Photoluminescence, Capacitance-Voltage, and Variable Field Hall Effect Measurements of Mg-Doped InN
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0955-I08-06
Photoluminescence, Capacitance-Voltage, and Variable Field Hall Effect Measurements of Mg-Doped InN Craig H. Swartz1, Steven M. Durbin1, Roger J. Reeves1, Katherine Prince2, John V. Kennedy1,3, Sandeep Chandril4, Thomas H. Myers4, and Damian Carder1 1 The MacDiarmid Institute for Advanced Materials and Nanotechnology, Christchurch, 8140, New Zealand 2 Australian Nuclear Science and Technology Organization, Lucas Heights, Australia 3 GNS Science, Lower Hutt, 5040, New Zealand 4 Physics, West Virginia University, Morgantown, WV, 26506
INTRODUCTION All as-grown unintentionally doped InN is n-type, which presently hampers efforts to realize p-n junction devices from this material. The tendency of native defects in InN to form donors manifests itself particularly severely at surfaces where high levels of electron accumulation are observed.1,2 This creates difficulties when assessing the impact of dopants, as electrical measurements are often dominated by the surface charge layer. Recently, Jones et al. reported capacitance-voltage (CV )data which provided the first indirect evidence for buried ptype layers in Mg-doped InN thin films.3 Quenching of photoluminescence (PL) emission in heavily Mg-doped layers was reported. Also, Cimalla et al. recently used sputter depth profiling and ultraviolet photoelectron spectroscopy to show a discontinuity in the conductivity of Mgdoped InN in the near surface region, consistent with a depletion region between n- and p-type layers.4 In the present study we use a combination of variable magnetic field Hall effect, PL and CV analysis to study the electrical and optical properties of a wide range of Mg concentrations in plasma-assisted molecular beam epitaxy (PAMBE) grown InN epilayers, some of which exhibit distinct p-type conduction. We have also observed evidence of a p-type conducting layer in layers grown on (111) yttrium-stabilised zirconia (YSZ) substrates – originally employed due to their small (2.5%) mismatch to InN – with no Mg.5 EXPERIMENT All films were grown at the University of Canterbury in a Perkin-Elmer 430 PAMBE system. Active nitrogen was provided by an Oxford Applied Research HD-25 RF plasma source operated at 150 W and 1.3 sccm, and In by an effusion cell operated at a flux of 1.2×1015 atoms cm-2s-1 as measured by a quartz crystal microbalance. Substrates include (111) YSZ, sapphire with a 150 nm buffer layer of PAMBE GaN, and 1.6 µm thick metal-organic chemical vapor deposition (MOCVD) GaN templates with a 150 nm PAMBE-grown GaN buffer layer. For samples grown on GaN, 30 nm of undoped InN was followed by 500 nm of the Mg-doped InN layer. Mg cell temperatures were chosen based on theoretical flux curves calibrated against crystal microbalance measurements at elevated temperature; particle-induced x-ray emission (PIXE) performed on the most heavily-doped sample measured total Mg content within a factor
of 3 of the predicted value. The Mg cell was held at room temperature for all growth experiments using YSZ substrates. The growth temperature for all I
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