Tunneling-based carrier regeneration in cascaded GaN light emitting diodes to overcome efficiency droop

Akyol, Fatih; Krishnamoorthy, Sriram; Rajan, Siddharth

doi:10.1063/1.4819737

Cited by 76 publications

(71 citation statements)

References 26 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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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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“…Tunnel junctions also provides a pathway to circumvent efficiency droop in LEDs using a cascaded LED design run at low current density. 3 However, in order to incorporate TJ in commercial devices, low tunneling resistance is a prerequisite. Recently, tunnel junction device designs exploiting polarization in nitrides and embedded rare earth nitride nanoislands resulted in low resistance GaN tunnel junctions with resistivity as low as 10 -4 Ωcm 2 .…”

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InGaN/GaN tunnel junctions for hole injection in GaN light emitting diodes

Krishnamoorthy

Akyol

Rajan

2014

Applied Physics Letters

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“…However, using polarization engineering and mid-gap states assisted tunneling, highly efficient tunnel junctions (resistivity ~ 0.1 mOhm-cm 2 ), with orders of magnitude lower resistance has been demonstrated. 11,12,19 …”

Section: Mid Gap States Assisted Tunnelingmentioning

confidence: 98%

“…9,10 Cascading multiple active regions using tunnel junction interconnects provides a possible way to circumvent droop by operating the cascaded structure at low current density where the efficiency of individual emitter active regions is maximum. 11 For such a cascaded structure to operate efficiently, low resistance tunnel junctions is a prerequisite.…”

Section: Introductionmentioning

confidence: 99%

III-nitride tunnel junctions for efficient solid state lighting

2014

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We discuss the design and demonstration ultra-low resistance III-nitride tunnel junctions, and how tunnel junctions could solve the long-standing problem of efficiency droop in solid state lighting. We have used nanoscale band engineering based on polarization and mid-gap states to reduce tunneling resistance by four orders of magnitude. We will discuss experimental demonstration of highly efficient tunnel junctions (resistivity ~ 0.1 mOhm-cm 2 ) in PN junctions, p-contact free LEDs, and multiple junction structures. Finally we will show how tunneling based carrier regeneration in multiple active region cascade LEDs could help to enable low current, high voltage operation to overcome the efficiency droop problem.

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Tunneling-based carrier regeneration in cascaded GaN light emitting diodes to overcome efficiency droop

Cited by 76 publications

References 26 publications

Design and demonstration of ultra-wide bandgap AlGaN tunnel junctions

Design and demonstration of ultra-wide bandgap AlGaN tunnel junctions

InGaN/GaN tunnel junctions for hole injection in GaN light emitting diodes

III-nitride tunnel junctions for efficient solid state lighting

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