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Advenced Power Electronics Research Center

GaN Power Device Team

Research Activity
(1) Material science of GaN growth
(2) Development of AlGaN/GaN HEMT power switching devices
(3) Feasibility study of AlGaN/GaN HEMTs in switching regulators


Members
 Dr. M. Shimizu, E-mail: mitsu.shimizu(at)aist.go.jp
 Dr. X. Q. Shen, E-mail: xq-shen(at)aist.go.jp 
 Dr. T. Ide, E-mail: t-ide(at)aist.go.jp
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(1)GaN growth on Si substrate using MOCVD

 In actual applications in power electronics based on low-cost markets, the reduction of the device cost is important. The substrates using GaN single crystals or the SiC crystals have been developed, however they are very expensive. Thus the development of GaN growth on Si substrate with low-cost is important. Recently the growth technique of the GaN on Si substrate using the AlN/GaN super-lattice structure is developed by Prof. T. Egawa in NIT.
 In our group, MOCVD growth is employed for developing device structures, and the material science of the GaN growth on Si substrate has been investigated.




Stress of GaN layer on Si substrate can be controlled using AlN/AlGaN super-lattice structure







AFM measurement of GaN layer on Si substrate
 Some defects can be found, but surface is flat.
 Steps of lattice can be found.



GaN on Si substrate using AlN/GaN super-lattice
(2 mm X 2 mm, RMS = ~ 0.3 nm)



(2)Normally off operation

The AlGaN/GaN HEMTs operate generally in normally-on mode. On the other hands, in power switching application the normally-off mode operation is desired.  In our group, we proposed two types of structure giving normally-off mode operation.

  (1) p-InGaN cap layer under the gate electrode.
  (2) HEMT using channel of AlGaN/GaN/AlGaN double hetero-structure.


   (A)p-InGaN cap layer under the gate electrode
     
  





Drain voltage - drain current characteristics
  
(1)Threshold voltage : ~ 0.5 V
(2)Maximum drain current : > 200 mA / mm
(3)Maximum Gm : 120 mS/mm
(4)On-resistance Vg =3 V : 20 W/mm





   (B) HEMT with AlGaN/GaN/AlGaN double heterostructure
 




Drain voltage vs. current characteristics of DH HEMT
  


(3)Development of Equivalent Circuit for AlGaN/GaN HEMT


 Feasibility of AlGaN/GaN power device in switching regulators.


  
  
 (1) current collapse is included.
  (2) leakage current in GaN layer under hetero-junction channel.
  (3) 2-DEG model is included.


  
  
  


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