Room temperature PL efficiency of InGaN/GaN quantum well structures with prelayers as a function of number of quantum wells

Abstract

We 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)

Optical properties of c-Plane InGaN/GaN single quantum wells as a function of total electric field strength

“…The peak emission energy decreases by approximately 22 meV as the cap layer thickness is increased from 2 to 4 nm, and then increases by approximately 6 meV between the 4 nm and 5 nm cap layer samples. Based on our previous studies of the effects of n-type ULs on the total electric fields across QWs, 13,14) as well as our simple band-edge profile simulations described in Sect. 2.1, we expect that the total electric field across the QW in each sample decreases with decreasing total distance between the UL and the sample/air interface, i.e.…”

“…[1][2][3][4][5][6][7][8][9][10][11] From a theoretical perspective, we have previously demonstrated [1][2][3] that holes are strongly localized by random alloy fluctuations and that electrons are localized by a combination of effects due to the built-in electrostatic fields, random alloy fluctuations and well width fluctuations (WWFs). We have also previously shown experimentally [12][13][14][15] that the inclusion of a Si-doped, n-type InGaN underlayer (UL) in InGaN/GaN QW structures leads to an enhancement of the surface polarization field which acts in the opposite direction to the intrinsic electrostatic built-in fields. 16) This occurs because of the pinning of the Fermi level at the conduction band edge in the region of the n-type UL and at the valence band edge at the GaN/air interface due the large charge density formed by the discontinuity in the spontaneous polarization.…”

“…16) This occurs because of the pinning of the Fermi level at the conduction band edge in the region of the n-type UL and at the valence band edge at the GaN/air interface due the large charge density formed by the discontinuity in the spontaneous polarization. 17) Overall, this results in a reduction in the total field across the QW(s), giving rise to shorter radiative recombination lifetimes [12][13][14][15] and increased room temperature IQEs 12,13) measured for QW structures containing ULs. Although an alternative mechanism for the improvements due to ULs has been proposed whereby point defects or impurities are trapped in the UL, preventing their incorporation into the QWs, 18) other groups have reported [19][20][21] similar improvements for QW structures where the total electric field has been reduced by modifying the barrier alloy composition and/or doping concentrations, consistent with our previous experimental work.…”

“…Samples Initially, a range of single QW structures were designed using the commercial device simulator nextnano 3 . 23) Following our previous work, [12][13][14][15] the structures all contained a Si-doped InGaN UL. The built-in fields across InGaN/GaN QWs…”

Effect of Si-doped InGaN underlayers on photoluminescence efficiency and recombination dynamics in InGaN/GaN quantum wells

“…Underlayers (ULs) are regions of unintentionally-or Sidoped (In)GaN that are typically 10-20 nm in thickness and positioned a few nm below the QWs. ULs are of interest because their incorporation into device structures has been found to improve the IQE of QWs [11,12]. Initial work on doped ULs found that they increase the radiative recombination rate by reducing the net electric field across the QWs [11,12].…”