非故意掺杂与半绝缘GaN缓冲层上的AlGaN/GaN异质结构的高温电子输运特性

研究了非故意掺杂(UID)与半绝缘(SI)GaN缓冲层(BL)上的Al0.35Ga0.65N/GaN异质结构高温下的电子输运特性,应用Hall效应系统地测量了样品在高温下的电子面密度和电子迁移率随温度变化的关系.实验发现,高温下AlGaN/GaN异质结构的电子迁移率主要受到LO声子散射的作用,其中,UID-BL样品的电子面密度随温度升高而逐渐上升,SI-BL样品的电子面密度则随温度升高呈现先下降再平衡后上升的规律.对相应的未生长AlGaN势垒层的本征GaN薄膜的高温电阻特性分析表明,随着温度的升高,UID-BL样品的电子迁移率受到背景载流子的影响逐渐增大;SI-BL样品的电子迁移率在室温附近受附加位错散射的影响较大,600K以后受背景载流子的影响缓慢增强,这对于研究AlGaN/GaN异质结构器件的高温特性具有很好的参考意义.另外,由理论计算可知,高温下二维电子气(2DEG)逐渐向势垒层和缓冲层内部扩展,电子在第一子带的占据从室温下的86%下降到700K时的81%.

High temperature electron transport properties of AlGaN/GaN heterostructures based on unintentionally doped and semi-insulating GaN buffer layer

High temperature electron transport properties of Al0.35Ga0.65N/GaN heterostructures grown on unintentionally doped (UID) and semi-insulating (SI) GaN buffer layer (BL) have been investigated. Electron sheet density and electron mobility dependence on temperature have been systematically measured by Hall effect measurement. It is found that the electron mobility of AlGaN/GaN heterostructure is mainly limited by the longitudinal optical (LO) phonon scattering at high temperature. The sheet carrier density of AlGaN/GaN heterostructure based on UID-BL increases gradually with the increase of temperature, while it decreases firstly, and then increases for the sample based on SI-BL. It is indicated by the analysis of the high temperature resistance properties for the corresponding UID-GaN and SI-GaN films, that the effect of the background carrier-limited electron mobility increases gradually for the UID-BL sample, while for the SI-BL sample the electron mobility is mainly limited by the additional dislocation scattering around room temperature but the background carrier limited effect increases after 600 K. This is meaningful for investigating the high temperature property of the devices based on AlGaN/GaN heterostructure. Moreover, the theoretical calculation indicates that, the two dimensional gas (2DEG) has expanded to the AlGaN barrier layer and the deeper position of the GaN buffer layer, and the electron occupation in the first subband decreases to 81% at 700 K.