Cubic group-III nitride-based nanostructures—basics and applications in optoelectronics

doi:10.1016/j.mejo.2008.07.036

Microelectronics Journal

Volume 40, Issue 2, February 2009, Pages 204-209

https://doi.org/10.1016/j.mejo.2008.07.036 Get rights and content

Abstract

Molecular beam epitaxy (MBE) of cubic group-III nitrides is a direct way to eliminate the polarization effects which inherently limits the performance of optoelectronic devices containing quantum well or quantum dot active regions. In this contribution the latest achievement in the MBE of phase-pure cubic GaN, AlN, InN and their alloys will be reviewed. A new reflected high-energy electron beam (RHEED) control technique enables to carefully adjust stoichiometry and to severely reduce the surface roughness, which is important for any hetero-interface. The structural, optical and electrical properties of cubic nitrides and AlGaN/GaN will be presented. We show that no polarization field exists in cubic nitrides and demonstrate 1.55 μm intersubband absorption in cubic AlN/GaN superlattices. Further the progress towards the development and fabrication of cubic hetero-junction field effect transistors (HFETs) is discussed.

Introduction

State-of-the-art group-III nitride-based electronic and optoelectronic devices based on nitride films are grown along the polar c-direction, which suffer from the existence of strong “built-in” piezoelectric and spontaneous polarization. This inherent polarization limits the performance of optoelectronic devices containing quantum well (QW) or quantum dot active regions. To get around this problem much attention has been focused on the growth of non- or semi-polar (Al, Ga, In)N in the last few years. However, the direct way to eliminate polarization effects will be to use non-polar (0 0 1)-oriented zinc-blend III nitride layers. With cubic epilayers, a direct transfer of the existing GaAs technology to cubic III nitrides will be possible and the fabrication of diverse electronics and optoelectronic devices will be facilitated. In this paper the latest achievement in the molecular beam epitaxy (MBE) of phase-pure cubic GaN, AlN, InN and their application in optoelectronic devices will be reviewed.

Section snippets

Experiment

Cubic group-III nitride samples were grown on 200 μm thick, free standing 3C-SiC (0 0 1) substrates by MBE [1], [2]. An Oxford Applied Research HD25 radio frequency plasma source was used to provide activated nitrogen atoms. Indium, aluminum and gallium were evaporated from Knudsen cells. Prior to growth, the 3C-SiC substrates were chemically etched by organic solvents and a buffered oxide etch (BOE) and annealed for 10 h at 500 °C. Cubic GaN layers were deposited at 720 °C directly on 3C-SiC

RHEED control

As an important step to improve the GaN surface morphology in a systematic way, it is essential to understand the surface structure and the underlying growth process on an atomic scale. In particular, the kinetic processes of adsorption and desorption on the surface are considered as key parameters that govern the surface morphology, incorporation kinetics and consecutively the overall material quality. In MBE of GaN, two dimensional surfaces are commonly achieved under Ga-rich conditions, with

Conclusion

Cubic group-III nitrides grown by MBE may form the basis for future non-polar optoelectronic and electronic devices, which are not restricted by the inherent polarization effects. A new RHEED control technique enables to carefully adjust stoichiometry and to severely reduce the surface roughness. The structural, optical and electrical properties of cubic nitrides and AlGaN/GaN are presented. We proved the absence of polarization field in cubic nitrides and demonstrated 1.55 μm intersubband

Acknowledgements

The author wants to thank K. Lischka, S. Potthast, J. Schörmann, E. Tschumak, T. Schupp at University of Paderborn, Prof. M.O. Manasreh and E. DeCuir, Jr. at Arkansas State University, J. Gerlach at IOM Leipzig. R. Goldhahn at University of Ilmenau and T. Veal at University of Warwick. My special regards are expressed to Dr. M. Abe and Dr. H. Nagasawa at HOYA Corporation, for the supply of excellent 3C-SiC substrates and the financial support by DFG.

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For the past decades, group III-V and II-VI semiconductors have been at the forefront of semiconductor advances. However, the ionic bonds and non-centrosymmetry of their crystal structure – wurtzite or zinc-blende – imply that these materials are prone to exhibit piezoelectric effects. While piezoelectricity can be desired in some semiconductor devices, it can be harmful to others. After a general overview of the structural, piezoelectric, and electronic properties of group III-V and II-VI semiconductor materials we present the effect of piezoelectricity on devices and discuss mitigation strategies in relation to piezoelectricity.
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III-nitrides based on the zincblende (zb) crystal structure can offer a potential solution to the ‘green gap’ problem, due to the absence of internal electric fields [1], which affect the commonly used c-plane wurtzite (wz) crystal structure and result in the quantum-confined Stark effect [2].
Cubic zincblende (zb-)GaN nucleation layers (NLs) grown by MOVPE on 3C-SiC/Si substrates were studied to determine their optimal thickness for subsequent zb-GaN epilayer growth. The layers were characterised by atomic force microscopy, X-ray diffraction and scanning transmission electron microscopy. The as-grown NLs, with nominal thicknesses varying from 3 nm to 44 nm, consist of small grains which are elongated in the [1 −1 0] direction, and cover the underlying SiC surface almost entirely. Thermal annealing of the NLs by heating in a H₂/NH₃ atmosphere to the elevated epilayer growth temperature reduces the substrate coverage of the films that are less than 22 nm thick, due to both material desorption and the ripening of islands. The compressive biaxial in-plane strain of the NLs reduces with increasing NL thickness to the value of relaxed GaN for a thickness of 44 nm. Both the as-grown and annealed NLs are crystalline and have high zincblende phase purity, but contain defects including misfit dislocations and stacking faults. The zb-GaN epilayers grown on the thinnest NLs show an enhanced fraction of the wurtzite phase, most likely formed by nucleation on the exposed substrate surface at elevated temperature, thus dictating the minimum NL thickness for phase-pure zb-GaN epilayer growth.
First-principles calculations of half-metallic ferromagnetism of AlC<inf>0.0625</inf>N<inf>0.9375</inf> and AlC<inf>0.125</inf>N<inf>0.875</inf>-zincblende
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Computational calculations based on density functional theory were used to study the structural, electronic, and magnetic properties of the AlC_0.0625N_0.9375 and AlC_0.125N_0.875 compounds in the cubic zincblende phase. The calculations were carried out by means of the pseudopotential method, employing the computational Quantum ESPRESSO package. The density of states showed that the compounds has a half-metallic character. The calculated total magnetic moments of AlC_0.0625N_0.9375 and AlC_0.125N_0.875 were 1.0 μ_β and 2.0 μ_β per cell, respectively, the mainly contribution of the total magnetic moment come from 2p-C orbital. The computational calculations predict a Curie temperature of 875 K, which is higher than room temperature. The results suggest that AlN zincblende doped with C is a promising candidate to be a good diluted magnetic semiconductor material.
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The molecular beam epitaxy (MBE) of cubic group III-nitrides is a direct way to eliminate polarization effects, which may limit the performance of optoelectronic devices containing quantum well or quantum dot (QD) active regions. In this paper, recent progress with the MBE of phase-pure cubic GaN, AlN, and their alloys is reviewed. Reflection high-energy electron diffraction has extensively been used to adjust stoichiometric growth conditions allowing severe reduction of the surface roughness of layers and optimization of the hetero-interfaces and structural quality of multilayer stacks. The absence of polarization fields in cubic nitride nanostructures has been demonstrated. We summarize the performance of device structures taking advantage of this property, like heterojunction field-effect transistors with both normally on and normally off characteristics, as well as devices for intersubband absorption in the spectral range between 1.55 μm and the terahertz region and single photon emission of cubic GaN QDs.
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Of the 10,000 + journal articles that have been written on GaN-based materials, less than 2% reported on the cubic material phase of GaN, and a yet fewer experimentally studied light-emitting structures of cubic phase (As et al., 2000; Brandt et al., 1998; Chichibu et al., 2001, 2003a; DeCuir et al., 2007; Goldys et al., 1999; Kohler et al., 2002; Li et al., 2005, 2007; Nakadaira and Tanaka, 1997; Radosavljevic et al., 2014; Tanaka and Nakadaira, 2000; Taniyasu et al., 2000; Wu et al., 1999; Yang et al., 1999). As such, there exists a need for a better approach for generating cubic phase GaN materials that could not only close the “green gap” but also open up cubic phase for applications ranging from polarization-free photonics (As, 2009) and room-temperature ferromagnetism (Chitta et al., 2004) to high-temperature spintronics (Bub et al., 2014), normally-off transistors (Abe et al., 2006; Ghosh et al., 2014; Granzner et al., 2011), and single-photon emitters (Kako et al., 2014). This chapter aims filling this knowledge gap in an effort to break these six fundamental barriers limiting SSL.
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Cubic group-III nitride-based nanostructures—basics and applications in optoelectronics

Abstract

Introduction

Section snippets

Experiment

RHEED control

Conclusion

Acknowledgements

Mater. Sci. Forum

Phys. Rev. B

Appl. Phys. Lett.

Phys. Rev. B

Phys. Rev. B

Appl. Phys. Lett.

Phys. Rev. Lett.

Phys. Rev. B

J. Appl. Phys.

Appl. Phys. Lett.

Phys. Rev. Lett.

J. Appl. Phys.

Semicond. Sci. Technol.