Exploring the novel application to the quantum optics, the periodic crystallographic-polarity-inverted GaN waveguides were fabricated. In addition to the successful periodic reversal of the crystallographic orientations, periodic grating structures were formed on the surface due to the slight difference in the growth rates for different polarities, which gives the occurrence of the well-known photonic band structures. In this work, basic optical properties were investigated utilizing the variable-angle optical reflectance measurements on these waveguides with one-dimensional periodic grating structures, in order to obtain their photonic band structures. In addition to the optical interference fringes, clear reflectance dips originated from the resonance between the incident light and allowed waveguide modes appeared, aside from a weak resonant feature due to the coupling of the diffracted light to the evanescent mode on the grating surface, known as Wood's anomalies. Taking into account the refractive index dispersions and the zone-folding effects invoked by the grating, the origins of all the resonant features are successfully elucidated. Especially in case of resonant coupling to the waveguide modes, the corresponding orders of both the grating diffractions and the guided modes are assigned. Based on these assignments, the possible configurations of the wavelength conversions are discussed.
To promote the research on the growth of high-quality InN films attractive to the application for both optical and
electronic devices, the pressurized-reactor metalorganic-vapor-phase epitaxy (PR-MOVPE) system which can overcome
the high equilibrium-vapor-pressure of nitrogen between solid and vapor phases is originally developed. In addition to
this system, the N-polar growth technique developed in the growth of GaN is introduced. As a result, the dense InN films
with atomic steps are successfully grown. From the struggle of the research on high quality InN, the subject of the phase
purity is also arisen. The pole figure measurements make the growth condition for a pure InN with a wurtzite structure.
The phase purity is almost determined by the growth temperature. These results will pave the way to high-quality InN.
Nitride-semiconductor light-emitting-devices such as blue, green, and white LEDs, and 400nm-wavlength LDs have
been commercially available since 1993. The active layers in all these devices consist of InGaN, which composition is
designed for the wavelength of the emitted light. In this paper, the current status of MOVPE growth in GaN to InN,
including InGaN is reviewed. The GaN growth mechanism of two-step growth on a sapphire substrate, polarity-
controlled GaN growth, and the possibility in In-rich InGaN growth are described. The InN research as an ultimate
material of InGaN is also introduced. The future perspective of InN in device application is also mentioned.
In the application of nitride semiconductors for electronic and optical devices, spontaneous and piezoelectric
polarizations have been discussed recently. On the contrary, in light emitting devices, polarization is expected to be
absent. To suppress the polarization effect, GaN growth on A-plane and R-plane sapphire substrates has been attempted.
A-plane sapphire has crystallographical symmetry different from GaN. R-plane sapphire has large lattice-mismatch
from GaN. In this paper, GaN grown on an M-plane sapphire substrate which has been focused in 1990 is reviewed.
M-plane sapphire has a lattice-mismatched to GaN by less than 3%. Single-phase GaN was grown on sapphire tilted 15
degrees from an M-plane and its inclination of c-axis to the nominal axis of a substrate was by 32 degree. This number
is much attractive to suppress the polarization effect in light emitting devices.
This paper also describes N-polar GaN grown by MOVPE. Differently from the reported data about N-polar GaN
this N-polar GaN with a surface as smooth as Ga-polar one was obtained and the density of threading dislocations was in
order of 10<sup>18</sup>/cm<sup>2</sup>. p-type doping was also possible. This N-polar is very suitable for the growth of InN, which has the
high equilibrium-vapor-pressure of nitrogen, because N polarity has the advantage in the capture of nitrogen. The
growth and the properties of N-polar InN on N-polar GaN templates are reviewed. Finally, the perspectives of InN in
device applications are introduced.
Nitride-semiconductor technologies for blue lasers are reviewed. Nitride semiconductors from GaN to InN are covered with respect to MOVPE growth and characteristics. For GaN, two-step growth significantly improves crystalline characteristics, such as the concentration of residual carriers, mobility, and surface morphology. For InGaN, a key material for the emitting layer of blue lasers, the use of nitrogen as the carrier and bubbling gases for metalorganic sources enhances indium incorporation, and composition control has been achieved. The phase separation of InGaAlN system has been semiempirically predicted using the strictly regular solution model. As substrates for the epitaxial growth, a several materials are discussed along with the affect of the substrate polarity on
the characteristics of epitaxially grown GaN. P- and n-type doping are also briefly examined. Looking at future prospects for blue lasers, the effect of polarization in device structures and the bulk-crystal growth for substrates are described.
Conference Committee Involvement (2)
Optomechatronic Micro/Nano Devices and Components II
4 October 2006 | Boston, Massachusetts, United States