Developing of Low-resistance Ohmic Contact on GaN HEMTs for High Operating Frequency Applications

Introduction: GaN high-electron-mobility transistors (HEMTs) technology currently offers exceptional device properties for next-generation high power and high frequency applications [1]. This is attributed to their high breakdown voltage and current capabilities. However, the formation of low source/drain contact resistance is required to lower the access resistance and thus enhance DC and RF performance [2].

Research Goal:

Material and Devices:

Analysis & Results:

     

Conclusion & Future Work: •  Development of low ohmic contact resistance with good surface morphology was realized on AlGaN/GaN on LR Si substrate. •  Recessed ohmic contacts with lower annealing temperatures could be adopted for better contact resistance Rc.

Abdulaziz BinKhudhayr 2176393, e-mail:2176393B@student.gla.ac.uk

University of Glasgow, charity number SC004401

Supervisor Name: Dr.Khaled Elgaid

Figure 2: Schematic diagram of AlGaN/GaN HEMT grown on Si.

Figure 4: Contact resistance for non-recessed & recessed metal stacks.

Figure 4: SEM images of (a) Ti/Al/Mo/Au and (b) Ti/Al/Ni/Au.

Figure 1:Energy Bandgap diagram.

Fabrication Process Material Growth

Two metal schemes with different interlayer metals were utilized for this project:

Table 2:Summary of the development process.

Table 1:Summary of the fabrication process.

Y_Sample A = 4.4354x + 8.4481 Y_Sample B= 4.0199x + 9.7737 Y_Sample C = 4.5482x + 22.694

0  

50  

100  

150  

200  

0   5   10   15   20   25   30   35  

R T, Ω

Gap spacing, µm

Sample A Sample B Sample C

Transfer length method (TLM) was used to characterize ohmic contacts.

Figure 3: Optical microscope image of TLM test structure 150 × 150 µm pads with the spacing 2.5, 5, 10, 15, 20, 25, 30, and 35 µm.

Scanned Electron Microscopy (SEM) of two metal stacks surfaces:

Since non-recessed Ti/Al/Mo/Au metal scheme resulted in the best ohmic contacts, Gate wrap-around d-mode d e v i c e s w e r e fabricated.

Figure 5: devices characteristic.

References: [1] Kolaklieva, L. and Kakanakov, R. (2009). Ohmic Contacts for High Power and High Temperature Microelectronics. Micro Electronic and Mechanical Systems [Accessed 5 Mar. 2015]. [2] U. K. Mishra, L. Shen, T. E. Kazior, and Y.-F. Wu. “GaN-based RF power devices and amplifiers,” Proc. IEEE, vol. 96, no. 2, pp. 287–305, Feb. 2008.