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

利用金属有机物化学气相沉积技术在蓝宝石衬底上制备了掺Fe高阻Ga N以及Al Ga N/Ga N高电子迁移率晶体管(HEMT)结构.对Cp_2Fe流量不同的高阻Ga N特性进行了研究.研究结果表明,Fe杂质在Ga N材料中引入的Fe~(3+/2+)深受主能级能够补偿背景载流子浓度从而实现高阻,Fe杂质在Ga N材料中引入更多起受主作用的刃位错,也在一定程度上补偿了背景载流子浓度.在一定范围内,Ga N材料方块电阻随Cp_2Fe流量增加而增加,Cp_2Fe流量为100 sccm(1 sccm 1mL min)时,方块电阻增加不再明显;另外增加Cp_2Fe流量也会导致材料质量下降,表面更加粗糙.因此,优选Cp_2Fe流量为75 sccm,相应方块电阻高达×10?/,外延了不同掺Fe层厚度的Al Ga N/Ga N HEMT结构,并制备成器件.HEMT器件均具有良好的夹断以及栅控特性,并且增加掺Fe层厚度使得HEMT器件的击穿电压提高了39.3%,同时对器件的转移特性影响较小.

Growths of Fe-dop ed GaN high-resistivity buffer layers for AlGaN/GaN high electron mobility transistor devices

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 Fe^3+/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, 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 /\Box, 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.