Materials Design Division

Physics of Electronic Materials

Prof. Takashi MATSUOKA
Lecturer Tomoyuki TANIKAWA
Assist. Prof. Takashi HANADA
Assist. Prof. Shigeyuki KUBOYA

Creation of Innovative Energy-Saving Devices by Development of Crystal Growth Technology
and Control of Physical Properties of Nitride Semiconductors

Our target is to develop new electronic materials which can open up novel device applications. The materials of our current interest are nitride semiconductors, InGaAlN mixed crystal system, which is well known as materials for blue lightemitting- diodes (LEDs). Taking advantages of our epitaxial growth reactors developed by ourselves and a series of device fabrication equipment, we are going toward the further contribution to the global societies in terms of the energy saving, by developing high-power electronic devices and high-efficiency light-emitting devices.

Since our first proposal of InGaAlN system for wide-spectral-range light-emitting devices in 1987, we have continued the research on the epitaxial growth of this system, estimation of its miscibility gap, proposal of novel substrates for the epitaxial growth and utilization of various crystallographic orientations to control its growth behaviors and properties. Also we found the true band-gap of InN of 0.7 eV which was much lower than the previously reported value. We are now concentrating on the development of high-performance laser diodes for optical communications systems by the pressurized-reactor metalorganic vapor phase epitaxial growth of InN, and the improvement of the efficiencies of optoelectronic devices by the nitrogen-polar epitaxial orientation of InGaAlN as well as new substrates with exotic materials such as ZnO and ScAlMgO4.

nitride semiconductors, epitaxial growth, electronic devices, light emitting devices
 Nitrogen-polar InGaNLEDs over the whole visible range.

Fig. 1 : Nitrogen-polar InGaNLEDs over the whole visible range. Nitride semiconductors have crystallographic polarity as shown in Fig. 2. Flipping this polarity can dramatically change the growth behaviors and device structures. N-polarity, which is opposite to the conventional Gapolarity, is effective for high In-content InGaN growth. LEDs over the whole visible range have been successfully fabricated.

Polarity of GaN

Fig. 2 : Polarity of GaN

ScAlMgO4 crystals proposed as a new substrate for the epitaxial growth of nitride semiconductors.

Fig. 3 : ScAlMgO4 crystals proposed as a new substrate for the epitaxial growth of nitride semiconductors. Sapphire commonly used as the substrate for nitrides has large lattice-mismatch to nitrides. Due to the misfit dislocations, devices with high performance cannot be expected. So we have proposed nearly lattice-matching substrate materials such as ZnO and ScAlMgO. Especially ScAlMgO4 has the habit of easy cleavage along its c-plane which is suitable for the preparation of atomically-flat surface, and the tolerance against the vapor phase epitaxial growth ambient.

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