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Characterization of epitaxial GaAs MOS capacitors using atomic layer-deposited TiO2/Al2O3 gate stack: study of Ge auto-doping and p-type Zn doping

Goutam Kumar Dalapati1*, Terence Kin Shun Wong2, Yang Li2, Ching Kean Chia1, Anindita Das34, Chandreswar Mahata5, Han Gao1, Sanatan Chattopadhyay34, Manippady Krishna Kumar1, Hwee Leng Seng1, Chinmay Kumar Maiti5 and Dong Zhi Chi1

Author Affiliations

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

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Nanoscale Research Letters 2012, 7:99  doi:10.1186/1556-276X-7-99

Published: 2 February 2012

Abstract

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).

PACS: 81.15.Gh.

Keywords:
epitaxial-GaAs; Ge out-diffusion and auto-doping; ALD; high-k dielectrics.