Characterization of epitaxial GaAs MOS capacitors using atomic layer-deposited TiO2/Al2O3 gate stack: study of Ge auto-doping and p-type Zn doping
1 Institute of Materials Research and Engineering, A*STAR, (Agency for Science, Technology and Research), 3 Research Link, Singapore 117602, Singapore
2 School of Electrical and Electronic Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 639798, Singapore
3 Department of Electronic Science, University of Calcutta, 92-A. P. C. Road, Kolkata 700 009, India
4 Centre for Research in Nanoscience and Nanotechnology, (CRNN), University of Calcutta, JD-2 Sector III, Kolkata 700 098, India
5 Department of Electronics and ECE, Indian Institute of Technology, Kharagpur 721302, India
Nanoscale Research Letters 2012, 7:99 doi:10.1186/1556-276X-7-99Published: 2 February 2012
Electrical and physical properties of a metal-oxide-semiconductor [MOS] structure using atomic layer-deposited high-k dielectrics (TiO2/Al2O3) and epitaxial GaAs [epi-GaAs] grown on Ge(100) substrates have been investigated. The epi-GaAs, either undoped or Zn-doped, was grown using metal-organic chemical vapor deposition method at 620°C to 650°C. The diffusion of Ge atoms into epi-GaAs resulted in auto-doping, and therefore, an n-MOS behavior was observed for undoped and Zn-doped epi-GaAs with the doping concentration up to approximately 1017 cm-3. This is attributed to the diffusion of a significant amount of Ge atoms from the Ge substrate as confirmed by the simulation using SILVACO software and also from the secondary ion mass spectrometry analyses. The Zn-doped epi-GaAs with a doping concentration of approximately 1018 cm-3 converts the epi-GaAs layer into p-type since the Zn doping is relatively higher than the out-diffused Ge concentration. The capacitance-voltage characteristics show similar frequency dispersion and leakage current for n-type and p-type epi-GaAs layers with very low hysteresis voltage (approximately 10 mV).