GaN Nanowall Network: Laser Assisted Molecular Beam Epitaxy Growth and Properties
Low dimensional structures such as two-dimensional (2D) nanowalls, 1D nanorods or nanowires and 0-D quantum dots of semiconductors exhibit different mechanical, electrical and optical properties compared to their bulk counterpart. Despite the promising pr
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GaN Nanowall Network: Laser Assisted Molecular Beam Epitaxy Growth and Properties M. Senthil Kumar and Sunil S. Kushvaha
9.1
Introduction
Group III-nitride materials, such as InN, GaN, AlN and their alloys, are the well-established semiconductors for the fabrication of high efficiency blue/green light emitting diodes (LEDs) and laser diodes (LDs) [1–3]. III-nitride LEDs are also the backbone for the current solid state lighting technology [4, 5]. Because of small size, light weight, high efficiency and long life time, nitride LEDs find a wide range of applications in the field of room lighting, displays, traffic lights, automobiles, etc. The excellent physical properties of group III-nitrides such as direct bandgap with a large tunability, high carrier mobility, high electron saturation velocity, high breakdown field, good mechanical and thermal conductivity, radiation hardness etc. are behind this success and make III-nitrides second most important semiconductors after silicon. Some of the important properties of wurtzite III-nitride semiconductors are listed in Table 9.1 [6–8]. Currently, III-nitrides are being explored for their potential applications in the field of short wavelength optoelectronics, high power electronics, photovoltaics and spintronics as well. Efficient AlGaN based ultraviolet (UV) LEDs are soon expected to replace UV lamps as they are free from ozone generation and mercury. On the other hand, the in-built spontaneous and piezoelectric polarization fields of GaN have led the way to realize AlGaN/GaN heterostructure based high electron mobility transistors (HEMTs) for micro- and millimeter-wave power electronics [9, 10]. Due to their robust nature, GaN based HEMTs can be used in extreme environmental applications such as space, satellite, and military systems. M. Senthil Kumar (&) S.S. Kushvaha (&) CSIR-National Physical Laboratory, Dr. K.S. Krishnan Road, New Delhi 110012, India e-mail: [email protected] S.S. Kushvaha e-mail: [email protected] © Springer Nature Singapore Pte Ltd. 2017 Z.H. Khan (ed.), Recent Trends in Nanomaterials, Advanced Structured Materials 83, DOI 10.1007/978-981-10-3842-6_9
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Table 9.1 Important physical properties of wurtzite III-nitride semiconductors [6–8] Property
InN
GaN
AlN
Lattice constants
3.533 5.693 0.64 9 3.8 10−6 2.9 10−6 *0.8 10.5 6.81 2146 630 1.98
3.189 5.185 3.43 34 5.6 10−6 3.2 10−6 1.3 8.9 6.15 2791 850 2.20
3.112 4.982 6.14 60 4.2 10−6 5.3 10−6 2.85 8.5 3.23 3487 1040 2.88
a (Å) c (Å) Band gap energy Eg (eV) at 300 K Exciton binding energy (meV) Thermal expansion Da/a (K−1) Dc/c (K−1) Thermal conductivity (W cm−1 K−1) Dielectric constant (er) Density q (g cm−3) Melting point (K) Decomposition temperature (K) Binding energy (eV)
III-nitride device structures are generally grown on foreign substrates due to the lack of large-sized bulk GaN substrates, using metal organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE) techniques. The MOCVD and MBE techniques empl
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