Abstract
We investigate the impact of high-dose gamma-ray irradiation on the electrical performance of Ga-polar and N-polar GaN-based p–n diodes grown by metalorganic chemical vapor deposition. We compare the current density–voltage (J–V), capacitance–voltage (C–V), and circular transfer length method characteristics of the p–n diodes fabricated on Ga-polar and N-polar orientations before and after irradiation. The relative turn-on voltage increases for the Ga-polar diodes with an increasing irradiation dose, while it increases initially and then starts to decrease for the N-polar diodes. The p-contact total resistance increases for Ga-polar and decreases for N-polar samples, which we attribute to the formation of point defects and additional Mg activation after irradiation. The J–V characteristics of most of the tested diodes recovered over time, suggesting the changes in the J–V characteristics are temporary and potentially due to metastable occupancy of traps after irradiation. X-ray photoelectron spectroscopy and photoluminescence measurements reveal the existence of different types of initial defects and surface electronic states on Ga-polar and N-polar samples. Gallium vacancies (VGa) are dominant defects in Ga-polar samples, while nitrogen vacancies (VN) are dominant in N-polar samples. The presence of a higher concentration of surface states on Ga-polar surfaces than N-polar surfaces was confirmed by calculating the band bending and the corresponding screening effect due to opposite polarization bound charge and ionized acceptors at the surface. The difference in surface stoichiometry in these two orientations is responsible for the different behavior in electrical characteristics after gamma-ray interactions.
Highlights
INTRODUCTIONScitation.org/journal/adv attributed to the resulting opposite direction of spontaneous polarization
GaN is a promising semiconductor for use in RF and highpower electronics due to its wide bandgap, large breakdown field, excellent thermal conductivity, and high electron saturation velocity.1 Most current GaN-based electronic devices are configured as high electron mobility transistors (HEMTs), and high-power and high break-down-voltage Schottky or p–n junction diodes
We study the impact of gamma-ray irradiation on the electrical characteristics of Ga-polar and N-polar p–n diodes grown by metal–organic chemical vapor deposition (MOCVD) on sapphire substrates
Summary
Scitation.org/journal/adv attributed to the resulting opposite direction of spontaneous polarization.. Higher gamma-ray doses (∼210 kGy) were shown to degrade the device performance by increasing the Schottky barrier height, degrading the reverse J–V characteristics, or creating defect levels.. The sensitivities of the 2DEG mobility, charge, and barrier height to gamma-ray irradiation have been well studied in Ga-polar (0001) HEMTs and n-GaN Schottky diodes, there are no reports on the effect of gamma-ray radiation-induced damage on the performance of N-polar GaN p–n diodes. Studies comparing the impact of gamma-ray irradiation on Ga-polar and N-polar p–n diodes as the core elements of many devices are necessary to enable the design of new radiation-hard electronic devices. Ga-polar and N-polar diodes show different electrical characteristics after gammaray irradiation due to the creation of point defects and accumulation of charges trapped at surface states as a result of electron/hole generation during irradiation. J–V and CTLM measurements demonstrate the presence of both temporary and permanent damage to the diodes
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