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Abstract
Recently, there is an increasing demand for III-nitride semiconductor based optoelectronic devices, and especially for ultraviolet (UV) and Deep UV sources and sensors; however, the development and the performance of such devices is fundamentally limited by low carrier concentration, especially in p-type GaN and its alloys with aluminum, p-type AlxGa1-xN. Common acceptors such as magnesium (Mg), which function adequately in GaN, are often too deep in AlGaN alloys to allow significant acceptor ionization at room temperature. Various strategies such as short period superlattices are often incorporated into device architectures in order to enhance carrier levels in p-AlGaN. In this work, IR photocurrent spectroscopy in Mg-doped GaN, and Mg-doped AlxGa1-xN (0.15 < x < 0.52) was conducted by means of a YAG-pumped OPO/OPA tunable from 250 meV to 1.75 eV with the goal of observing and identifying energy levels associated with acceptor atoms of Mg in GaN and AlxGa1-xN. Infrared photocurrent spectra are presented from a variety of GaN and AlxGa1-xN test structures. Non-zero background response is associated with shallow extrinsic impurities and/or a continuum of shallow levels, photocurrent response peaks observed and associated with deep level donors. No evidence of acceptor ionization associated with Mg in magnesium-doped GaN and AlxGa1-xN is observed. A number of deep levels are observed in photocurrent spectra, including several 400 meV in GaN and low aluminum alloys, and one around 800 meV in higher aluminum alloys. Thermal analysis of Mg:GaN photocurrent data is consistent with the deep levels being electron donors. Finally, the effects of IR radiation on the UV optical output of forward biased commercial 365nm UV LEDs is investigated and reported.