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A systematic photoluminescence study of Be‐doped GaN grown by metal‐organic chemical vapor deposition is presented. All Be‐doped samples show the ultraviolet luminescence (UVLBe) band with a maximum at 3.38 eV and the yellow luminescence (YLBe) band with a maximum at ≈2.15 eV in GaN:Be having various concentrations of Be. The UVLBeband is attributed to the shallow state of the BeGaacceptor with a delocalized hole. The YLBeband is caused by a Be‐related defect, possibly the polaronic state of the BeGaacceptor with the charge transition level at 0.3 eV above the valence band. This broad band exhibits unusual properties. In particular, it always shows two steps in its thermal quenching. The second step at
T ≈ 200 K is attributed to the emission of holes from the 0.3 eV level to the conduction band. The origin of the first step remains unexplained. -
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We report on the growth and characterization of a new class of photocathode structures for use as electron sources to produce high brightness electron beams for accelerator applications. The sources are realized using III-nitride materials and are designed to leverage the strong polarization field, which is characteristic of this class of materials when grown in their wurtzite crystal structure, to produce a negative electron affinity condition without the use of Cs, possibly allowing these materials to be operated in radio frequency guns. A Quantum Efficiency (QE) of about [Formula: see text] and an emitted electrons’ Mean Transverse Energy (MTE) of about 100 meV are measured at a wavelength of 265 nm. In a vacuum level of [Formula: see text] Torr, the QE does not decrease after more than 24 h of continuous operation. The lowest MTE of about 50 meV is measured at 300 nm along with a QE of [Formula: see text]. Surface characterizations reveal a possible contribution to the MTE from surface morphology, calling for more detailed studies.
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GaN samples were implanted with Be and annealed in different conditions in order to activate the shallow BeGaacceptor. Low-temperature photoluminescence spectra were studied to find BeGa-related defects in the implanted samples. A yellow band with a maximum at about 2.2 eV (the YLBeband) was observed in nearly all samples protected with an AlN cap during the annealing and in samples annealed under ultrahigh N2pressure. A green band with a maximum at 2.35 eV (the GL2 band), attributed to the nitrogen vacancy, was the dominant defect-related luminescence band in GaN samples annealed without a protective AlN layer. The ultraviolet luminescence (UVLBe) band with a maximum at 3.38 eV attributed to the shallow BeGaacceptor with the ionization energy of 0.113 eV appeared in implanted samples only after annealing at high temperatures and ultrahigh N2pressure. This is the first observation of the UVLBeband in Be-implanted GaN, indicating successful activation of the BeGaacceptor.
