Detection of Ga suboxides and their impact on III-V passivation and Fermi-level pinning
(Result of the month 06/2009)

(a) Ga 2p XPS spectrum of ~ 1.0 nm ALD Al₂O₃ deposited on a HF-last treated GaAs surface. The presence of Ga 3+ and Ga 1+ oxidation states are both detected. (b) C-V curves from devices with the same interface as the sample from (a). (c) C-V measurements performed at 150 °C (100 Hz curves were removed due to equipment-induced noise).

The passivation of interface states remains an important problem for III-V based semiconductor devices. The role of the most stable bound native oxides GaO_x (0.5 ≤ x ≤ 1.5) is of particular interest. Using monochromatic x-ray photoelectron spectroscopy in conjunction with controlled GaAs(100) and InGaAs(100) surfaces, a stable suboxide (Ga₂O) bond is detected at the interface but does not appear to be detrimental to device characteristics. In contrast, the removal of the Ga 3+ oxidation state (Ga₂O₃) is shown to result in the reduction of frequency dispersion in capacitors and greatly improved performance in III-V based devices.

(a) Ga 2p XPS spectrum of HF-last GaAs with ~1.2 nm ex situ deposited PECVD amorphous Si followed by ~1.0 nm ALD Al₂O₃ deposition. The Si deposition removes the Ga 3+ oxidation state while the Ga 1+ oxidation state remains. (b) C-V curves from devices with the same interface as the sample from (a). (c) C-V measurements performed at 150 °C. The frequency dispersion has been greatly reduced, demonstrating the correlation between the Ga 3+ oxidation state and interface traps that pin the Fermi level for these systems.

Multi-Module Cluster Tool
Combined SiGe-MBE, Metal MBE, Sputtering and Annealing for up to 4” Wafers

This system is capable of thin film deposition using PVD methods including electron beam evaporation, molecular beam deposition, sputter deposition and thermal evaporation methods. Additionally, in-situ characterisation techniques include angle-resolved monochromatic X-ray and ultraviolet photoelectron spectroscopy, scanning auger electron spectroscopy, atomic force and scanning tunnelling microscopy/spectroscopy. The system utilises 100 mm diameter wafers (for cleanroom process compatibility), and modified sample plates for the various deposition and characterisation techniques. Wafers are transported throughout the system in a UHV transfer system. Each deposition module has heating and rotational capability for the study of film uniformity and growth kinetics. Moreover, the system is expandable. The design permits the extension of the system to accommodate even more deposition or analytical techniques.

Only the in-situ capabilities of MBE growth modules and analysis modules acting in a combined approach as one big UHV system allowed the fully controlled deconvolution of the Ga 1+ state.

Authors:
¹ M. Milojevic, F. S. Aguirre-Tostado, R. M. Wallace
^1,2 C. L. Hinkle, E. M. Vogel
² A. M. Sonnet
³G. J. Hughes, B. Brennan

Institutes:
⁽¹⁾ Department of Materials Science and Engineering, The University of Texas at Dallas, Richardson, Texas 75080, USA
⁽²⁾ Department of Electrical Engineering, The University of Texas at Dallas, Richardson, Texas 75080, USA
⁽³⁾ School of Physical Sciences, Dublin City University, Glasnevin, Dublin 9, Ireland

Publications:
APPLIED PHYSICS LETTERS 94, 162101 (2009)

This result has been obtained with :
Multi-Module Cluster Tool
SPHERA
XM 1000

Detection of Ga suboxides and their impact on III-V passivation and Fermi-level pinning(Result of the month 06/2009)

Detection of Ga suboxides and their impact on III-V passivation and Fermi-level pinning
(Result of the month 06/2009)