Free carrier mobility in AlGaN/GaN quantum wells

Farvacque, J. L.; Bougrioua, Z.; Carosella, Francesca; Moerman, Ingrid

doi:10.1088/0953-8984/14/48/384

Cited by 5 publications

(6 citation statements)

References 19 publications

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“…For even higher AlGaN thickness (54 nm, not shown) no 2DEG could be detected. The strong mobility decay for high carrier density has recently been theoretically attributed to an increase of "interface-roughness-like" scattering mechanism [7]. The question that arises then is what is this "interface-like" scattering potential?…”

Section: Relaxation In Algan Thin Layersmentioning

confidence: 99%

Engineering of an insulating buffer and use of AlN interlayers: two optimisations for AlGaN–GaN HEMT-like structures

Bougrioua

Moerman

Nistor

et al. 2003

phys. stat. sol. (a)

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The semi-insulating character of GaN epitaxial layers can be achieved by the control of the early stages of growth on the substrate. Adding two low temperature (LT) AlN interlayers is a technique enough powerful to reduce threading dislocation densities by up to one order of magnitude. A compressive strain as high as 2.8 × 10 −3 is induced in the uppermost GaN epilayer. The global structure is kept semi-insulating so that it is a perfect template for undoped AlGaN − GaN HEMTs (High Electron Mobility Transistors). HEMTs with interlayers present better two dimensional electron gas (2DEG) properties: up to 20% higher carrier density (n S ) and 40% higher mobility. Typically n S is as high as 1.7 × 10 13 cm −2 for a record mobility of 1200 cm 2 /Vs. The improvement of the mobility can be correlated to the reduction of nano-scale V-shaped defects in the AlGaN (less morphological-relaxation). The improvement of n S could be explained by the higher piezo-doping resulting from GaN extra-compression and AlGaN weaker relaxation. As a consequence, the DC transistors characteristics are improved: in 2 µm gate transistors, the maximum current and transconductance are increased by up to 80% and 20%, respectively, and could be extrapolated to values as high as 1500 mA/mm and 250 mS/mm for 0.2 µm gate devices.

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Section: Relaxation In Algan Thin Layersmentioning

confidence: 99%

Engineering of an insulating buffer and use of AlN interlayers: two optimisations for AlGaN–GaN HEMT-like structures

Bougrioua

Moerman

Nistor

et al. 2003

phys. stat. sol. (a)

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“…In contrast, the low-temperature mobility is rather controlled by electron scattering related to the background ionized impurities, charged dislocation cores, small-scale interface roughness, and alloy disorder in the AlGaN cap layers [1][2][3][4][5]. Two former mechanisms dominate at the 2DEG concentration n less than ∼ 10 12 cm −2 .…”

Section: Introductionmentioning

confidence: 99%

“…1 Introduction Scattering by optical phonons is the principal mechanism limiting the room-temperature mobility of two-dimensional electron gas (2DEG) in AlGaN/GaN high-electron mobility transistor (HEMT) heterostructures (see, for instance, [1]). In contrast, the low-temperature mobility is rather controlled by electron scattering related to the background ionized impurities, charged dislocation cores, small-scale interface roughness, and alloy disorder in the AlGaN cap layers [1][2][3][4][5]. Two former mechanisms dominate at the 2DEG concentration n less than ∼ 10 12 cm −2 .…”

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confidence: 99%

Assessment of the pendeo‐epitaxy effect on 2DEG mobility in III‐nitride HEMT heterostructures

Bulashevich¹,

Karpov²,

Makarov³

et al. 2008

Phys. Status Solidi (c)

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We have analyzed theoretically the electron scattering related to the interface roughness produced by threading dislocations in the channel of an AlGaN/GaN HEMT heterostructure. On the basis of the analysis, we predict the use of the pendeo‐epitaxy for growing the transistor structure to improve the low‐temperature and roomtemperature mobility of two‐dimensional electrons by ∼80% and ∼28%, respectively. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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“…AlGaN/GaN heterostructures possess attractive electronic and mechanical properties, which make them interesting for being implemented in the production of devices capable of high performance and able to work in hostile environments. One of their most unusual features is the presence, at the AlGaN/GaN interface, of a two-dimensional electron gas (2DEG) with carrier densities n s as high as 10 13 cm −2 , even in nominally 1 Present address: Institut d'Electronique Fondamentale, Université Paris Sud, Bât. 220-Centre scientifique d'Orsay, 91405 Orsay, France.…”

Section: Introductionmentioning

confidence: 99%

“…A lot of experimental and theoretical work is devoted to the understanding of the electronic properties of this quantum well, but also to the characterization of the interface defects and to the understanding of the way they may interact with the electrons limiting their 2D mobility. In some of the authors' previous studies about transport in AlGaN/GaN quantum wells [1,2], the effect of the interface defects (like misfit dislocations, surface cracks, alloy reordering etc), originated by the relaxation of the strain energy accumulated in the AlGaN top layer, was referred to as 'interface electrical roughness', because of the non-uniform charge distribution induced by such defects at the interface. The results showed that this scattering mechanism contributes to the room temperature mobility drop at high electron concentration.…”

Section: Introductionmentioning

confidence: 99%

Effect of threading dislocations on carrier mobility in AlGaN/GaN quantum wells

Carosella¹,

Farvacque²

2008

J. Phys.: Condens. Matter

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The various scattering mechanisms induced by dislocations have been reviewed and adapted to the case of threading dislocations in AlGaN/GaN quantum wells. These scattering mechanisms can be classified into two categories, the first one issuing straightforwardly from the dislocation strain field, the other one being due to the Coulomb potential created by electrons trapped on the energy states that dislocations may create in the GaN band gap. For the first category of mechanisms (strain field effects), we indicate that edge dislocations can only be connected with the so-called deformation potential, the piezoelectric coupling being ruled out because of the particular geometry of the threading dislocation strain fields. We show that the dislocation deformation potential can only be responsible for a very weak, even negligible, effect on the carrier mobility. Then, after a survey of the various results found in the literature concerning the possible existence of dislocation energy states we conclude that dislocations are responsible for the existence of shallow acceptor states below the conduction band and propose a model for describing the potential associated with such states when filled by electrons. More particularly, we show that the linear dislocation charge density resulting from the trapped carriers at dislocation states can not be uniform, as it is systematically assumed in the literature, and we propose a description of this linear charge density as a function of the dislocation energy state position and of the various features characterizing the quantum well. Using the scattering potential induced by such a spatially-dependent dislocation charge density together with the usual scattering mechanisms allows us to give an estimation of their effect on the free carriers’ mobility. We particularly show that at low carrier density (∼1012 cm−2) the mobility is mainly determined by the combination of dislocation scattering mechanisms and intrinsic scattering mechanisms. Finally we suggest that our model could be employed for determining the position of the dislocation energy level in the gap.

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Free carrier mobility in AlGaN/GaN quantum wells

Abstract: Experimental results show that the free carrier mobility in AlGaN/GaN quantum wells strongly decreases with the carrier density. Using the dynamical theory, we show that this behaviour can be explained by a combination of phonon, carrier-carrier and interface defect scattering mechanisms.

Cited by 5 publications

References 19 publications

Engineering of an insulating buffer and use of AlN interlayers: two optimisations for AlGaN–GaN HEMT-like structures

Engineering of an insulating buffer and use of AlN interlayers: two optimisations for AlGaN–GaN HEMT-like structures

Assessment of the pendeo‐epitaxy effect on 2DEG mobility in III‐nitride HEMT heterostructures

Effect of threading dislocations on carrier mobility in AlGaN/GaN quantum wells

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