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A. V. Pomogaeva and A. Y. Timoshkin
by changing the substituents at the ends of the oligomer. A combined effect of
all considered factors, substituent groups variations, rod’s elongation, and the way
of ends’ termination, can help to vary energy gap of the [HGaNH] 3n rod-shaped
oligomer within the range 1–7 eV. Potential applications and further directions are
also discussed.
Keywords 13–15 compounds · Ga-N · Oligomers · Reaction mechanisms ·
DFT · Electronic properties
6.1 Introduction
In past decades, chemistry of oligomeric group 13–15 compounds has grown
dramatically due to their importance as precursors for semiconductor materials.
Group 13–15 binary compounds are prospective materials for microelectronics,
solar cell elements, light-emitting diodes, UV photodetectors, high electron mobility
transistors, and ceramic materials [1–3]. Among 13–15 binary compounds, the
gallium nitride stands out due to its unique properties and applications [4–6].
The simplest architectures of interest here are one-dimensional (1D) nanorods or
whiskers. One-dimensional nanopatterning of Ga-N surface results in significant
enhancement (by 40–60%) of the light output of Ga-N-based LEDs [7]. Production
of one-dimensional 13–15 architectures is an important task. Oligomer and 1D
polymer compounds are excellent precursors for the 13–15 materials. In 1990
only several 13–15 oligomer compounds have been experimentally known, mostly
amido- and iminoalanes [8]. Since then, the rapid developments in oligomer 13–15
chemistry have been the topic of numerous books and reviews [9–22].
Among the many possible structures of 13–15 oligomers, the needle-shaped or
rod-like compounds attracted special attention. These compounds can be considered
as a product of subsequent oligomerization of [RMYR’] 3 trimeric rings, which
can be either saturated with R,R’ substituents or capped by MR and YR’ groups,
resulting in open and closed oligomers, respectively (M = Al, Ga, In; Y = N, P,
As; R,R’ = H, halogens, or organic substituents). Their structures are schematically
shown in Fig. 6.1 on the example of [MeGaNH] 3n+1 .
It was computationally predicted that with the increase of the oligomerization
degree, these compounds become more stable than fullerene-like clusters for all
13–15 pairs [23, 24].
The key oligomerization degrees of closed [RMYR’] m oligomers are 4, 7, 10,
13, 16, etc., and they can be written as [RMYR’] 3n+1 , where n – number of trimeric
[RMYR’] 3 rings. The drum-type hexamer [RMYR’] 6 is a product of dimerization
of two trimeric [RMYR’] 3 rings.
Formation of oligomeric compounds in the gas phase at high temperatures
was proposed on the basis of the computational study of AlCl 3 -NH 3 system in
1997 [25] based on experimental observations of 13–15 nanoparticle formation in
CVD processes [26–30]. Experimental in situ mass spectrometry (MS) monitoring
A. V. Pomogaeva and A. Y. Timoshkin
by changing the substituents at the ends of the oligomer. A combined effect of
all considered factors, substituent groups variations, rod’s elongation, and the way
of ends’ termination, can help to vary energy gap of the [HGaNH] 3n rod-shaped
oligomer within the range 1–7 eV. Potential applications and further directions are
also discussed.
Keywords 13–15 compounds · Ga-N · Oligomers · Reaction mechanisms ·
DFT · Electronic properties
6.1 Introduction
In past decades, chemistry of oligomeric group 13–15 compounds has grown
dramatically due to their importance as precursors for semiconductor materials.
Group 13–15 binary compounds are prospective materials for microelectronics,
solar cell elements, light-emitting diodes, UV photodetectors, high electron mobility
transistors, and ceramic materials [1–3]. Among 13–15 binary compounds, the
gallium nitride stands out due to its unique properties and applications [4–6].
The simplest architectures of interest here are one-dimensional (1D) nanorods or
whiskers. One-dimensional nanopatterning of Ga-N surface results in significant
enhancement (by 40–60%) of the light output of Ga-N-based LEDs [7]. Production
of one-dimensional 13–15 architectures is an important task. Oligomer and 1D
polymer compounds are excellent precursors for the 13–15 materials. In 1990
only several 13–15 oligomer compounds have been experimentally known, mostly
amido- and iminoalanes [8]. Since then, the rapid developments in oligomer 13–15
chemistry have been the topic of numerous books and reviews [9–22].
Among the many possible structures of 13–15 oligomers, the needle-shaped or
rod-like compounds attracted special attention. These compounds can be considered
as a product of subsequent oligomerization of [RMYR’] 3 trimeric rings, which
can be either saturated with R,R’ substituents or capped by MR and YR’ groups,
resulting in open and closed oligomers, respectively (M = Al, Ga, In; Y = N, P,
As; R,R’ = H, halogens, or organic substituents). Their structures are schematically
shown in Fig. 6.1 on the example of [MeGaNH] 3n+1 .
It was computationally predicted that with the increase of the oligomerization
degree, these compounds become more stable than fullerene-like clusters for all
13–15 pairs [23, 24].
The key oligomerization degrees of closed [RMYR’] m oligomers are 4, 7, 10,
13, 16, etc., and they can be written as [RMYR’] 3n+1 , where n – number of trimeric
[RMYR’] 3 rings. The drum-type hexamer [RMYR’] 6 is a product of dimerization
of two trimeric [RMYR’] 3 rings.
Formation of oligomeric compounds in the gas phase at high temperatures
was proposed on the basis of the computational study of AlCl 3 -NH 3 system in
1997 [25] based on experimental observations of 13–15 nanoparticle formation in
CVD processes [26–30]. Experimental in situ mass spectrometry (MS) monitoring