bunches, where semi-polar QWs with a higher indium concentration than the planar m-plane QWs form during the QW growth. Spatially resolved time-integrated CL maps under both continuous and pulsed excitation show a broad emission band originating from the m-plane QWs and a distinct low energy emission originating from the semi-polar QWs at the step bunches. High resolution time-resolved CL maps reveal that when the m-QWs are excited well away from the step bunches the emission from the m-plane QWs decays with a time constant of 350 ps, whereas the emission originating semi-polar QWs decays with a longer time constant of 489 ps. The time constant of the decay from the semi-polar QWs is longer due to the separation of the carrier wavefunctions caused by the electric field across the semi-polar QWs.

Photon bunching reveals single-electron cathodoluminescence excitation efficiency in InGaN quantum wells

“…In CL, a high-energy electron beam in a scanning electron microscope (SEM) excites a material and generates luminescence that is collected and analyzed. CL emission gives valuable spatially resolved information about the band gap [7,8], carrier generation [9], defects [10,11], diffusion and carrier transport [12][13][14], recombination [15,16], and other optoelectronic properties of semiconductors that are used, e.g., in light-emitting diodes (LEDs) [17,18], lasers [19], solar cells [20], and more.…”

Spatially and Time-Resolved Carrier Dynamics in Core–Shell InGaN/GaN Multiple-Quantum Wells on GaN Wire

“…In good agreement with Figure , the decay times collected from sidewalls are generally shorter than the ones taken from the top facet. The fast characteristic time of about τ short ∼ 100 ps is typical of nonpolar and semipolar MQWs, where the reduced QCSE enables more efficient radiative transitions . If the assumptions of Lin et al are valid (namely, the slow and fast decay times are connected to local indium fluctuations and InGaN thickness variations, respectively), , then our findings would suggest that in comparison to mild well thickness fluctuations (τ short ), in the top surface, there are more significant In inhomogeneities (τ long ) than in the sidewalls.…”

“…The fast characteristic time of about τ short ∼ 100 ps is typical of nonpolar and semipolar MQWs, where the reduced QCSE enables more efficient radiative transitions. 57 If the assumptions of Lin et al are valid (namely, the slow and fast decay times are connected to local indium fluctuations and InGaN thickness variations, respectively), 52,53 then our findings would suggest that in comparison to mild well thickness fluctuations (τ short ), in the top surface, there are more significant In inhomogeneities (τ long ) than in the sidewalls. In addition, the short decay times are faster at the two vertices of the top surface, indicating a larger overlapping of the wave functions of the electrons and holes, which is consistent with their higher integrated XEOL intensity.…”

Uncovering the carrier dynamics of AlInGaN semiconductors using time-resolved cathodoluminescence

“…Hence 'charge carrier dynamics' describes the motion and activity of excess electrons and holes in a semiconductor from the point they are generated to when they recombine. An in-depth appreciation of the charge carrier dynamics in semiconductors is key to unravelling a multitude of phenomena such as the density, type and behaviour of structural imperfections (defects), the presence and magnitude of inherent polarisation fields and how they relate to the crystal structure, charge carrier transport, and recombination channels [23][24][25][26][27].…”