Analysis of simultaneous occurrence of shallow surface Fermi level pinning and deep depletion in MOS diode with Mg-ion-implanted GaN before activation annealing

Abstract

The characteristics of a MOS diode with Mg-ion-implanted GaN before activation annealing were investigated. Mg ion implantation onto n-GaN with slightly high Si doping concentration (5×10 17 cm -3 ) was performed with a moderate dosage (1.5×10 12 cm -2 ). The completed MOS diode showed n-type features. The capacitance-voltage (C-V) and capacitance-frequency (C-f) characteristics of the MOS diode indicated that shallow surface Fermi level pinning and deep depletion occurred simultaneously. By applying the conductance method to the measured C-f characteristics, a discrete level at 0.2-0.3 eV below the conduction band edge was detected. On the basis of the simulation of the high-frequency-limit C-V curve, the detected discrete level distributed in the bulk of n-GaN rather than at the insulator/semiconductor interface, so that it caused surface Fermi level pinning at a relatively shallow energy level and deep depletion owing to its acceptorlike nature simultaneously.

Encapsulant-Dependent Effects of Long-Term Low-Temperature Annealing on Interstitial Defects in Mg-Ion-Implanted GaN

“…On the basis of a DLTS study, several defect levels at 0.2 -1.0 eV from the conduction band edge EC were detected and found to vary depending on the annealing temperature up to 1000 ℃ [23]. Moreover, the C-V method for the MOS diodes revealed an acceptor-like defect level located at 0.7 -0.8 eV from EC for Mg implantation at 50 keV and a dose of 1.5×10 11 cm -2 and that located at 0.2 -0.3 eV from EC at a higher Mg dose of 1.5×10 12 cm -2 [24][25][26][27]. The origin of the former level is likely to be interstitial N (Ni) [26], whereas that of the latter level was found to be the divacancies of Ga and N (VGaVN), as determined by the combination of the C-V method and positron annihilation spectroscopy (PAS) [28].…”

“…The control of defects in Mg-ion-implanted GaN may be possible by annealing at a temperature much lower than that necessary for Mg activation. The effects of lowtemperature annealing on defects in Mg-ion-implanted GaN have been studied in detail by deep-level transient spectroscopy (DLTS) using Schottky barrier diodes [23] and capacitance-voltage (C-V) methods using MOS diodes [24][25][26][27][28]. On the basis of a DLTS study, several defect levels at 0.2 -1.0 eV from the conduction band edge EC were detected and found to vary depending on the annealing temperature up to 1000 ℃ [23].…”

Investigation of gap states near conduction band edge in vicinity of interface between Mg-ion-implanted GaN and Al2O3 deposited after ultra-high-pressure annealing

“…As mentioned above, the discrete level at around E C -0.25 eV was detected in the as-implanted sample. [27][28][29] This level was assigned to the V Ga V N defects generated by Mg implantation by a combination of electric measurement and PAS. 29) Upon annealing at 1250 °C, however, this discrete level disappeared and part of the U-shaped distribution was detected in the range from E C -0.15 eV to E C -0.45 eV.…”

“…According to the electrical measurements of Mg-implanted GaN before annealing, a defect level at 0.25 eV below the conduction band edge (E C ) has been detected. [27][28][29] This defect level does not disappear after annealing at 500 °C. 27) The combination of electrical measurement and PAS revealed that this discrete defect level at E C -0.25 eV was assigned to V Ga V N .…”