A Q-DLTS investigation of aluminum nitride surface termination
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A single crystal aluminum nitride (AlN) wafer surface was investigated via the use of a novel software-based, Charge-based Deep Level Transient Spectroscopy (Q-DLTS) apparatus, both before and after surface bond termination with hydrogen plasma. The sample was cleaned and metalized with a thermoresistive evaporator to create electrical contacts and then annealed in a helium atmosphere at 825 °C. Current-voltage (I-V) measurements were performed to investigate the nature of the metal/ substrate contacts. The effect of hydrogen termination was investigated and Arrhenius plots were produced from Q-DLTS spectra at temperatures ranging from 15.9 °C to 136.0 °C. Activation energies and capture cross-section values were calculated from the Q-DLTS spectra for traps existing in the AlN substrate surface. Prior to hydrogen termination, four charge traps were observed with activation energies of 0.31 eV, 0.61 eV, 0.56 eV, and 0.18 eV and capture cross sections 5.6 1021 cm2, 1.1 1016 cm2, 3.5 1019 cm2, and 1.3 1021 cm2, respectively After hydrogen termination, five charge traps were observed with activation energies of 0.31 eV, 0.61 eV, 0.52 eV, 0.19 eV, and 0.40 eV, and capture cross sections 4.9 1021 cm2, 1.3 1016 cm2, 2.9 1019 cm2, 3.1 1019 cm2, and 4.7 1019 cm2, respectively. Four of these peaks after termination are matched with the peaks prior to termination and the fifth peak appears to be the result of the hydrogen termination.
I. INTRODUCTION
Wide band gap semiconductors are of interest due to their ability to operate at high temperatures without suffering intrinsic conduction effects.1 These characteristics, as well as hardness and resistance to chemicals, make aluminum nitride (AlN) an attractive material for electronic packaging applications.2 Availability of single crystal AlN has been limited in the past, and its material characteristics have only recently been studied in detail.3–5 Polyakov et al.6 report characteristics on the deep centers of bulk AlN. Dominant electron traps are reported with ionization energies of 0.26 eV and 0.65 eV and concentrations of 1013/cm3 and 1015/cm3, respectively. Soltamov et al.7 identified two deep-level defects in AlN single crystals through electron paramagnetic resonance (EPR) and thermoluminescence (TL). These defects were attributed to oxygen located at the N site and carbon or silicon located at the Al site. Recently, developments in single crystal AlN production have allowed for further study of the material.8 In the present work, AlN surface traps were characterized through use of the Charge-based Deep Level Transient Spectroscopy (Q-DLTS) technique and the effects of exposure to hydrogen plasma were studied. Arrhenius a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.50 1198
J. Mater. Res., Vol. 27, No. 8, Apr 28, 2012
http://journals.cambridge.org
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data was generated from Q-DLTS spectra taken at a series of temperatures which provided the activation energies and cap
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