GaN surface as the source of non-radiative defects in InGaN/GaN quantum wells

Abstract

Blue light-emitting diodes based on III-nitride semiconductors are nowadays widely used for solid-state lighting. They exhibit impressive figures of merit like an internal quantum efficiency close to 100%. This value is intriguing when considering the high dislocation density running throughout the InGaN/GaN quantum well (QW) active region. This striking feature is currently ascribed to carrier localization occurring in the InGaN alloy, which hinders their diffusion toward dislocations. However, it was recently reported that another source of defects, disconnected from dislocations, dramatically decreases the radiative efficiency of InGaN/GaN QWs. Those defects, present at the surface, are usually trapped in an InGaN underlayer (UL), which is grown before the QW active region. To get insight into the trapping mechanism, we varied the UL thickness, In content, and materials system (InGaN or InAlN) and studied the photoluminescence decay time at 300 K of a single InGaN/GaN QW. Our data demonstrate that defects are incorporated proportionally to the indium content in the UL. In addition, we show that those defects are created during the high-temperature growth of GaN and that they segregate at the surface even at low-temperature. Eventually, we propose an intrinsic origin for these surface defects.

Deep‐Level Defects and Impurities in InGaN Alloys

“…However, the efficiency of long‐wavelength InGaN devices is hampered by several challenges, one of which is the unintentional incorporation of point defects that act as a source of carrier recombination . Indeed, a number of experimental studies have identified the presence of deep defects in InGaN layers and have alluded to point defects as a source of efficiency reduction in InGaN optoelectronic devices . Identifying the microscopic origin of defects in an InGaN alloy is complicated as the defect levels are likely to exhibit different sensitivities to changes in the In concentration, InGaN bandgap and band edges, and distribution of In and Ga cations.…”

Quantum Efficiency of III-Nitride Emitters: Evidence for Defect-Assisted Nonradiative Recombination and its Effect on the Green Gap

“…We study samples with 4 nm-thick single-QWs within p-i-n regions, grown on c-plane bulk GaN substrates by MOCVD; these samples include an InGaN underlayer (UL) beneath the p-i-n region, which improves material quality [10][11][12]. Importantly, the QW is placed at the center of the intrinsic region to avoid modulation-doping, which would alter the recombination dynamics [13].…”

Influence of an InGaN superlattice pre-layer on the performance of semi-polar (11–22) green LEDs grown on silicon

“…Based on previous studies, point defects such as nitrogen vacancies or surface point defects generated during high temperature growth of GaN layer can be captured by a low-temperature grown InGaN pre-layer [8][9][10] . As a result, the performance of the semi-polar (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) LEDs with the SLS pre-layer can be improved due to a reduction in point defect density.…”

“…It is also well-known that it is crucial to insert a single InGaN underlayer or an InGaN/GaN superlattice structure (SLS) as a pre-layer prior to the growth of InGaN/GaN multiple quantum wells (MQWs) as an emitting region in an LED. The performance of the III-nitride LEDs are then dramatically improved [2][3][4][5][6][7][8][9][10] , although the pre-layer is typically grown at a low temperature which generates extra defects [8][9][10] . Furthermore, even for the growth on GaN substrates (where the dislocation density is significantly low), III-nitride LEDs without any pre-layer exhibit much worse performance than those with a pre-layer but grown on sapphire [8][9][10] .…”

“…In order to address this issue, a number of models have been proposed to provide a mechanism for the enhanced performance of III-nitride LEDs grown with a pre-layer [2][3][4][5][6][7][8][9][10] . So far, the most convincing model identifies point defects induced by vacancies as an important additional source of NRCs [8][9][10] . Furthermore, it has been demonstrated that the density of point defects in InGaN/GaN MQWs in the active region of an LED is significantly reduced if a pre-layer is prepared prior to the growth of the active region 9 .…”