Physics and polarization characteristics of 298 nm AlN-delta-GaN quantum well ultraviolet light-emitting diodes

Liu, Cheng; Ooi, Yu Kee; Islam, S. M.; Verma, Jai; Xing, Huili Grace; Jena, Debdeep; Zhang, Jing

doi:10.1063/1.4976203

Cited by 47 publications

(52 citation statements)

References 29 publications

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“…112, 011101-1 (QCSE), which is addressed by the use of the AlN-delta-GaN QW as the electron and hole wavefunction overlap can be improved significantly. 19 When the wavelengths are pushed to the shorter regime (<250 nm), the band mixing effect due to the existence of the valence subband crossover becomes the dominant challenge. The delta-QW design can be a promising solution to address this issue as a large separation between ground states of HH (HH1) and CH (CH1) at the C-point is expected.…”

Section: B)mentioning

confidence: 99%

“…Therefore, the AlN sub-QW and AlN barrier are separately considered in the 6-band kÁp calculations. 19 The thicknesses of the delta-GaN layer are selected to be 3 Å and 4 Å to achieve 232 nm and 243 nm emissions, respectively, while the AlN sub-QW is designed to be 2 nm. Here, the use of the AlN-delta-GaN QW structure is aimed to address the severe valence band mixing issue at sub 250 nm so that the HH subband can be clearly separated from the CH subband to ensure dominant C-HH transition.…”

Section: B)mentioning

confidence: 99%

“…18 On the other hand, our previous work demonstrated AlNdelta-GaN QW with 3-4 monolayers (MLs) of delta-GaN emitting at 298 nm, which can be achieved with straightforward epitaxial growths. 19 The main challenge at $298 nm from AlGaN QW is the quantum-confined Stark effect a)…”

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confidence: 99%

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234 nm and 246 nm AlN-Delta-GaN quantum well deep ultraviolet light-emitting diodes

Liu

Ooi

Islam

et al. 2018

Applied Physics Letters

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Deep ultraviolet (DUV) AlN-delta-GaN quantum well (QW) light-emitting diodes (LEDs) with emission wavelengths of 234 nm and 246 nm are proposed and demonstrated in this work. Our results reveal that the use of AlN-delta-GaN QW with $1-3 monolayer GaN delta-layer can achieve a large transverse electric (TE)-polarized spontaneous emission rate instead of transverse magneticpolarized emission, contrary to what is observed in conventional AlGaN QW in the 230-250 nm wavelength regime. The switching of light polarization in the proposed AlN-delta-GaN QW active region is attributed to the rearrangement of the valence subbands near the C-point. The light radiation patterns obtained from angle-dependent electroluminescence measurements for the Molecular Beam Epitaxy (MBE)-grown 234 nm and 246 nm AlN-delta-GaN QW LEDs show that the photons are mainly emitted towards the surface rather than the edge, consistent with the simulated patterns achieved by the finite-difference time-domain modeling. The results demonstrate that the proposed AlN-delta-GaN QWs would potentially lead to high-efficiency TE-polarized surface-emitting DUV LEDs.

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Section: B)mentioning

confidence: 99%

Section: B)mentioning

confidence: 99%

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234 nm and 246 nm AlN-Delta-GaN quantum well deep ultraviolet light-emitting diodes

Liu

Ooi

Islam

et al. 2018

Applied Physics Letters

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“…As a significant advantage, the polarization of the emitted photons in ultrathin GaN QWs and quantum dots/disks (QDs) is perpendicular to the c axis, making them propagate parallel to the c-axis [9,11]; this surface emission property is highly favorable for light extraction.…”

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confidence: 99%

Deep-UV emission at 219 nm from ultrathin MBE GaN/AlN quantum heterostructures

Islam

Protasenko

Lee

et al. 2017

Applied Physics Letters

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The ruggedness, portability, high-efficiency, and microfabrication benefits of solid-state semiconductor light sources over conventional lamps became clear in the last decade for visible wavelengths in the solid-state lighting revolution, and gave birth to several new applications. A similar revolution is expected in the deep-UV spectrum. Semiconductor light sources such as Light-Emitting Diodes (LEDs) and Lasers in the deep ultraviolet (UV) spectrum have versatile applications in water and air purification, in healthcare applications of biophotonic diagnostics and sterilization, in food preservation, in security and environmental monitoring and in industrial curing. The semiconductor material substrate of choice for deep-UV photonic devices is direct-bandgap AlN with an energy bandgap of ~6.2 eV (200 nm), and the active regions where photons are produced are various ternary compositional alloys of AlN with GaN of bandgap ~3.4 eV (365 nm).For deep-UV LEDs, quantum well active regions composed of AlGaN have been used to push the interband optical transition to high energies [1][2][3][4][5]. The internal quantum efficiency in high Al containing AlGaN Quantum Wells (QWs)/barrier structures is limited by the quantum confined stark effect (QCSE) [6][7][8], edge emission due to valence band structure re-ordering [9][10][11], combined with material defect (e.g. dislocation) induced non-radiative recombination. Compositional fluctuations of Al and Ga concentrations in ternary AlGaN alloy layers degrade efficient optical emission in the deep-UV range [12], and together with the other effects degrade the LED efficiency.Distinct from the alloy AlGaN layers, deep-UV emission down to 224 nm has been achieved in binary GaN/AlN heterostructures [13][14][15][16][17]. As a significant advantage, the polarization of the emitted photons in ultrathin GaN QWs and quantum dots/disks (QDs) is perpendicular to the c axis, making them propagate parallel to the c-axis [9,11]; this surface emission property is highly favorable for light extraction.We recently demonstrated deep UV LEDs [18-20] emitting as short as 232 nm by incorporating 2 monolayer (ML) thick GaN QDs in AlN barriers. As the height of the QD reduces and the oscillator strength increases [21], the radiative lifetime decreases significantly, increasing the internal quantum efficiency. Shortening the emission wavelength even deeper below 230 nm by utilizing GaN QDs embedded in AlN barriers will further enable applications in sensing and toxic gas detection applications. Tunable sub-230 nm deep-UV emission was demonstrated by Molecular Beam Epitaxy (MBE) growth of 2 ML GaN QDs using a modified Stranski-Krastanov (m-SK) growth method [22]. The m-SK technique uses thermal annealing of the 2 ML GaN quantum well structure sandwiched between AlN barriers. In this letter, we present an alternative approach to realize tunable sub-230 nm emission with higher internal quantum efficiency using SK growth of 2 ML GaN QD structures by MBE. Unlike the earlier work based on m-SK method, cont...

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“…Till now, several consents have been reached to take account for the IQE of DUV LEDs. The lattice and thermal mismatches between the Al‐rich layers and the sapphire substrate lead to a very high threading dislocation density (TDD) that is in the order of 10 9 –10 10 cm −2 for the epi‐layer, which remarkably affects the IQE. The intrinsic IQE measured by using the low‐temperature photoluminescence method can reach as high as 80% as long as the TDD is smaller than 1 × 10 8 cm −2 .…”

Section: Materials Parameters Used For Numerically Calculating Wurtzitmentioning

confidence: 99%

Investigations on AlGaN‐Based Deep‐Ultraviolet Light‐Emitting Diodes With Si‐Doped Quantum Barriers of Different Doping Concentrations

Tian

Chang

Chu

et al. 2017

Physica Rapid Research Ltrs

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In this work, we investigate the impact of Si doped AlGaN quantum barriers on the optical powers for [0001] oriented III-nitride based deep-ultraviolet light-emitting diodes (DUV LEDs). The polarization-induced electric field in the active region is screened as the result of Si-doped quantum barriers, which gives rise to the improved spatial overlap between electron and hole wave functions. The polarization screening effect within the quantum wells is further proven by the observation of the blue shift for the wavelength. However, the hole distribution across the active region can be significantly retarded if the Si dosage in the quantum barriers is too high. Therefore, the improved radiative recombination within the active region can be realized provided that the Si dosage in the quantum barriers is moderately adjusted to guarantee both the better hole injection efficiency and the screened polarization effect in the multiple quantum wells.III-nitride based deep-ultraviolet light-emitting diodes (DUV LEDs) have presented great application potentials in water sterilization, medical therapy, biochemical agent detection, [1,2] and thus they have drawn significant attention accordingly. The excellence of DUV LEDs is partly justified by the internal quantum efficiency (IQE). Till now, several consents have been reached to take account for the IQE of DUV LEDs. The lattice and thermal mismatches between the Al-rich layers and the sapphire substrate lead to a very high threading dislocation density (TDD) that is in the order of 10 9 -10 10 cm À2 for the epi-layer, [3][4][5][6] which remarkably affects the IQE. The intrinsic IQE measured by using the low-temperature photoluminescence method can reach as high as 80% as long as the TDD is smaller than 1 Â 10 8 cm À2 . [7] DUV LEDs are normally driven electrically and hence the IQE is also strongly subject to the hole injection. The activation energy of Mg acceptors becomes even higher for Al-rich p-AlGaN layers, [8] and this correspondingly causes an insufficient hole concentration as well as a low hole injection efficiency for DUV LEDs. Therefore, one shall not substantially sacrifice the hole injection when designing novel structures. The nature of the wurtzite structure causes the crystal asymmetry, which results in the very strong internal polarization effect for AlGaN/AlGaN multiple quantum wells (MQWs) grown along the [0001] orientation. The polarization induced electric field within the MQWs can cause a spatial separation of carrier wave functions and reduces the emission efficiency, which is known as the quantum-confined Stark effect (QCSE). [9,10] To mitigate the QCSE in [0001] oriented lattice-mismatched quantum wells, it is promising to adopt polarization matched AlInGaN quantum barriers for the active region. [11] Alternatively, the polarization effect within the quantum wells can be screened by grading the alloy composition of the quantum barriers [9] or the quantum wells. [12] Among all the approaches, the most convenient method to screen the polarization...

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Physics and polarization characteristics of 298 nm AlN-delta-GaN quantum well ultraviolet light-emitting diodes

Cited by 47 publications

References 29 publications

234 nm and 246 nm AlN-Delta-GaN quantum well deep ultraviolet light-emitting diodes

234 nm and 246 nm AlN-Delta-GaN quantum well deep ultraviolet light-emitting diodes

Deep-UV emission at 219 nm from ultrathin MBE GaN/AlN quantum heterostructures

Investigations on AlGaN‐Based Deep‐Ultraviolet Light‐Emitting Diodes With Si‐Doped Quantum Barriers of Different Doping Concentrations

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