掺Fe高阻GaN缓冲层特性及其对AlGaN/GaN高电子迁移率晶体管器件的影响研究∗

摘要

Fe-doped high-resistivity GaN films and AlGaN/GaN high electron mobility transistor (HEMT) structures have been grown on sapphire substrates by metal organic chemical vapor deposition. The lattice quality, surfaces, sheet resistances and luminescent characteristics of Fe-doped high-resistivity GaN with different Cp2Fe flow rates are studied. It is found that high resistivity can be obtained by Fe impurity introduced Fe3+/2+ deep acceptor level in GaN, which compensates for the background carrier concentration. Meanwhile, Fe impurity can introduce more edge dislocations acting as acceptors, which also compensate for the background carrier concentration to some extent. In a certain range, the sheet resistance of GaN material increases with increasing Cp2Fe flow rate. When the Cp2Fe flow rate is 100 sccm (1 sccm=1 mL/min), the compensation efficiency decreases due to the self-compensation effect, which leads to the fact that the increase of the sheet resistance of GaN material is not obvious. In addition, the compensation for Fe atom at the vacancy of Ga atom can be explained as the result of suppressing yellow luminescence. Although the lattice quality is marginally affected while the Cp2Fe flow rate is 50 sccm, the increase of Cp2Fe flow rate will lead to a deterioration in quality due to the damage to the lattice, which is because more Ga atoms are substituted by Fe atoms. Meanwhile, Fe on the GaN surface reduces the surface mobilities of Ga atoms and promotes a transition from two-dimensional to three-dimensional (3D) GaN growth, which is confirmed by atomic force microscope measurements of RMS roughness with increasing Cp2Fe flow rate. The island generated by the 3D GaN growth will produce additional edge dislocations during the coalescence, resulting in the increase of the full width at half maximum of the X-ray diffraction rocking curve at the GaN (102) plane faster than that at the GaN (002) plane with increasing Cp2Fe flow rate. Therefore, the Cp2Fe flow rate of 75 sccm, which makes the sheet resistance of GaN as high as 1 × 1010 Ω/?, is used to grow AlGaN/GaN HEMT structures with various values of Fe-doped layer thickness, which are processed into devices. All the HEMT devices possess satisfactory turn-off and gate-controlled characteristics. Besides, the increase of Fe-doped layer thickness can improve the breakdown voltage of the HEMT device by 39.3%, without the degradation of the transfer characteristic.