Effects of InAlN underlayer on deep traps detected in near-UV InGaN/GaN single quantum well light-emitting diodes

Abstract

Two types of near-UV light-emitting diodes (LEDs) with an InGaN/GaN single quantum well (QW) differing only in the presence or absence of an underlayer (UL) consisting of an InAlN/GaN superlattice (SL) were examined. The InAlN-based ULs were previously shown to dramatically improve internal quantum efficiency of near-UV LEDs, via a decrease in the density of deep traps responsible for nonradiative recombination in the QW region. The main differences between samples with and without UL were (a) a higher compensation of Mg acceptors in the p-GaN:Mg contact layer of the sample without UL, which correlates with the presence of traps with an activation energy of 0.06 eV in the QW region, (b) the presence of deep electron traps with levels 0.6 eV below the conduction band edge (Ec) (ET1) and at Ec 0.77 eV (ET2) in the n-GaN spacer underneath the QW, and the presence of hole traps (HT1) in the QW, 0.73 eV above the valence band edge in the sample without UL (no traps could be detected in the sample with UL), and (c) a high density of deep traps with optical ionization energy close to 1.5 eV for the LEDs without UL. Irradiation with 5 MeV electrons led to a strong decrease in the electroluminescence (EL) intensity in the LEDs without UL, while for the samples with UL, such irradiation had little effect on the EL signal at high driving current, although the level of driving currents necessary to have a measurable EL signal increased by about an order of magnitude. This is despite the 5 times higher starting EL signal of the sample with UL. Irradiation also led to the appearance in the LEDs with UL of the ET1 and HT1 deep traps, but with concentration much lower than without the UL, and to a considerable increase in the Mg compensation ratio.

Effects of 5 MeV electron irradiation on deep traps and electroluminescence from near-UV InGaN/GaN single quantum well light-emitting diodes with and without InAlN superlattice underlayer

“…Both the decreased lifetime and the increased leakage are expected to contribute to the decrease of Voc [35]). In addition, the series resistance of the LED without the underlayer was found to be 2.4 times higher than for the sample with the underlayer which, as shown in our earlier paper [28], is one of the consequences of the stronger compensation of Mg acceptors in p-GaN emitter by VN-related donors that propagate from the n-type part of the structure during growth.…”

“…[24]. Such detailed DLTS studies of the LEDs with InAlN SL ULs showed [28] no detectable concentrations of electron or hole traps either in the QW or in the UL region, in contrast to structures without the UL in which electron traps with levels near Ec-0.6 eV and Ec-0.8 eV were seen in the GaN underlayer, and hole traps with levels near Ev+0.75 eV were detected in the QW, together with traps with optical ionization threshold of 1.5 eV in LCV spectra. Irradiation with a low fluence of 7×10 15 cm -2 of 5 MeV electrons had little effect on the density of traps in DLTS, but increased the density of the traps with the optical ionization threshold energy of 1.5 eV in LCV spectra of the sample without the UL while seriously decreasing the EL efficiency of such samples.…”

Defects and Reliability of GaN‐Based LEDs: Review and Perspectives

“…A good alternative is the use of AlInN UL, because with a bandgap of %4.6 eV it would ensure transparency in the NUV range, as well as the possibility to implement thinner layers, owing to the greater In content (a molar fraction of 17% is required to obtain a good lattice matching with GaN layers). [83][84][85] The adoption of AlInN UL can strongly improve the efficiency of NUV LEDs, but still presents some drawbacks. First of all, the AlInN material quality rapidly degrades as the layer thickness is increased.…”

Composition Inhomogeneity in Nonpolar (101̅0) and Semipolar (202̅1) InAlN Layers Grown by Plasma-Assisted Molecular Beam Epitaxy

“…In particular, high interest is devoted to InAlN of ≈18% In content because it is in-plane lattice-matched to (0001) GaN . Moreover, InAlN of this particular composition offers a significant refractive index and band gap contrast, which makes it an ideal candidate for cladding layers in lasers, distributed Bragg reflectors, , or transistors. , InAlN and its superlattices with GaN are also effectively used as underlayers to trap point defects and increase the efficiency of the quantum wells grown above. , …”

“…5,6 InAlN and its superlattices with GaN are also effectively used as underlayers to trap point defects and increase the efficiency of the quantum wells grown above. 7,8 Since early 2000s, there is an increasing interest in nitride structures on nonpolar and semipolar surfaces. 9−11 Removal or reduction of the polarization field, related to the substrate surface crystallographic orientation with respect to the c-axis, is expected to improve several device properties such as the radiative efficiency, optical gain, and charge transport and potentially solve problems of efficiency droop and the green gap.…”