Pt/Au/n-InGaN肖特基接触的电流输运机理

Current transport mechanism of Schottky contact of Pt/Au/n-InGaN

基于热电子发射和热电子场发射模式,利用I-V方法研究了Pt/Au/n-InGaN肖特基接触的势垒特性和电流输运机理,结果表明,在不同背景载流子浓度下, Pt/Au/n-InGaN肖特基势垒特性差异明显.研究发现,较低生长温度制备的InGaN中存在的高密度施主态氮空位(VN)缺陷导致背景载流子浓度增高,同时通过热电子发射模式拟合得到高背景载流子浓度的InGaN肖特基势垒高度和理想因子与热电子场发射模式下的结果差别很大,表明VN缺陷诱发了隧穿机理并降低了肖特基势垒高度,相应的隧穿电流显著增大了肖特基势垒总的输运电流,证实热电子发射和缺陷辅助的隧穿机理共同构成了肖特基势垒的电流输运机理.低背景载流子浓度的InGaN肖特基势垒在热电子发射和热电子场发射模式下拟合的结果接近一致,表明热电子发射是其主导的电流输运机理.

The Pt/Au Schottky contacts to InGaN samples with different background carrier concentrations are fabricated.The crystal qualities of InGaN samples are characterized by X-ray diffraction（XRD） and atomic force microscope（AFM）,and the correlation between threading dislocation density of InGaN and growth temperature is further clarified. The full width at half maximum（FWHM） values of the InGaN（0002） XRD rocking curves show that the density of threading dislocations in InGaN, which can seriously deteriorate InGaN crystal quality and surface morphology, decreases rapidly with increasing growth temperature. The Hall measurements show that the background carrier concentration of InGaN increases by two orders of magnitude as growth temperature decreases from 750 to 700℃, which is due to a reduced ammonia decomposition efficiency leading to the presence of high-density donor-type nitrogen vacancy（VN） defects at lower temperature. Therefore, combining the studies of XRD, AFM and Hall, it can be concluded that the higher growth temperature is favorable for realizing the InGaN film with low density of VN defects and threading dislocations for fabricating high-quality Schottky contacts, and then the barrier characteristics and current transport mechanism of Pt/Au/n-InGaN Schottky contact are investigated by current-voltage measurements and theory analysis based on the thermionic emission（TE） model and thermionic field emission（TFE） model. The results show that Schottky characteristics for InGaN with different carrier concentrations manifest obvious differences. It is noted that the high carrier concentration leads to the Schottky barrier height and the ideality factor obtained by TE model are quite different from that by TFE model due to the presence of high density of VN defects. This discrepancy suggests that the VN defects lead to the formation of the tunneling current and further reduced Schottky barrier height. Consequently, the presence of tunneling current results in the increasing of total transport current, which means that the defects-assisted tunneling transport and TE constitute the current transport mechanism in the Schottky. However, the fitted results obtained by TE and TFE models are almost identical for the InGaN with lower carrier concentration, indicating that TE is the dominant current transport mechanism. The above studies prove that the Pt/Au/n-InGaN Schottky contact fabricated using low background carrier concentration shows better Schottky characteristics. Thus, the properly designed growth parameters can effectively suppress defects-assisted tunneling transport, which is crucial to fabricating high-quality Schottky devices.