Mg Segregation, Difficulties of P-Doping in GaN
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layer consisted of 104 Å-thick layers of GaN, each followed by a 15 second exposure of Cp2Mg. During the Cp2Mg exposure, the TMGa was vented, but the NH3 and H2 remained flowing into the chamber. At the end of the growth samples were in`-`situ annealed at 850°`C for 10 min in order to dissociate Mg-H complexes and activate the Mg atoms. The p-i-n structures were also grown by MOCVD at the same temperature (1030°C) but with continuous Cp2Mg exposure and similar growth rate (5.5 Å/s) compared to (5.3Å/s) used for the delta doping. The same annealing at 850°C for 10 min was also performed. All crystals have been studied using transmission electron microscopy (TEM). Dopant concentration and impurity levels were determined using Secondary Ion Mass Spectrometry (SIMS) and Energy Dispersive x-ray spectroscopy (EDX). Crosssection samples were prepared along the [1 1 00] direction for Convergent Beam Electron Diffraction (CBED) in order to determine crystal polarity and along the [11 2 0] direction for high resolution cross-section studies (HREM). RESULTS Table I: Dopant and impurity concentration based on SIMS studies _________________________________________________________ Sample Mg ( cm-3 ) O ( cm-3) C (cm-3) Si (cm-3) _________________________________________________________ B 6e19 2.5e19 1.5e17 4e16 _________________________________________________________ 5e19 3e19 5e17 1e16 -1e17 M _________________________________________________________ Ba 4-6e19 7e19 1.5e18 1-2e19 ___________________________________________________________ P 3e19
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