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Detailed Program
Paper Number : LD-I09
Time Frame : 13:55~14:20
Presentation Date : Friday, 28, November
Session Name : LED and Display Materials
Session Chair 1# : Joon Seop Kwak
Session Chair 2# : Yasushi Nanishi
Feasibility of Large Area Devices Based on Group III Nitrides
H. Fujioka
the University of Tokyo
It is generally believed that III-V semiconductor devices exhibit high performance but are very expensive because their fabrication process involves low throughput high temperature MOCVD or MBE growth on single crystal wafers. To fabricate large area III-nitride semiconductor devices such as solar cells or displays at a reasonable cost, development of a high throughput low temperature growth technique on low cost substrates is quite important. We have recently found that the use of growth technique called PSD (pulsed sputtering deposition) allows us to obtain device quality III nitrides even at room temperature [1]. PSD has attracted much attention of industry engineers because its productivity is much higher than that of MOCVD. In this technique, surface migration of the film precursors is enhanced and, therefore, the temperature for epitaxial growth is dramatically reduced. This reduction allows us to utilize various large area low cost substrates such as metals and mica that have not been used for growth of semiconductors so far due to their chemical vulnerability. In this presentation, we will discuss the feasibility of future large area flexible nitride devices prepared by PSD on these low cost substrates.
Typical GaN films prepared by PSD is highly resistive or lightly doped n-type but they can be doped into highly doped n-type or p-type by introduction of Si or Mg, respectively. With the use of this doping technique, we can fabricate various optical and electron devices. The most striking advantage in the device application of low temperature PSD process is suppression of phase separation reactions in InGaN, which is crucial for fabrication of long wavelength LEDs and solar cells. In fact, we have found that the use of PSD allows us fabricate a LED with a wavelength of 630 nm at a maximum process temperature of 480C. We have also fabricated AlGaN/GaN HEMT structure on Si substrates and confirmed its successful transistor operation. This successful operation opens up the possibility for the future low cost integration of GaN devices and Si CMOS devices on Si (110) substrates. We have also fabricated InN MISFETs with the use of PSD process and demonstrated large current and low leakage operation.
We then applied the present PSD technique for fabrication of LEDs on large area and flexible substrates such as metal foils and mica sheet. We have confirmed successful operation of full color RGB LEDs on these substrates. We have also worked on growth of GaN on amorphous SiO2 substrates. However, growth of crystalline GaN materials on top of amorphous materials is quite difficult. To solve this problem, we introduced graphene layers at the nitride/SiO2 interface and we succeeded in operation of RGB fill color InGaN LEDs on amorphous SiO2 substrates with the use of the graphene layers. This success implies that we could possibly fabricate InGaN full color displays on large area glass substrates with the use of the proposed process. These results clearly indicate that combination of the PSD low temperature growth technique and the large area substrate is quite promising for fabrication of future low cost large area nitride devices.
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