Alternating-Current InGaN/GaN Tunnel Junction Nanowire White-Light Emitting Diodes

Sadaf, Sharif Md.; Ra, Yong–Ho; Nguyen, Hieu Pham Trung; Djavid, Mehrdad; Mi, Zetian

doi:10.1021/acs.nanolett.5b02515

Cited by 90 publications

(63 citation statements)

References 51 publications

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“…2(a)). [16][17][18][19][20][21][22] Due to the polarization discontinuity, sheet charges with density over 10 13 cm -2 are induced at the AlGaN/InGaN heterointerfaces and this reduces the tunneling barrier to less than 3 nm ( Fig. 2(b)), leading to much higher tunneling probability compared to the homojunction tunnel junction.…”

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confidence: 99%

Design and demonstration of ultra-wide bandgap AlGaN tunnel junctions

Zhang

Krishnamoorthy

Akyol

et al. 2016

Applied Physics Letters

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Ultra violet light emitting diodes (UV LEDs) face critical limitations in both the injection efficiency and light extraction efficiency due to the resistive and absorbing p-type contact layers. In this work, we investigate the design and application of polarization engineered tunnel junctions for ultra-wide bandgap AlGaN (Al mole fraction > 50%) materials towards highly efficient UV LEDs. We demonstrate that polarization-induced 3D charge is beneficial in reducing tunneling barriers especially for high composition AlGaN tunnel junctions. The design of graded tunnel junction structures could lead to low tunneling resistance below 10 -3 Ω cm 2 and low voltage consumption below 1 V (at 1 kA/cm 2 ) for high composition AlGaN tunnel junctions. Experimental demonstration of 292 nm emission was achieved through non-equilibrium hole injection into wide bandgap materials with bandgap energy larger than 4.7 eV, and detailed modeling of tunnel junctions shows that they can be engineered to have low resistance, and can enable efficient emitters in the UV-C wavelength range.a) Authors to whom correspondence should be addressed. Electronic mail: zhang.3789@osu.edu, rajan@ece.osu.edu 2The large range of direct bandgaps in the III-Nitride system makes these semiconductors uniquely suitable for achieving ultra violet emission over a wide wavelength range down to 210 nm. III-Nitride ultra-violet light emitting diodes (UV LEDs) have a large variety of applications including water purification and air disinfection, and they provide distinct advantages over traditional gas-based lamps. We propose an approach to realize highly efficient hole injection based on interband tunneling. In this approach, a transparent n-type AlGaN layer is connected to the p-AlGaN layer using an interband tunnel junction ( Fig. 1(b)). Non-equilibrium tunneling injection of holes overcomes limits imposed by thermal ionization of deep acceptors. 9,10 At the same time, it leads to efficient light extraction since it eliminates absorbing p-type top contact layers. 11Making efficient interband p-n tunnel junctions is challenging for ultra-wide bandgap AlGaN materials due to the large band gap, wide depletion barrier, and doping limitations. In this work, we show that nanoscale heterostructure and polarization engineering of tunnel junctions can enable highly efficient tunneling even for ultra-wide bandgap materials where ordinary dopant-based homojunctions would have very low tunneling current density. In this letter, we discuss the design of AlGaN tunnel junctions over the entire Al composition range. We then experimentally demonstrate highly efficient tunnel junctions for AlGaN with Al composition greater than 50%. was used for tunneling probability calculation, and tunneling current was calculated by considering all possible contributions by carriers with different energies. Bandtail states and bandgap narrowing effect due to heavy impurity doping are not included in the simulations, though they could lead to increase in the tunneling probability. ...

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confidence: 99%

Design and demonstration of ultra-wide bandgap AlGaN tunnel junctions

Zhang

Krishnamoorthy

Akyol

et al. 2016

Applied Physics Letters

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“…We have performed extensive studies of the nonpolar core–shell UV LED by comparing a uniaxial AlGaN nanowire UV LED which has vertical MQW heterostructures grown along a <0001> polar direction of n‐GaN nanowire. The detailed characterization of the uniaxial nanowire LED structures was described elsewhere . The core–shell UV‐LED device ( 318 nm wavelength) showed significantly smaller turn‐on voltage and reduced resistance compared to that of the uniaxial nanowire UV LED (322 nm wavelength), shown in Figure a.…”

Section: Resultsmentioning

confidence: 99%

Ultraviolet Light‐Emitting Diode Using Nonpolar AlGaN Core–Shell Nanowire Heterostructures

Kang

Lee

2018

Advanced Optical Materials

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To date, semiconductor light emitters have been developed to exceed 50% efficiency across the entire visible region. [6,7] However, the performance of AlGaNbased ultraviolet light-emitting diodes (LEDs) has been severely limited by the extremely inefficient strain-induced polarization fields and prohibitively large defect densities. Various approaches, including sputtered AlN nucleation layer, polarization doping, patterned sapphire substrate (PSS), AlGaN superlattices, and non-/ semipolars have been studied to improve the efficiency of LEDs in the ultraviolet region. [1,[8][9][10][11][12] Due to low magnesium (Mg)doping efficiency and large Mg activation energy, [13][14][15] AlGaN-based LEDs usually exhibit very high threshold voltages in the deep ultraviolet range. [13,16] Furthermore, the lattice mismatch between AlGaN materials and the substrate materials induces high dislocations and stacking faults with thermal stress in the Al-rich AlGaN epitaxial layers. [14] The AlGaN multiple quantum wells (MQWs) grown along a polar [0001] orientation suffer from inherent spontaneous and piezoelectric polarizations. The total polarization fields result in the spatial separation of the electron and hole wave functions and thus in restricting the radiative recombination efficiency, known as the quantum-confined Stark effect (QCSE). [17,18] As a result, because of the poor material quality and the polarization-induced electric field, it is still difficult to achieve internal quantum efficiency (IQE) in AlGaN epitaxial structures. This poor internal quantum efficiency eventually leads to extremely low output power of AlGaN-based LEDs operating in the UVA-C bands.Such critical issues can be potentially addressed by employing 1D nanowire structures and nonpolar core-shell heterostructures. [1,12] GaN-based nanowire structures have been intensively studied in the past decade. [19][20][21] Recent reports have shown that such nanowires can drastically reduce the dislocation densities due to efficient surface strain relaxation, and also can significantly enhance the p-type current conduction due to reduced Mg-dopant formation energy in p-Al(Ga)N structures. [22,23] With the use of nonpolar structures grown along m-plane direction in GaN structure, the improved light output power and electrical performance have been demonstrated in InGaN-based quantum well LEDs with the absence of polarization. [12,24,25] Therefore, it is expected that the incorporation of the nonpolar core-shell and the nanowire structures can significantly improve the internal quantum efficiency, p-contact Highly efficient nonpolar AlGaN nanowire ultraviolet light-emitting diode is developed, wherein core-shell AlGaN multiple quantum well layers are incorporated in the nonpolar active regions. It is confirmed that the core-shell light-emitting diode (LED) heterostructures are uniformly grown on the nonpolar surfaces of hexagonal GaN nanowires by metalorganic chemical vapor deposition (MOCVD) technique. At room temperature, the nearly defect-free core-shell AlGaN...

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“…Unlike DC‐HV LED, AC‐HV LED can directly work under AC without converter, thus reducing the cost of LED lighting systems, and avoiding more than 10% energy loss due to poor AC‐DC conversion efficiency. Wheatstone Bridge (WB) circuit is usually adopted in the AC‐HV LEDs to improve the device efficiency by increasing the radiation area in each bias direction . However, there is few works focusing on the direct comparison between DC‐HV LED and AC‐HV LED.…”

Section: Introductionmentioning

confidence: 99%

A Comparative Study of GaN‐Based Direct Current and Alternating Current High Voltage Light‐Emitting Diodes

Zhou

Gao

Zheng

et al. 2018

Physica Status Solidi (a)

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In this work, one type of direct current high voltage light‐emitting diode (DC‐HV LED) and six types of alternating current high voltage LEDs (AC‐HV LEDs) are demonstrated. Comparative current‐voltage (I–V) and light output power (LOP)‐current (L‐I) characteristics are performed between 24 V DC‐HV LED and 24 V AC‐HV LEDs with eight working cells. The AC‐HV LED has relatively larger wall‐plug efficiency (WPE) than DC‐HV LED over a current density range from 0 to 152 A cm−2. The effect of the layouts on the optical and electrical properties of AC‐HV LEDs is further investigated. Owing to larger heat dissipation area and fewer number of chips, our combined numerical and experimental results demonstrate that the AC‐HV LED I has a more favorable current spreading uniformity compared to other AC‐HV LEDs. In addition, it is found that the LOP of AC‐HV LEDs is dependent on both the number of working cells and the ratio of radiation area to total chip area. Larger ratio of light emission area to total chip area can be obtained by decreasing the area of rectifier cells. Therefore, in order to achieve a much higher LOP, AC‐HV LEDs have to be designed with smaller area of rectifier cells and with more working cells simultaneously.

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Alternating-Current InGaN/GaN Tunnel Junction Nanowire White-Light Emitting Diodes

Cited by 90 publications

References 51 publications

Design and demonstration of ultra-wide bandgap AlGaN tunnel junctions

Design and demonstration of ultra-wide bandgap AlGaN tunnel junctions

Ultraviolet Light‐Emitting Diode Using Nonpolar AlGaN Core–Shell Nanowire Heterostructures

A Comparative Study of GaN‐Based Direct Current and Alternating Current High Voltage Light‐Emitting Diodes

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