Optimization of GaN Growth Conditions for Improved Device Performance

By accurately optimizing the growth conditions for an oxygen doped AlN nucleation layer and for the subsequent epitaxial process the crystal quality of our GaN could drastically be improved. In X-ray diffraction (XRD) analyses we observed FWHM values of 39 arcsec and 114 arcsec for the symmetric (004) and asymmetric (114) reflection, respectively. Consequently, the nominally undoped samples showed semi-insulating behavior in Hallmeasurements. By in-situ deposition of a SiN interlayer, the dislocation density could be reduced by more than a factor of 2, reaching a value of 4 · 10 cm . Samples with this low dislocation density showed an extremely narrow X-ray FWHM of 71 arcsec for the asymmetric (114) reflection along with a narrow linewidth of 870μeV in photoluminescence (PL) for the donor bound exciton (DX) at a temperature of 10K. Atomic force microscopy (AFM) yielded a very low rms-roughness of about 0.14 nm across a 4μm scan area. Finally, the excellent crystal quality could be confirmed by growing AlGaN/AlN/GaN heterostructures with a low sheet resistance of 330Ω/2.