AVS 59th Annual International Symposium and Exhibition
    Electronic Materials and Processing Tuesday Sessions
       Session EM-TuM

Paper EM-TuM9
Metastable Centers and Localized States in AlGaN/AlN/GaN Heterostructures Studied by C-V, Admittance Spectroscopy, and DLTS

Tuesday, October 30, 2012, 10:40 am, Room 009

Session: Electrical Testing and Defects in III-V’s
Presenter: A.Y. Polyakov, Institute of Rare Metals, Russian Federation
Authors: A.Y. Polyakov, Institute of Rare Metals, Russian Federation
N.B. Smirnov, Institute of Rare Metals, Russian Federation
A.V. Govorkov, Institute of Rare Metals, Russian Federation
E.A. Kozhukhova, Institute of Rare Metals, Russian Federation
S.J. Pearton, University of Florida
F. Ren, University of Florida
L. Lu, University of Florida
S.Y. Karpov, Soft-Impact, Ltd, Russian Federation
W. Lim, Samsung LED, Republic of Korea
Correspondent: Click to Email
A set of AlGaN/AlN/GaN high electron mobility transistor (HEMT) structures with Al composition in the AlGaN barrier changing from 20% Al to 50% Al was grown by metalorganic chemical vapor deposition (MOCVD) on sapphire and studied by means of capacitance-voltage C-V measurements, admittance spectroscopy, reverse deep levels transient spectroscopy. C-V and admittance measurements were performed in the dark and after illumination. The results suggest the presence in the AlGaN barriers of deep negatively charged traps of high concentration measurably shifting C-V characteristics to more positive voltages. The density of negatively charged centers can be increased by cooling at high reverse bias. These centers are believed to have a relatively high barrier for capture of electrons. Their thermal activation energy is estimated as 0.6-0.85 eV, the optical ionization energy is close to 1.7 eV. The presence of such centers explains lower than expected from modeling threshold voltages of the studied structures. Admittance spectroscopy also reveals consistent presence of features corresponding to apparent activation energy 0.11-0.13 eV for measurements at reverse voltages corresponding to a peak in AC conductance dependence on bias. These peaks in conductance and steps in admittance were attributed to transitions from the ground state in the triangular well near the AlN/GaN interface to the quasi continuum of excited states in the well with subsequent thermal emission into the conduction band. For samples illuminated at low temperature admittance spectra show unusual peaks in conductance with the activation energy close to the activation energy of thermal emission from the traps responsible for persistent photoconductivity.