Evidence for nonlinear macroscopic polarization in III–V nitride alloy heterostructures

Fiorentini, Vincenzo; Bernardini, Fabio; Ambacher, O.

doi:10.1063/1.1448668

Cited by 776 publications

(356 citation statements)

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“…As implied by its definition, d↔ is relevant to electroacustic applications [3], and to the determination of polarization and electrostatic fields induced by applied stress or strain in devices or epitaxial nanostructures [4].The piezoelectric tensor e ↔ [1,5] connecting polarization and strain ǫ i viais related to the d ↔ tensor of interest here bywhere the C ij are the elastic stiffness constants at constant electric field. It is thus possible to compute d ↔ from the knowledge of elastic constants and e-piezoconstants (using e.g.…”

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confidence: 99%

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First-principles calculation of the piezoelectric tensor d⇊ of III–V nitrides

Bernardini¹,

Fiorentini²

2002

Applied Physics Letters

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135

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We report direct first-principles density-functional calculations of the piezoelectric tensor d The piezoelectric tensor d ↔ of a polar material relates to linear order the induced polarization P to the applied stress viaIt is an especially relevant quantity in the field of III-V nitride compounds, whose piezoelectric and polarization properties are prominent [1] and unusual [2]. As implied by its definition, d↔ is relevant to electroacustic applications [3], and to the determination of polarization and electrostatic fields induced by applied stress or strain in devices or epitaxial nanostructures [4].The piezoelectric tensor e ↔ [1,5] connecting polarization and strain ǫ i viais related to the d ↔ tensor of interest here bywhere the C ij are the elastic stiffness constants at constant electric field. It is thus possible to compute d ↔ from the knowledge of elastic constants and e-piezoconstants (using e.g. the theoretical estimates of Refs.[5] and [6], see also below). On the other hand, experiments [7][8][9][10][11][12] directly access the d ij measuring the strain ǫ i caused by an applied field E via the converse piezoelectric effectThe d ij 's in Eqs. 1 and 4 are by definition identical [13], so that a direct comparison is possible, and especially interesting and useful. Here we compute directly the d ij constants in the III-V binary nitrides as derivatives of the polarization with respect to stress, calculating the Berryphase polarization of a primitive cell explicitly subject to a given external stress. This approach enables us to directly compare the calculated values with experiment, and with indirect theoretical predictions using Eq. 3, and separately calculated C ↔ and e ↔ tensors. The binary III-V nitrides AlN, GaN, and InN crystallize in the wurtzite structure, and they possess three independent components of the piezoelectric tensor, namely d 33 , d 31 (=d 32 ), and d 15 (=d 24 ). To compute these constants we run a damped Parrinello-Rahman-like dynamics [14,15] for each of the compounds considered, with the constraint that the system be subject to a given non-zero stress. The external stress is applied to the zero-stress equilibrium structure, which is identical to that reported in Ref. [5]. As a compromise between the contrasting needs for sufficiently large stresses to obtain polarizations outside the numerical noise, and for sufficiently small stresses to avoid large deformations and non-linearity, we separately apply stress components σ 1 = σ 2 = ±50 Kbar in the basal plane, and σ 3 = ±50 Kbar along the singular axis, to determine d 31 and d 33 ; for d 15 we apply a shear stress σ 5 = ±50 kBar. In the case of InN, these stresses and the ensuing deformations may lead to metallization because of the very small calculated DFT band gap. This must be avoided because macroscopic polarization cannot be defined or computed in metallic systems. We found that the maximum applied stress had to be reduced to 5 Kbar for InN (incidentally, this does not causes numerical noise problems in the polarization cal...

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mentioning

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“…↔ is relevant to electroacustic applications [3], and to the determination of polarization and electrostatic fields induced by applied stress or strain in devices or epitaxial nanostructures [4].…”

mentioning

confidence: 99%

First-principles calculation of the piezoelectric tensor d⇊ of III–V nitrides

Bernardini¹,

Fiorentini²

2002

Applied Physics Letters

Self Cite

135

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“…[26,27] The polarization charges are based on ref. [28], but they have been scaled by 0.5 to phenomenologically account for the screening of the polarization charges by, e.g., surface states and indium fluctuations. data.…”

Section: Theorymentioning

confidence: 99%

On the Monte Carlo Description of Hot Carrier Effects and Device Characteristics of III‐N LEDs

Kivisaari

Sadi

et al. 2017

Adv Elect Materials

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of LED operation remain poorly understood, presenting an obvious bottleneck for further LED development and optimization. [5] For example, recent measurements have shown that III-N LEDs exhibit notable hot carrier distributions already close to the peak efficiency, [6][7][8][9] suggesting that hot carriers might have a more profound effect on the device characteristics than previously anticipated.To date, conventional LED simulations have mainly relied on the drift-diffusion (DD) model (see, e.g., refs. [10-13]), which cannot genuinely account for hot carriers and generally also produces larger turnon voltages for MQW LEDs than observed experimentally. [14] Many reasons have been suggested to explain this discrepancy, including charge transport through indium fluctuations, [15] V-shaped pits, [16] tunneling through traps [17] or hot carrier transport. [18] At present it is, however, unclear if the discrepancy is of a physical origin or if it arises simply because the very foundations of the widely adopted DD model make it incapable of predicting the most essential device-level characteristics of LEDs.The Monte Carlo (MC) method has been established as the standard tool to simulate hot-carrier effects in unipolar semiconductor devices such as transistors. Recently the MC method has also been expanded by Bertazzi et al. to simulate hot electron effects in GaN barriers of LEDs using full-band MC methods, [19] and ourselves, as we have recently developed a coupled Monte Carlo-drift-diffusion (MCDD) simulation method to investigate hot-electron effects in full III-N MQW LED structures. [20][21][22] More recently, we have also introduced a full MC model, [23] which can be used to carry out full MC simulations of both electrons and holes in a complete LED device. Nevertheless, the previous works have not yet provided a full analysis of the pertinent physics and differences between MC and DD. To provide more insight into the physics of MQW devices and to facilitate their further development, we now deploy our full MC simulator to answer the following questions:

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“…This is one of the AlGaN/GaN heterostructure properties and advantages over other heterojunctions. In this case there are two types of macroscopic polarizations [15]:…”

Section: Plasmon Frequency In 2deg Systemmentioning

confidence: 99%

“…It was found experimentally [15,16] that the nonlinear model is more accurate than linear ones which were considered in some research works.…”

Section: Plasmon Frequency In 2deg Systemmentioning

confidence: 99%

Charge density and plasmon modes in a triangular quantum well model for doped and undoped gated AlGaN/GaN HEMTs

Rabbaa¹,

Stiens²

2011

J. Phys. D: Appl. Phys.

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To cite this version:S Rabbaa, J Stiens. Charge density and plasmon modes in a triangular quantum well model for doped and undoped gated AlGaN/GaN HEMTs. Journal of Physics D: Applied Physics, IOP Publishing, 2011, 44 (32) Abstract. We have calculated the plasmon frequency of the two-dimensional electron gas (2DEG) in AlGaN/GaN high electron mobility transistors (HEMT). The impact of HEMT's parameters on the plasmon frequency and the sheet charge density of the 2DEG is discussed in detail. The charge density in the HEMT's channel is calculated by means of a triangular quantum well (TQW) model. It has been found that the AlGaN/GaN heterostructure induces plasmon oscillations in the THz range with larger frequencies compared to other semiconductor compounds. The sensitivity of the tunability of these frequencies is considerable, especially by using a variable applied gate voltage. We have derived optimal structure parameters for obtaining a maximum plasmon frequency for a given doping concentration. We will show that the accuracy of this optimized frequency value is dependent on the average position ∆d of charge density in the triangular shaped (quantum well) channel. The interaction between radiation and plasmons has many applications such as detectors, mixers and generators of THz waves.

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Evidence for nonlinear macroscopic polarization in III–V nitride alloy heterostructures

Cited by 776 publications

References 15 publications

First-principles calculation of the piezoelectric tensor d⇊ of III–V nitrides

First-principles calculation of the piezoelectric tensor d⇊ of III–V nitrides

On the Monte Carlo Description of Hot Carrier Effects and Device Characteristics of III‐N LEDs

Charge density and plasmon modes in a triangular quantum well model for doped and undoped gated AlGaN/GaN HEMTs

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