Impact of deep levels on the electrical conductivity and luminescence of gallium nitride codoped with carbon and silicon J. Appl. Phys. 98, 053704 (2005); 10.1063/1.2005379 A method to determine deep level profiles in highly compensated, wide band gap semiconductors J. Appl. Phys. 97, 083529 (2005); 10.1063/1.1862321 Neutron irradiation effect on radio-frequency magnetron-sputtered GaN thin films and Au/GaN Schottky diodes The electrical properties and deep level spectra in undoped n-GaN films irradiated by fast neutrons are reported. The electron removal rate was ϳ5 cm −1 , and the dominant deep states introduced by neutron damage were electron traps with activation energy of 0.75 eV. For high doses of 1.7ϫ 10 17 -10 18 cm −2 the material becomes semi-insulating n-type with the Fermi level pinned near E c − 0.85 eV. Deep level spectra are dominated by electron traps with activation energy of 0.75 eV, close to the energy of the Fermi level pinning in heavily irradiated material. Neutron irradiation also introduces a high density of centers giving rise to strong persistent photocapacitance. The observed phenomena are explained under the assumption that the dominant defects in neutron irradiated GaN are disordered regions produced by high-energy recoil atoms.

The effect of fast neutron ͑energy Ͼ0.1 MeV͒ irradiation on electrical properties and deep level spectra of undoped n-AlGaN films with Al mole fraction x = 0.4 are presented. In virgin samples, the properties are strongly influenced by deep traps at E c − 0.25 eV present in high concentrations ͑ϳ2.5ϫ 10 18 cm −3 ͒. Neutron irradiation with doses higher than 10 15 cm −2 leads to compensation of these centers with a removal rate of about 500 cm −1 . After neutron irradiation with high dose of 1.7ϫ 10 17 cm −2 the samples become resistive ͑Ͼ10 4 ⍀ cm͒, with the Fermi level pinned by new centers near E c − 0.35 eV introduced by irradiation with a rate of about 10 cm −1 . The neutron irradiation also gives rise to an increase of the concentration of deep hole traps with activation energy of 1 eV.

Undoped n-GaN grown by two different metallorganic chemical vapor deposition (MOCVD) techniques, standard MOCVD and epitaxial lateral overgrowth, and Mg-doped p-GaN prepared by hydride vapor phase epitaxy and molecular beam epitaxy were irradiated with fast reactor neutrons to the high fluence of 1018 cm−2. In such heavily irradiated samples the Fermi level is shown to be pinned in a narrow interval of Ec−(0.8−0.95) eV, irrespective of the starting sample properties. The Fermi level pinning position correlates with the measured Schottky barrier height in n-type GaN. The results are interpreted from the standpoint of the existence of the charge neutrality level in heavily disordered material. Based on published theoretical calculations and on deep level transient spectroscopy (measurements and lattice parameter measurements in irradiated material), it is proposed that the Fermi level could be pinned between the gallium-interstitial-related deep donors near Ec−0.8 eV and nitrogen-interstitial-related acceptors near Ec−0.9 eV

Deep traps in AlGaN/GaN heterostructures studied by deep level transient spectroscopy: Effect of carbon concentration in GaN buffer layersThe effect of neutron irradiation on the electrical properties of undoped n-AlGaN / GaN heterostructures is reported. The two-dimensional electron-gas ͑2DEG͒ mobility starts to decrease at neutron doses above 10 14 cm −2 , while the 2DEG concentration slightly increases at low doses and decreases dramatically for doses higher than 2.5ϫ 10 16 cm −2 . The result is that the mobility/ concentration product ͑a figure of merit for transistors͒ starts to decrease appreciably after the dose of 10 15 cm −2 . Capacitance-voltage and admittance spectroscopies, indicate that tunneling of electrons into the states near E c − 0.21 eV in AlGaN is a serious factor when cooling down the virgin or lightly irradiated samples. For heavily irradiated samples the states in AlGaN are close to 0.3 and 0.45 eV, respectively, from the bottom of the conduction band. Deep-level spectroscopy measurements reveal the presence of hole traps with apparent activation energies of 0.18 and 0.21 eV for lightly irradiated samples and deeper hole traps with activation energies of 0.6 and 1 eV in heavily irradiated samples.

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