SAGA UNIVERSITY
POWER ELECTRONICS LABORATORY (Prof. Kasu)

The world shortest wavelength- light from aluminum nitride (AlN)

 Aluminum nitride (AlN) is the direct-bandgap semiconductor with the highest energy gap (6.0 eV) among semiconductors. The value is much higher than that (3.5 eV) of GaN used in blue light emitting diode (LED).
For the purpose, we achieved p-type and n-type AlN semiconductors and fabricated its LED.

 The AlN LED emitted a light with a wavelength of 210 nm. The value is the shortest wavelength in the world.
The light will be used to decompose toxic chemical substances such as PCB and dioxin, kill bacteria,and fabricate nanometer-scale structures. (Nature2006, JACG Paper Award2010)

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Diamond RF Power Transistors

 The data transfer rate in communications is increasing very rapidly. Therefore, electronic devices that operate at higher frequencies and generate higher output power are urgently needed for the present and future communications systems. On the other hand, from the environmental and energy-saving viewpoints, higher power efficiency from semiconductor devices is required at the same time. Diamond is called the ultimate semiconductor because it intrinsically has many superior physical properties over conventional semiconductors. Diamond semiconductor will satisfy all of these requirements.

 Recently, the price of man-made diamond single-crystal is decreasing, in the near future, diamond wafer will be available at the reasonable price. For transistor, p-type and n-type diamond semiconductors are essential.
Recently we identified p-type conduction mechanism of hydrogen-terminated surface (APL2010) and achieved a hole sheet concentration (~1014 cm^-2) (APEX2009).
 We have achieved the highest power-gain cut-off frequency (fmax) (IEEE EDL2006) and RF output power (Pout) at 1 GHz (IEE Electron. Lett.2005), and opened diamond RF power amplifiers (PA) in microwave- and millimeter- wave range.

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Ion-implanted Diamond and its Power Transistors

 Ion implantation is the most widely used doping technology in semiconductor industries. But in diamond, the doping efficiency was quite low. But we proposed high-temperature, high-pressure (HPHT) post annealing, instead of conventional high-temperature annealing and increased doping efficiency by one order in magnitude. With this technology, we fabricated diamond transistor and demonstrated >1MV/cm and 500-oC operation (JJAP2010).
 With this technologies, we implanted various elements into diamond, and found arsenic (As) donors as n-type impurity. (JJAP2011).

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Nitride / Diamond Hetero-epitaxy and Nitride Transistor on Diamond

 We have achieved heterostructures of nitride and diamond with different crystal structures (JCG2009) and fabricated AlGaN/GaN high-electron mobility transistor (HEMT).
 We demonstrated the lowest thermal conductance (the lowest temperature rise during power operation) of AlGaN/GaN HEMT (ISCS2011, SemiForum Japan2011 Invited talks, 2010 Diamond Symposium Poster Award).

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