Abstract
AbstractWe report on the effects of varying the number of quantum wells (QWs) in an InGaN/GaN multiple QW (MQW) structure containing a 23 nm thick In0.05Ga0.95N prelayer doped with Si. The calculated conduction and valence bands for the structures show an increasing total electric field across the QWs with increasing number of QWs. This is due to the reduced strength of the surface polarisation field, which opposes the built‐in field across the QWs, as its range is increased over thicker samples. Low temperature photoluminescence (PL) measurements show a red shifted QW emission peak energy, which is attributed to the enhanced quantum confined Stark effect with increasing total field strength across the QWs. Low temperature PL time decay measurements and room temperature internal quantum efficiency (IQE) measurements show decreasing radiative recombination rates and decreasing IQE, respectively, with increasing number of QWs. These are attributed to the increased spatial separation of the electron and hole wavefunctions, consistent with the calculated band profiles. It is also shown that, for samples with fewer QWs, the reduction of the total field across the QWs makes the radiative recombination rate sufficiently fast that it is competitive with the efficiency losses associated with the thermal escape of carriers. (© 2016 The Authors. Phys. Status Solidi C published by WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Highlights
InGaN/GaN quantum wells (QWs) are regularly incorporated in the active regions of highefficiency blue light emitting diodes (LEDs)
The calculated total electric field across the QWs in each structure was found to increase with increasing number of QWs, due to the reduced strength of the surface polarisation field with increasing separation between the prelayer and the GaN/air interface
We measured a red shift in the (M)QW PL emission energy and a decrease in the radiative recombination rate with increasing number of QWs
Summary
InGaN/GaN quantum wells (QWs) are regularly incorporated in the active regions of highefficiency blue light emitting diodes (LEDs). There have been several reports [3,4,5,6,7,8,9,10,11,12,13] that the growth of a layer of InGaN, 10s of nm thick and referred to as a prelayer, prior to the first QW in multiple QW (MQW) structures and LEDs leads to increases in the measured luminescence intensity and room temperature (RT) internal quantum efficiency (IQE). Suggestions for the mechanism by which prelayers bring about these improvements have included strain reduction in the QW layers [3], acting as an “electron reservoir” from which carriers tunnel into the QWs [4], and a reduction in the density of point defects in the active region [5,8,9,10].
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