Abstract
In this paper, we report on a detailed spectroscopic study of the optical properties of InGaN/GaN multiple quantum well structures, both with and without a Si-doped InGaN prelayer. In photoluminescence and photoluminescence excitation spectroscopy, a 2nd emission band, occurring at a higher energy, was identified in the spectrum of the multiple quantum well structure containing the InGaN prelayer, originating from the first quantum well in the stack. Band structure calculations revealed that a reduction in the resultant electric field occurred in the quantum well immediately adjacent to the InGaN prelayer, therefore leading to a reduction in the strength of the quantum confined Stark effect in this quantum well. The partial suppression of the quantum confined Stark effect in this quantum well led to a modified (higher) emission energy and increased radiative recombination rate. Therefore, we ascribed the origin of the high energy emission band to recombination from the 1st quantum well in the structure. Study of the temperature dependent recombination dynamics of both samples showed that the decay time measured across the spectrum was strongly influenced by the 1st quantum well in the stack (in the sample containing the prelayer) leading to a shorter average room temperature lifetime in this sample. The room temperature internal quantum efficiency of the prelayer containing sample was found to be higher than the reference sample (36% compared to 25%) which was thus attributed to the faster radiative recombination rate of the 1st quantum well providing a recombination pathway that is more competitive with non-radiative recombination processes.
Highlights
InGaN/GaN multiple quantum well (MQW) active regions grown on c-plane substrates are widely used in efficient light emitting diodes (LEDs).[1,2,3] The high recombination efficiencies of these InGaN/GaN QWs occur despite high densities of extended crystal defects[4–6] and the large built-in electric fields perpendicular to the plane of the QWs.[7–9] These electric fields result in a spatial separation of the electron and hole wavefunctions, leading to a reduction in the radiative recombination rate and an associated Quantum Confined Stark Effect (QCSE)
The room temperature internal quantum efficiency of the prelayer containing sample was found to be higher than the reference sample (36% compared to 25%) which was attributed to the faster radiative recombination rate of the 1st quantum well providing a recombination pathway that is more competitive with nonradiative recombination processes
intentionally Si-doped (In) this paper, we report on a detailed spectroscopic study of the optical properties of InGaN/GaN multiple quantum well structures, both with and without a Si-doped InGaN prelayer
Summary
Intensities at room temperature; this behaviour was ascribed to a reduction in the density of defects in the vicinity of the QWs. Takahashi et al.[23] reported that the inclusion of low temperature grown GaN and InGaN prelayers beneath InGaN/GaN single QWs resulted in an increased formation probability of “V”-defects, which are believed to create potential barriers around threading dislocations, thereby inhibiting carrier capture by these extended defects.[24]. We have shown[20,21] that the inclusion of a doped GaN or InGaN prelayer beneath a single QW leads to a large blue shift of the PL peak emission energy and a significant reduction in the low temperature (10 K) PL decay time at the PL peak, compared to a single QW structure grown without a prelayer. In light of this recent work, we have extended our investigations of InGaN MQWs with prelayers to include further PL excitation (PLE) spectroscopy and a detailed temperature dependent timeresolved spectroscopic study of the optical properties of InGaN MQWs with and without prelayers
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