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1

Bands, Bonds, and Polarizations in Nitrides - from Electronic Orbitals to Electronic Devices

100%

Majewski J., Zandler G., Vogl P.

Acta Physica Polonica A

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2001

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vol. 100

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issue 2

249-260

EN

A key property of the nitrides is the fact that they possess large spontaneous and piezoelectric polarization fields that allow a significant tailoring of the carrier dynamics and optical properties of nitride devices. In this paper, based on first-principles calculations of structural and electronic properties of bulk nitrides and their heterostructure, we investigate the potential of this novel material class for modern device applications by performing self-consistent Monte Carlo simulations. Our studies reveal that the nitride based electronic devices have characteristics that predispose them for high power and high frequency applications. We demonstrate also that transistor characteristics are favorably influenced by the internal polarization induced electric fields.

2

Effect of Nonlinear Elasticity on Interband and Intersubband Transition Energies in GaN/AlN Superlattices

80%

Łepkowski S.

Acta Physica Polonica A

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2007

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vol. 112

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issue 2

315-319

EN

We present a theoretical study of the effect of nonlinear elasticity on interband and intersubband transition energies in wurtzite GaN/AlN superlattices. The effect of nonlinear elasticity is considered by taking into account the changes of elastic constants caused by the intrinsic hydrostatic pressure, originating from lattice misfit between constituents of the superlattice. We show that the influence of the effect of the nonlinear elasticity on the interband and intersubband transition energies in the GaN/AlN superlattices depends crucially on the strain state of structures, in particular on the in-plane lattice constant of the buffer or the substrate. For the superlattices strained to AlGaN buffers with small aluminum concentrations, the effect of nonlinear elasticity increases significantly the interband transition energy and decreases the intersubband transition energy. For the superlattices strained to AlGaN buffers with large aluminum concentrations, the effect of nonlinear elasticity leads to a decrease in the interband transition energy and an increase in the intersubband transition energy.

3

Photo- and Electroreflectance Spectroscopy of Low-Dimensional III-Nitride Structures

80%

Drabińska A.

Acta Physica Polonica A

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2003

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vol. 104

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issue 2

149-164

EN

The review of electromodulation techniques such as photo- and electroreflectance spectroscopy is presented and illustrated using spectra of AlGaN/GaN heterostructures. By using these techniques it is possible to analyze the Franz-Keldysh oscillations to obtain the value of electric field near the surface or at interface. When additionally a constant voltage is applied to the structure, it is possible to obtain the charge distribution or the gradient of polarization present in the sample, which is of the origin of 2D electron gas at the AlGaN/GaN interface. The polarization is discussed assuming two contributions: spontaneous and piezoelectric polarization. Piezoelectric part of polarization can be obtained from X-ray diffraction, providing information about strain in the structure. Influence of light and voltage on 2D electron gas properties and depletion layer width is demonstrated using photocapacitance-voltage measurements. All results are discussed and compared with self-consistent calculations of potentials and electric fields in the structure.

4

Polarization Induced Effects in AlGaN/GaN Heterostructures

80%

Ambacher O.

Acta Physica Polonica A

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2000

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vol. 98

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issue 3

195-201

EN

Two-dimensional hole and electron gases in wurtzite GaN/Al_{x}Ga_{1-x}N/GaN heterostructures areinduced by strong polarization induced effects. The sheet carrier concentration and the confinement of the two-dimensional carrier gases located close to one of the AlGaN/GaN interfaces are sensitive to a high number of different physical properties such as polarity, alloy composition, strain, thickness, and doping. We have investigated the structural quality, the carrier concentration profiles, and electrical transport properties by a combination of high resolution X-ray diffraction, Hall effect, and C-V profiling measurements. The investigated heterostructures with N- and Ga-face polarity were grown by metalorganic vapor phase or plasma induced molecular beam epitaxy covering a broad range of alloy compositions and barrier thickness. By comparison of theoretical and experimental results we demonstrate that the formation of two-dimensional hole and electron gases in GaN/AlGaN/GaN heterostructures both rely on the difference of the polarization between the AlGaN and the GaN layer. In addition the role of polarity on the carrier accumulation at different interfaces in n- and p-doped heterostructures will be discussed in detail.

5

Modeling of Semiconductor Nanostructures with nextnano^3

61%

Birner S., Hackenbuchner S., Sabathil M., Zandler G., Majewski J., Andlauer T., Zibold T., Morschl R., Trellakis A., Vogl P.

Acta Physica Polonica A

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2006

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vol. 110

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issue 2

111-124

EN

nextnano^3 is a simulation tool that aims at providing global insight into the basic physical properties of realistic three-dimensional mesoscopic semiconductor structures. It focuses on quantum mechanical properties such as the global electronic structure, optical properties, and the effects of electric and magnetic fields for virtually any geometry and combination of semiconducting materials. For the calculation of the carrier dynamics a drift-diffusion model based on a quantum-mechanically calculated density is employed. In this paper we present an overview of the capabilities of nextnano^3 and discuss some of the main equations that are implemented into the code. As examples, we first discuss the strain tensor components and the piezoelectric effect associated with a compressively strained InAs layer for different growth directions, secondly, we calculate self-consistently the quantum mechanical electron density of a Double Gate MOSFET, then we compare the intersubband transitions in a multi-quantum well structure that have been obtained with a single-band effective mass approach and with an 8-band k·p model, and finally, we calculate the energy spectrum of a structure in a uniform magnetic field.

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5 Acta Physica Polonica A

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2 Majewski J.

2 Vogl P.

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1 Ambacher O.

1 Andlauer T.

1 Birner S.

1 Drabińska A.

1 Hackenbuchner S.

1 Morschl R.

1 Sabathil M.

1 Trellakis A.

1 Zibold T.

1 Łepkowski S.

Bands, Bonds, and Polarizations in Nitrides - from Electronic Orbitals to Electronic Devices

Effect of Nonlinear Elasticity on Interband and Intersubband Transition Energies in GaN/AlN Superlattices

Photo- and Electroreflectance Spectroscopy of Low-Dimensional III-Nitride Structures

Polarization Induced Effects in AlGaN/GaN Heterostructures

Modeling of Semiconductor Nanostructures with nextnano^3